International society of sports nutrition position stand: nutrition and weight cut strategies for mixed martial arts and other combat sports

In summary, combat sports involve high-intensity actions that are metabolically demanding, so athletes must have good metabolic flexibility and efficiency. Research on martial arts has generally found that the energy demands of an average karate fight lasting 4 min and 27 s come from aerobic (77.8%), anaerobic alactic (16.0%), and lactic (6.2%) energy pathways [25]. Moreover, the existing research is consistent; independent of the combat sport discipline, as the duration of the match increases, the contribution of the aerobic system increases, yet anaerobic alactic pathways remain vital for executing high output bursts of skill applications. It is important to note that sports nutrition professionals should be aware of the numerous factors that can influence energetic demands, energy expenditure, and ultimately metabolic cost. With an understanding of the complex interaction of energy systems, sports nutrition professionals can effectively manage the total daily energy expenditure requirements based on the combat athletes training volumes, intensities, and body composition, and adjust the calories and macronutrients, as necessary.

Combat athletes may benefit from maintaining adequate levels of aerobic fitness along with managing their body mass and body composition during the general preparation phase; especially as it pertains to health and performance. In this respect, an athlete’s “walk-around weight” is an important metric outside of fight camp. Walk-around weight is generally defined as the athlete’s weight outside of the fight camp measured against their weight class. It is estimated that combat athletes lose an average of 5% body mass during rapid weight loss [37]. Garthe et al. [38] reported minimal losses in performance measures (1-repetition-maximum (1RM) tests, 40-m sprint, and countermovement jump) in individuals engaged in weight loss at rates of 0.7% per week. Based on typical loss during RWL and weekly body mass loss of 0.5–1% over an 8-week camp, the authors suggest that the ideal maximum walk-around weight should range from 12% to 15% above the athlete’s desired weight class. The authors speculate this will minimize decreases in performance while allowing the athlete to make the weight of their desired class. In context, this would have a UFC male middleweight, required to make 185Ibs for their weight division, sustaining a weight of 207Ibs–212Ibs in the off camp phase. However, these numbers have not yet been fully substantiated through research and while there is scant research on this notion, practical application suggests this range should be effective for a longitudinal weight descent that simultaneously supports conditioning, skill training, and recovery. During fight camp, the athlete will utilize dietary and exercise strategies that create a caloric deficit to decrease body mass and must ensure this deficit does not negatively impact training performance, overall health, and any potentially harmful long-term metabolic adaptations. Although 12–15% may be potentially optimal, larger reductions in body mass are common practice in combat sports [39].

Moreover, research has shown large decreases in testosterone below clinical reference ranges (<5 mmol·L⁻¹), as well as a decrease in resting metabolic rate, when losing 13–15% body mass over an 8-week camp [40]. Accordingly, the ranges of 12–15% body mass above the weight class may be the upper limits of a suitable longitudinal weight descent.

Combat athletes exceeding 12–15% body mass will require more significant energy restriction, and if completed over a shorter duration than 8 weeks, the caloric deficit needed to achieve the desired changes in body mass may put athletes at a greater risk for low energy availability. While much of the available literature on low energy availability has indicated systemic reductions in various hormones, the impact of these energy deficits may also result in negative changes related to skill acquisition, concentration, motivation, and recovery [41]. This is a critical area for future research, which aims to identify suitable losses in body mass that will allow for sustained longitudinal health and performance for combat athletes.

Like many other types of athletes, the success of combat athletes is highly dependent on their ability to consume adequate energy to meet the demands of multiple daily training sessions. Daily energy needs are based on the athlete’s body mass, body composition, training volumes, goal weight, and total daily energy expenditure (TDEE). The caloric needs of elite combat athletes engaged in moderate to high-intensity training differ significantly from those of the general population. To maintain weight, athletes must balance caloric intake with total energy expenditure, so determining TDEE with reasonable accuracy is necessary. Metabolic carts and indirect calorimetry are the most accurate methods to determine a combat athlete’s resting metabolic rate (RMR). In the absence of these modalities, total energy expenditure can be calculated using the Mifflin – St Jeor equation, which considers age (years), sex, height (cm), weight (kg), and an estimate of the athlete’s physical activity level (PAL) [42,43]. The Cunningham equation can also be used which determines BMR via, BMR (kcal/day) = 500 + 22 × (lean body mass). The Cunningham equation determines the energy required at rest by considering lean body mass instead of overall body weight and then factoring in the combat athlete’s physical activity level. Another simple estimate of total energy expenditure is to multiply the athlete’s weight (lbs.) by 14 and add the estimated calories burned by training and the thermic effect of food [43], which is typically 3% to 10% of calorie expenditure [44]. These methods provide a reasonable estimate for caloric expenditure which should then be adjusted to best match the combat athletes’ current body mass, training demands, and for the maintenance of a desired weight and body composition.

Combat athletes meet their caloric requirements by consuming adequate amounts of carbohydrates, protein, and fat. Carbohydrate requirements vary significantly based on body mass, the type of workout, training intensity, and the training phase in which they are engaged [43]. Generally, combat athletes should anticipate consuming between 3 to 5 g of carbohydrates per kg of body mass daily for light activity and between 8 to 12 g of carbohydrates per kg of body mass daily for intense training [43]. Although research suggests 8–12 g of carbohydrate per kg of body mass may be required for endurance athletes, this amount is likely to be excessive for combat athletes competing in a weight-specific sport. However, one should not overestimate the merit of consuming these amounts for post weigh-in refueling. Fruits, vegetables, whole grains, sweet potatoes, rice, pasta, and legumes are recommended sources of carbohydrates during the “off camp” phase, instead of processed sugars [43].

Fat requirements for the combat athlete are the same as nonathletes and should be 20–35% of total daily calories or approximately 1.0 g of fat for every kilogram of body mass per day. While being the most energy-dense nutrient, dietary fat is a common target for people who need to restrict energy intake; however, consuming daily fat intake below 15–20% of total calorie intake is not advised [45]. However, fats are often restricted during longitudinal weight descents to meet the restriction in calories while preserving carbohydrate and protein intakes. Optimal fat sources include salmon, lean meats, eggs, nuts and nut butters, avocado, coconut, and olive oil [43], and not saturated or trans fats from fried foods, processed cheeses, or hydrogenated oil.

Protein requirements range from a minimum of 1.2 g per kg of body mass per day and up to 2.4 g of protein per kg of body mass or 15% to 30% of total calories [43] which is a higher intake relative to the average sedentary individual [46,47]. In addition to promoting muscle recovery and enhancing muscle protein synthesis, increased protein intake results in favorable changes in body composition, especially when in an energy deficit. It is imperative to meet protein requirements since, unlike fats and carbohydrates, there is a limited storage pool of proteins and their constituent amino acids. If combat athletes are not meeting protein requirements via sufficient food intake, protein supplementation in the form of protein powders or ready to drink beverages might be needed to achieve adequate energy and protein needs. The sports nutrition professional can assist combat athletes in building proper meals that meet energy and macronutrient demands, with strategically timed windows around their training sessions.

Although micronutrients are considered essential for optimum health, their ability to function as ergogenic aids is unlikely [43], mainly when overt deficiency was present before vitamin and mineral supplementation. Nonetheless, studies have highlighted that consuming a multivitamin can help athletes meet their daily micronutrient needs, which are higher compared to the general population [48].

Another emerging area of research is “periodized nutrition,” which refers to the strategic use of specific nutritional interventions to support exercise performance [49]. This is not a new concept. It is well established that protein should be consumed post-exercise, as this can optimize net protein synthesis. However, most nutritional recommendations for athletes aim to promote acute recovery after exercise and are not specific regarding the type of training or intensity [49]. Pairing specific nutritional goals commensurate with the phases of training may be beneficial for the combat athlete whose nutritional needs extend beyond recovery [49]. For example, protein needs should be based on increasing or maintaining a suitable body composition in the general preparation phase. Moreover, protein needs should be tailored to recovery and minimizing loss of lean body mass during fight camp. The authors recommend creating individualized nutrition and training programs, ideally before the start of fight camp, and adjusting as needed.

Prior to entering fight camp, it is important to conduct a thorough assessment of the specific demands of the combat sport discipline and the individual athlete’s needs. An assessment enables the training team to determine which nutritional strategies should be implemented for the combat athlete and what needs to be achieved before fight camp. Information such as the athlete’s anthropometrics, previous weight cut practices, the number and duration of weight cuts, and current dietary intake (including supplementation) should be assessed. Daily food logs or dietary tracking apps are accessible to most individuals and are ideal for assessing and monitoring dietary intake. The combat athletes’ previous practices can be measured against an evidence-based approach and revised when warranted.

While there are numerous measures that may have utility in optimizing performance through nutritional interventions. The sports nutrition professional may be most concerned with data including resting metabolic rate (RMR), body composition including fat-free mass (FFM), body fat percentage, and total body water (TBW). First, this data may assist in developing nutrition strategies that will meet the energy demands for combat athletes through all phases of training. Additionally, via determining total body mass and fat-free mass, predictive equations can be used to establish the feasibility of the combat athlete competing in their weight division. While there are no specific validated equations for predicting the efficiency and safety of longitudinal weight descents, the UFC Performance Institute has developed the Weight Making Preparedness Score (WMPS). The equation requires data on Fat-Free Mass, the athlete’s Total Mass over the target weight, Fat Mass, and Resting Metabolic Rate. The equation can be found on pp. 242 of the Cross-Sectional Performance Analysis of the UFC Athlete, vol. 2.

This data may also have utility for determining the required rate of a longitudinal weight descent in fight camp; and for monitoring any potential deviances in resting metabolic rate. Accordingly, the sports nutrition professional may track these measures (body composition and resting metabolic rate) and adjust nutritional strategies as needed to ensure adequate energy intake and an efficient longitudinal weight descent.

There are various methods available for testing body composition, which can be used by researchers and trainers. Common methodologies for measuring body composition include hydro-densitometry, air displacement plethysmography, multifrequency bioelectrical impedance analysis (MF-BIA), ultrasound, 3D scanning, skinfold thickness, and dual-energy X-ray absorptiometry (DXA) [50] Each method has its own strengths and weaknesses, as assessed by researchers. Dual-Energy X-ray Absorptiometry (DXA) is considered one of the most accurate methods for assessing body composition. DXA provides information on total and regional fat mass, fat-free mass, percent fat, and bone mineral density [51]. Additionally, DXA can provide limb-specific estimations of fat mass and fat-free mass, which is useful for measuring and tracking injury/recovery and fat loss for weight cutting [52,53]. Essential DXA measurements for combat athletes include body composition analysis, muscle-fat analysis, and obesity analysis. It should be noted that DXA, as with all modalities, is subject to confounding results from inter-assessment differences in hydration, glycogen and muscle creatine levels, all which can vary significantly in combat athletes [54].

Bioelectrical impedance analysis (BIA) is an inexpensive and reliable assessment tool used for body composition. Unlike DXA, BIA estimates total body water, which can be useful for estimating the impact of fluid loss on pre- and post-training and pre- and post-weight-in. Important BIA measurements to consider in combat athletes are body composition analysis, muscle-fat analysis, and obesity analysis. Compared to DXA, BIA has been shown to underestimate fat mass and overestimate fat-free mass [51,55–60]. Despite this variability in findings with BIA, it can still be considered a useful tool for measuring body composition change, which is especially important for sports nutrition professionals assessing directional change [51,55,61].

As part of a comprehensive assessment, when possible, blood analysis screenings may provide insight into a combat athlete’s health and performance. Blood work is often used as a screening tool to identify potential deficiencies in vitamins, minerals and microminerals such as iron, as well as evaluating oxidative stress and inflammation. Additionally, blood work can provide the status of red blood cell populations as well as markers such as cortisol and creatine kinase, which can provide insights into overtraining, readiness to train, and other measures such as protein turnover [62]. Biomarkers such as vitamin D and iron are well established and commonly assessed, whereas others need further research (e.g. fatty acids) to demonstrate their utility in sport [62]. Newer methods that estimate plasma volume using groups of biochemical markers are also showing promise. Such markers may provide additional support for monitoring a combat athlete’s adaptation to training.

Supplementation with various dietary ingredients is a widespread practice for many athletes to heighten performance and augment training adaptations. While research on combat sport athletes is limited, some evidence is available which suggests certain ingredients may enhance their performance. The phase of training or preparation whereby an athlete may choose to utilize a certain dietary supplement is an important consideration. For many supplements, utilizing them during a general preparation phase is a prudent consideration. This allows for experimenting with a given supplement and the dosing to optimize the effects on the combat athlete. Some supplements, however, rely on their accumulation in skeletal muscle (e.g. creatine, beta-alanine, etc.) to exert their ergogenic effects. In these situations, the off-camp/general preparation phase allows for a sufficient window of time for these supplements to reach ergogenic levels. Notwithstanding these considerations, the following supplements may be considered for their ability to augment performance and recovery potential of combat athletes: Caffeine [63], beta-alanine [64], sodium bicarbonate [65], creatine [66], and nitrates [67,68]. In addition, supplements such as essential amino acids [69], leucine [70], [71], branched-chain amino acids [72–74], and β-Hydroxy β-methylbutyrate [75], may promote increases in protein synthesis or decrease delayed onset muscle soreness.

Caffeine is a long-standing supplement in the realm of athletic performance. Caffeine use has been shown to improve physical and cognitive performance in several sports due in large part to its ability to modulate central and peripheral nervous system activity [63]. Several studies support the use of caffeine among combat athletes [76–78]. A systematic review conducted by Lopez-Gonzalez et al. [79] found that supplementation with 3–6 mg/kg of caffeine increased the glycolytic contribution (as evidenced by increased blood lactate concentrations) to energy metabolism during the execution of real or simulated combat bouts. Caffeine supplementation also improved levels of strength, power, and upper arm muscular endurance, and these effects were not associated with an increase in the perceived exertion by the athlete [80].

A systematic review by Lopes-Silva & Franchini in 2021 [81] examined the isolated and combined effects of sodium bicarbonate (NaHCO₃) and β-alanine (BA) supplementation on the performance of combat sports athletes. The results showed that acute and chronic isolated ingestion of NaHCO₃ and chronic BA are effective in improving performance in the Wingate test, Upper Wingate test, Special Judo fitness test and Karate-specific aerobic test, which translates to advancing combat sports athlete’s performance via muscle functionality and localized muscle buffering capacity. Additionally, the co-ingestion of BA and NaHCO₃ resulted in additional improvements across testing. However, the authors found no benefit to taking these supplements individually.

Halz et al. [82] conducted a study with 16 elite judo athletes (21.8 ± 2.5 years old) where athletes were randomly assigned to receive either BA (4 g/d over the first 2 weeks and 6 g/d in the last 2 weeks) or placebo for 4 weeks. Before and after BA supplementation, the athletes completed two double 30-s upper and lower limb Wingate tests, separated by 3 min. The results showed that BA supplementation significantly improved lower and upper limb total work and upper limb mean power during the Wingate test. However, there were no significant differences in lower limb mean power in the BA group when compared to the placebo group. These authors concluded that chronic BA supplementation effectively enhances high-intensity intermittent upper- and lower-body performance in highly trained judo athletes.

Creatine monohydrate is one of the most studied supplements in human performance, and its safety and efficacy are indisputable [83,84]. Studies consistently demonstrate positive ergogenic effects on single and multiple bouts of short-duration, high-intensity exercise activities, in addition to enhancing exercise training adaptations after creatine supplementation. These qualities are crucial to success in MMA [85–87]. Another proposed benefit of creatine, which is vital for sustaining the training volumes and intensities associated with combat sports, is the facilitation of glycogen replenishment. Roberts et al. [87] confirmed the ability of creatine supplementation to enhance post-exercise muscle glycogen storage during a conventional and rigorously controlled carbohydrate-loading regimen in humans. Additionally, creatine may also provide benefits for MMA athletes by mitigating the effects of traumatic brain injuries (TBI), and ongoing therapeutic applications are now being examined [88]. Doses ranging from 5 to 10 g/daily are generally recommended for enhancing performance, however research is indicating that higher doses may be warranted for the potential neuroprotective effects.

Delleli et al. [89] conducted a systematic review on the effects of beetroot juice (nitrates) on performance in combat athletes. While this review did not assess the effects of combat sports skills, it showed that nitrates may improve oxidative metabolism and force production for combat sports athletes. Effects may vary based on the population, intake duration, muscle group activated, and exercise type.

β-hydroxy-β-methyl-butyrate (HMB) is a metabolite of leucine that is formed through α-ketoisocaproate. Recently, Tartibian and Rezaei [68] demonstrated that HMB supplementation significantly improves physiological recovery markers, attenuates muscle damage, and enhances recovery by modulating cortisol, IGF-1 levels, and perceived recovery status in elite wrestlers following a simulated wrestling protocol. Durkalec-Michalski et al. [90] demonstrated that HMB supplementation significantly improves body composition and enhances both aerobic and anaerobic capacities in highly trained combat sports athletes over 12 weeks without affecting blood markers [91]. In a study by Hung et al. [92], it was found that short-term oral supplementation of three grams per day of HMB for 3 days can reduce body fat in well-trained female judo athletes undergoing energy restriction, without affecting lean body mass or exercise performance. In support, Chang et al. [93] found that HMB supplementation during acute weight loss in well-trained boxers can preserve fat-free mass and maintain heart rate response during simulated matches, without significantly affecting glucose, fat, and protein metabolism under energy restriction. The exact mechanism of action is not clear, but it is believed that HMB has an anti-catabolic effect (possibly by sparing leucine) and promotes anabolic action [94]. These anti-catabolic effects can be particularly beneficial during fight camp when training volumes and intensities are increased, and caloric intake is decreased for weight-loss purposes. The literature suggests that a dosage of 1–3 g (38–40 mg/kg) of HMB can be beneficial [94,95].

Essential amino acids (EAAs) can play a vital role in fostering muscle protein synthesis in combat athletes [96]. Essential Amino Acids cannot be synthesized de novo in humans and must be supplied by diet. Essential Amino Acids ingestion in free form in approximately ten-gram doses or as part of a protein bolus of 20–40 g after exercise are known to stimulate muscle protein synthesis [97]. From these results, consuming EEAs could increase strength and improve body composition by increasing lean body mass, and preserving lean mass during the longitudinal weight descent of the combat athlete [98].

A well-balanced diet may provide sufficient micronutrients, but combat athletes who practice rapid weight-loss or eliminate whole food groups may be at risk of nutrient deficiencies [43]. Additionally, the high training loads of fight camps and elevated energetic demands are believed to lead to an increase in micronutrient needs [48]. Supplementation with basic micronutrients may be warranted.

The sports nutrition professional may consider these supplements as part of the training practices of combat athletes. Therefore, remaining abreast of the current research will aid the sports nutrition professional in deciding which supplements have the highest efficacy and utility for the combat sport athlete. It is vital that the sports nutrition professional recommend supplements that have been third-party tested to meet label claims and be free of banned substances.

The types of weight-loss methods that are utilized prior to competition across all combat sports include: fasting, low energy intake, gradual dieting, restricting fluid intake, increasing sweat response such as heated wrestling, plastic suits, saunas, and heat exposure. Other practices commonly include taking diet pills, enemas, laxatives, and engaging in bulimia [99]. While these tactics are adopted at times, they are not endorsed by the ISSN, and the authors of this position stand. Furthermore, self-reported data show that gradual dieting and increased energy expenditure due to greater training frequencies are common in all combat sports. However, the weight-loss practices are not identical between combat sports, with the most common practices shared between boxing and MMA [99].

A primary physiological objective of fight camp is to decrease body fat. Such decreases can be advantageous for combat athletes as it may foster a greater strength-to-mass ratio, improve the endurance needed for mastering skill applications, and lead to a more effective longitudinal weight descent. Moreover, lean body mass holds more water compared to adipose tissue [100]. Therefore, maintaining or increasing lean body mass may aid in successful water manipulation and effective acute water loss strategies 24–48 h prior to weigh-in. Some combat athletes gradually reduce weight during the general preparation phase, which may be warranted if they are above the targeted 12–15% walk-around weight threshold. In this regard, athletes have started their weight descent as high as 18% above their required scale weight and successfully arrived at the weight for their division in 8 weeks as shown in Figure 1. However, this magnitude of weight descent was closely supervised by the nutrition professionals of the UFC Performance Institute and may not be advised for most athletes.

An area of emerging research involves investigating the effects of specific diets on athlete performance. The high fat diet in endurance athletes may induce metabolic adaptations [101,102], but it has been debated whether these changes improve performance [103]. In contrast, high carbohydrate diets are shown to increase short-term performance and recovery when performing repeated high-intensity activities and recovery, which is the underlying nature of combat sports [49,104,105]. Higher protein intake during the longitudinal weight descent promotes the preservation of lean body mass during caloric deficits [106]. Although protein is a vital macronutrient, higher protein intake should not compromise appropriate intake of carbohydrates and/or fat intake. Good sources of protein are lean meats such as skinless chicken, steak, eggs, fish, lentils, beans, and isolated or concentrated protein powders [43]. Ready-to-drink protein shakes and powders may have utility during fight camp for use between training sessions, since combat athletes often have several sessions a day.

Combat athletes are commonly recommended to aim for weight loss of 0.5–1 kg of body mass each week with the resulting energy deficit being based largely on total daily energy needs [38,107]. This rate of decline and the concomitant magnitude of energy deficit is contingent upon the length of the camp and how much body mass must be lost. Accordingly, the sports nutrition professional can calculate a rate of weekly weight loss based on the duration of the fight camp and the total loss in body mass that is required; then plan a systematic longitudinal weight descent.

It is advisable that the sports nutrition professional carefully monitor changes in body mass and body composition as it is common for combat athletes to lose weight too swiftly if they are not meeting their energy requirements during fight camp. This may lead to decrements in skill training, endurance, recovery, motivation, and losses in lean tissue [38].

As discussed, the Mifflin St. Jeor or Cunningham equation coupled with the levels of physical activity can be used to calculate energy needs during the longitudinal weight descent phase of fight camp. Although undesirable, if the athlete starts fight camp >15% above their desired weight class or if training camp is of shorter duration, such as <8 weeks, a greater speed and magnitude of weight loss will be required. However, due to the intense training demands during fight camp, carbohydrate intake should not drop below 3–4 g/kg/d [86,98,108]. A protein intake of 1.2–2.2 g/kg/d is advised to preserve lean tissue and aid in recovery during the energy deficit [54,106]. To facilitate an energy deficit needed for a 0.5–1 kg loss of body mass per week, fat intake is often manipulated to elicit a greater energy deficit, resulting in fat intake levels that can range from 0.7 to 1.3 g/kg/d. However, this range may need to be further adjusted to couple with TDEE. As the combat athlete’s body mass descends, subtle adjustments in energy intake may be warranted and most often a decline in energy is commensurate with the loss in body mass and/or changes in RMR that occur. Moreover, this strategy must still support the total training volume, which may include skills training and conditioning.

Tapering for MMA competition often involves a strategic reduction in training load while integrating heat acclimation, sweat sessions, and nutritional manipulation to prepare for fight week and competition. The taper period typically begins 1–2 weeks before fight week and may involve a reduction in training volume by approximately 40%. Incorporating high-intensity, fight-specific drills, helps maintain neuromuscular adaptations at an intensity sufficient to prevent detraining effects and maintain technical acuity [109,110]. Additionally, increasing heat acclimation sessions, such as using a sauna or hot bath, can enhance sweat rates, improve heat tolerance, and aid in weight management during tapering period [111]. These sessions, combined with additional sweat suit or plastic-wrapped cardio sessions, may be employed to compensate for the decreased training volume [37].

Nutritional strategies during the taper should involve a methodical decrease in calories and hydration to align with the reduced training load and manipulating macronutrients to prepare for fight week. A gradual reduction in carbohydrate intake can promote glycogen depletion and assist in weight reduction due to the water loss associated with glycogen stores [112]. Simultaneously, protein intake should be maintained to preserve muscle mass, while fat intake can be adjusted to meet caloric goals while attempting to maintain performance output [107,113]. Combining nutritional adjustments with both rapid weight loss and acute water loss strategies allows for effective weight management and readiness for fight week [37]. This tapering period and the strategies discussed will enable combat athletes to optimize their preparation for fight week and maximize their performance on fight day [22,112].

Combat athletes may engage in up to three training sessions per day during fight camp. As mentioned previously, training sessions may be brief (i.e. 45 minutes), or can be extended sessions (i.e. 90 to 120 min) of various intensities and metabolic demands [98]. Thus, planning meal frequency around the athlete’s training schedule aids in meeting carbohydrate and protein needs for the day. The ISSN’s Position Stand on Nutrient Timing details such strategies, and relevant points are summarized here. It is recommended athletes consume a meal two to 3 h prior to their first training session [97]. Strategies for acute fueling prior to training session (e.g. 60 minutes) include consuming high glycemic, carbohydrates (1–4 g/kg) while limiting fat and fiber intake to minimizing gastrointestinal distress during exercise. During high-intensity exercise, especially in hot conditions, athletes should consume a carbohydrate solution (6–8% concentration) to maintain blood glucose levels and hydration. Following a training session, consuming a combination of carbohydrates (≥1.2 g/kg/h) and protein (0.2–0.5 g/kg/h) post-training session enhances glycogen repletion and supports muscle recovery. Due to the multiple training sessions scheduled during fight camp, rapid refueling strategies may be adopted for sessions less than 6 h apart. The ISSN recommends a carbohydrate intake of 0.6 to 1.0 g/kg of body mass within the first 30 min after exercise, followed by carbohydrate intake every 2 h for the next 4 to 6 h to promote maximal glycogen replenishment. As mentioned previously, adding protein to carbohydrate intake enhances glycogen resynthesis. During fight camp, athletes focus on performance and longitudinal weight loss. This emphasizes the need for a well-planned diet that aligns with training schedules and fight weight goals.

Proper hydration is imperative for the health and performance of athletes. Even a small change of 2.5% in body weight due to dehydration can impair performance [114]. Adequate hydration should aid in supporting metabolic and training demands, reducing the risk of injury, and promoting recovery. The primary determinant of maintenance water requirement appears to be metabolic. However, total fluid requirements are highly variable and quite complex. Therefore, it is challenging to set a daily water requirement for combat athletes. Nevertheless, 1.5 ml/kcal may be suitable to cover variations in activity level, sweating, and solute load [115].

It is recommended that combat athletes focus on consuming sodium and potassium-based fluids to avoid electrolyte imbalances [98,116]. In situations where there is excessive water loss due to individual sweat rates or hot, high humidity environments, athletes may need to consume more water. For quick and complete rehydration, a simple approximation of 1.5 L of fluid per kg weight loss is recommended [111]. Fluid loss and intake must be closely monitored during a fight camp to gauge sweat rates. A good strategy to manage fluid balance is to take measurements of the athlete’s body weights preceding and following training sessions [48]. This may aid the sports nutrition professional in ensuring proper fluid replenishment and provides essential information regarding acute water loss and sweat rates that can inform weight-making tactics during fight week.

During fight camp, heat acclimation activities can be beneficial for combat athletes. The primary goal of heat acclimation is to increase the amount of sweat produced by sweat glands, thus increasing overall whole-body sweat rate [117]. Heat acclimation is induced by cumulative exposure to heat stress which in turn leads to physiological adaptations including an increase in plasma volume, increased sweat rate, increased cutaneous vasodilation and more efficient sweating over the body’s surface [118]. With habitual activation (e.g. heat acclimation), sweat glands demonstrate plasticity in their size and neural/hormonal sensitivity, which in turn impact sweat rates and sweat [Na⁺] [117]. It is of notable importance to consider that sweat rates vary amongst individuals. Generally, individuals who are heat acclimated will start to sweat earlier and will have a higher sweat rate while exercising/training. Additionally, it is commonly understood that athletes with a larger body mass and BMI will sweat more readily compared to individuals with a smaller body mass. Nevertheless, two individuals with a comparable body mass and similar exposure to heat acclimation may have differing sweat rates due to genetic distinctions, surface area-to-mass ratio, aerobic capacity, exercise intensity, and environmental conditions [119]. It should also be noted that there are seasonal adaptations in sweat rates from winter to summer, and athletes consistently living and training closer to the equatorial latitudes, particularly with high humidity, may have increased whole-body sweat rates and water loss [120]. Hence, monitoring sweat rates during fight camp can provide valuable insight into combat sport athletes’ daily fluid losses from training and/or heat acclimation activities.

Because of the limited published literature on heat acclimation and sweat rates in combat sports, the authors propose the following protocol which has been derived from methods currently adopted by combat athletes. Heat acclimation protocols can be planned during the fight camp and throughout longitudinal weight descent. Protocols should begin 4–5 weeks prior to the acute water loss phase during fight week. With respect to the proper modalities, athletes can use the sauna 3–4 times weekly for 15–25 min or hot water immersion for 20 min 2–3 times per week. Acclimation starting points and frequency of sessions will vary based on the athlete’s weight, body composition, typical fluid turnover during training, and training environment (temperature and humidity).

As with other impact sports, the prevalence of traumatic brain injuries (TBIs) in combat sports is high, particularly during fight camp when sparring and live drills are often emphasized. The causes of TBI in combat sports vary from direct impact or hits to the head, knockouts, or takedowns involving blunt force to the head [127]. TBIs range in severity and are classified as mild, moderate, or severe. Many fighters have experienced some form of TBI during their careers [127,128]. Thus, nutrition strategies implemented following TBI may aid in their recovery and timely return to sport [129,130].

Following a TBI, nutritional considerations are aimed at supporting repair and recovery, reducing inflammation and oxidative stress, neurogenesis, and restoring function [131]. As with general injury nutritional management, adequate protein and energy are paramount. Research suggests that increasing protein and energy intake in the hours following a TBI improves neurological outcomes and lowers mortality rates [132,133]. During TBI recovery, energy needs are estimated to increase between 100% and 200% of baseline resting energy expenditure values [134]. Equations to predict resting energy expenditure (Mifflin St-Jeor of Cunningham) or indirect calorimeters should be used to estimate baseline resting energy expenditure. Protein intake of approximately 2 g/kg/d total protein further supports recovery from TBI [135]. Supplementation can also aid the recovery process as well as help combat athletes consume the therapeutic doses of essential nutrients. Research suggests that creatine may have neuroprotective effects [136] by minimizing inflammation and preserving brain tissue [136]. Studies in adolescents reported improvements in cognitive function and reduced headaches, dizziness, and fatigue with creatine supplementation following mild TBI [137]. Other supplements including omega-3 fatty acids, antioxidant supplements, and B-vitamins also support brain function and are shown to reduce the severity of brain injuries [129,130]. Omega-3 fatty acids, commonly found in fish oil supplements, have anti-inflammatory properties, and may help reduce neuroinflammation [131]. Antioxidants such as coenzyme Q10, vitamin C, B vitamins and vitamin E are thought to mitigate oxidative damage following TBI [138]. N-acetylcysteine (NAC) is a precursor to glutathione, and glutathione offers neuroprotective effects from oxidative damage stemming from brain injuries [139]. Although such clinical nutritional therapies do not cure TBIs, there is compelling evidence supporting nutrition being beneficial in promoting recovery from brain injuries. Furthermore, inadequate nutritional intake impairs the recovery process.

Dietary carbohydrates are stored in skeletal muscle (350–700 g) and liver tissue (80–100 g) as glycogen and act as readily available energy reserves for glucose metabolism with final concentrations being dependent upon training status, diet, muscle fiber-type composition, sex, and body mass [146]. Glycogen is a branched polymer of glucose that binds to water at a ratio of 1 g glycogen to 2.7 g water [147]. Glycogen can contribute as much as 1–2% of skeletal muscle mass and up to 8% of liver mass [112,148]. In consideration of this, previous research has shown that 7 days of a low carbohydrate diet, combined with training and a slight reduction in energy intake (<10%), can achieve a body mass reduction of 2% while maintaining strength/power measured via a 30-s Wingate test [149]. A similar body mass loss was achieved following a 14-day period of carbohydrate restriction. Thus, due to the known association of water content with endogenous glycogen content, glycogen depletion continues to be a common means for combat athletes to reduce body mass.

A low carbohydrate diet can aid in glycogen depletion. Although combat athletes need carbohydrates for performance, adhering to <50 g carbohydrates/day during the rapid weight-loss phase prevents glycogen replenishment. The need for carbohydrates to drive high-intensity work, and its connection to body mass via glycogen status create an ongoing conflict for the combat athlete. The extent to which glycogen levels can be manipulated is primarily influenced by carbohydrate intake and the existing glycogen status before implementing glycogen-depleting strategies [150]. The rate/amount of glycogen depletion is in part predicated on the athlete’s typical carbohydrate intake, which should be calculated in grams and calories. In addition, the degree to which one can/should manipulate glycogen status is limited by the recovery window (i.e. time from official weigh-in to competition) of different combat sport disciplines and the regulations of the promotion. Care should be taken to evaluate the cost/benefit of additional exercise in the period just prior to weigh-ins versus a longer period of carbohydrate restriction prior to competition [151]. Ultimately, exercise intensity, duration, and carbohydrate feeding will dictate the rate of glycogen depletion. During fight week, training sessions typically include technique work, drills, and additional aerobic exercise, often under the auspices of the skill coach. Many skills coaches have combat athletes continue technique work and drills during fight week, which may result in greater skeletal muscle glycogen depletion due to the high-intensity nature of the activity. If the athlete is restricting dietary carbohydrates and continues high-intensity skills training, glycogen stores can be significantly depleted within hours.

Therefore, training intensity and frequencies, carbohydrate intake, and body weight should be carefully monitored to ensure an effective weight cut. Accordingly, because total calories, carbohydrates, and water may be restricted, if additional activity is needed for glycogen depletion and rapid weight loss, low-intensity steady state (LISS) cardio may have utility during fight week [151]. To achieve this, an exercise intensity ranging between 40% and 50% of maximum heart rate for 30–45 min should be suitable as an additional method for rapid weight loss. Consequently, the sports nutrition professional must work in concert with the fight week strategies of the skills coach and monitor training frequencies and intensity, exercise protocols, and losses in body mass, to perform glycogen depletion safely and effectively.

The use of bowel preparation formulas, such as those used in clinical situations to prepare the gastrointestinal tract for surgery (i.e. laxatives), is not uncommon among weight class athletes. Indeed, such tactics can be used to facilitate the removal of intestinal contents and promote acute water loss [152]. While these methods may be effective for expelling the colon of intestinal bulk, the use of clinical bowel preparation formulas (e.g. osmotic laxatives and purgatives) has been shown to reduce exercise capacity and ultimately overall performance and therefore it is not recommended [153]. Instead, dietary strategies to reduce total food volume may therefore be a preferable way to manipulate the mass of intestinal contents while maintaining performance [152].

Dietary fiber can slow the transit time of food through the bowel and draw water into the intestinal space, thereby adding bulk to stools [152]. Different foods possess different fecal bulking properties [154], and ultimately the changes in habitual fiber intake, particularly non-fermentable fibers, can elicit changes in body mass. Estimated fermentability has been shown to determine the role of fiber in total fecal wet weight. Less fermentable dietary fibers from cereals, such as wheat bran, contribute the most to total fecal weight compared to more fermentable dietary fibers, such as those originating from fruits [154]. This additional fecal matter is likely due to non-fermentable fiber’s higher water-binding capacity, as well as its greater resistance to fermentation from colonic bacteria. There appears to be a linear relationship between fiber intake and bowel cleanliness in pre-colonoscopy patients [155], and the utilization of a low-fiber diet for 2 days prior to treatment reduced bowel cleanliness compared to high-fiber diets [155]. Indeed, when a low-fiber diet (<10 g/d) was continued for 7 days, it was as effective as a bowel preparation formula [156]. In a study of 19 healthy males consuming a habitual high-fiber diet of 30 g fiber/day for 7 days followed by four of a low-fiber diet (<10 g fiber/d) that was matched for energy and macronutrients, a significant reduction in body mass was shown after 4 days of a low-fiber diet (Δ = 0.4 ± 0.91% p < 0.05) and on day 5 (Δ = 0.74 ± 0.99% p < 0.01). Subjects did report increased hunger and a decline in stool frequency; however, the diet modification was reported to be tolerated and repeatable [157].

Despite limited research on the bowel-emptying effects of a low-fiber diet, the use of low fiber diet appears to be a useful tool for reducing body mass without the need for bowel preparation formulas, which can ultimately pose a risk of undue physiological stress on the gastrointestinal system [156]. Additionally, following a low-fiber diet for a minimum of 3 days seems to be effective for rapid weight loss with minimal disruption, despite moderate increases in appetite, reductions in bowel movements, and hardening of stools. Considerations should be made to identify habitual dietary fiber intake and fiber type to better estimate and proactively account for changes in body mass when following a low-fiber diet. Furthermore, since females and older populations have reported slower GI motility, further research needs to be conducted to understand the interplay between gender and age in the effects of low fiber on body mass changes [158]. Further research is needed to establish precise guidelines for the use of low-fiber diet due to the large variations in whole gut transit times, which can range from 10 to 96 h [159]. Continued research on the implications of low-fiber diets in weight-making sports, as well as health and performance outcomes, is warranted.

As combat athletes lose water and electrolytes through thermoregulatory sweating during heat exposure, aerobic activity, and skills training during fight week, it is well established that the rate and composition of sweat can vary significantly within and between individuals [160]. Scientists and practitioners may conduct sweat tests to determine sweat and electrolyte losses, particularly sodium. However, the current methodological practices and challenging field conditions often lead to inconsistent and inaccurate results. While techniques like whole body washdown, which is the reference standard, require a laboratory, more practical methods such as sweat patches have shown inconsistency and limited effectiveness [160].

Accordingly, determining how much sodium to ingest or restrict during fight week proposes numerous challenges. To establish a measure of sodium restriction, it is advisable that the sports nutrition professional first ascertain a baseline of sodium intake during fight camp and then propose a lower sodium intake of < 2.3 g daily during fight week, if needed. Due to increases in sweat loss, athletes should not consume less than the current RDA of 2300 mg/day in order to minimize sodium losses [161,162]. Thus, for athletes whose base intake is below 2300 mg, more emphasis can be put on other water manipulation modalities. Physiologically, the human body tightly regulates the osmotic pressure of body fluids through renal excretion and retention of electrolytes and fluids. A summary of literature examining the relationship between sodium intake and water intake found that in a steady state, urine volume remains unchanged over a broad range of sodium intakes. Rather, the adaptation to higher sodium excretion lies only in changes in urinary sodium concentration [163].

Water retention is responsible for the well-documented increase in body mass following acute increases in sodium intake [163]. The resulting increase in fluid intake due to thirst in conjunction with no significant changes in urine volume causes the extra fluid to remain in the body to limit the rise in plasma sodium concentration by diluting the sodium that cannot be excreted quicky enough [163]. In a steady state, if sodium levels remain within a reasonable range of (50–250 mmol/day), most of the observed adaptation will rest on changes in the concentration of sodium in the urine without any changes in urine flow rate. However, when an abrupt change in sodium occurs (e.g. 70 mmol/d to 250 mmol/d), assuming usual daily activities remain constant and without any limitations in water intake, a return to sodium and body mass balance requires 2–3 days [164].

The complexity of sodium steady state dynamics and its relationship to body mass changes is further complicated by the varying tactics utilized by combat athletes such as hyperhydration (water loading), heat acclimation, caloric restriction, diuretics, etc., during the weight-cutting period [116,143,165,166]. Despite the limited body of research on varying sodium levels and their effects on acute water loss, sodium restriction has become a common practice among some combat athletes during the weight cutting period [98]. Due to the limitations in previous research aimed at investigating the role of sodium restriction on acute water loss in combat athletes, the precise degree to which sodium needs to be reduced is unknown. Further research is warranted.

Urine excretion is tightly regulated by the renal system. Fluid balance is achieved by aldosterone and anti-diuretic hormone triggering a renal response to either release or conserve fluid thereby maintaining total body water as well as electrolyte balance [167]. Urine excretion is the body’s primary fluid balance regulator and as such, typical urine losses range from 1–2 liters per day [168,169]. Urine volume decreases with dehydration, with the obligatory rate of urine production to excrete metabolic waste being 0.5 liters per day [167,170]. The upper limit for urine production is 1.8 liters per day; therefore, fluid intake that exceeds urine production limits may lead to hyponatremia [171].

To encourage polyuria and thus acute water loss, the use of pharmacological diuretics to promote greater urine loss has been reported among combat athletes [166]. In a survey of 637 combat athletes, the prevalence of reported diuretic use was 12% overall, with the lowest reported use in judo of 5% and highest of 12% in Tae Kwando [143]. The survey did not specify the type of diuretic used which may include pharmaceutical grade diuretics and/or over-the-counter products such as caffeine anhydrous. The lower prevalence of diuretic use may in part be due to the increase in testing and regulatory bodies that monitor athletes given that pharmacological diuretics are included in the World Anti-Doping Agency’s List of Prohibited Substances [172].

A commonly adopted method for inducing polyuria amongst combat athletes is water loading or hyperhydration. Previously, water-loading practices in combat sports had been largely based on anecdotal evidence. Athletes and sports nutrition professionals prescribed varied recommendations for total fluid consumption and the durations in which water loading should be applied. To date, there is not a robust body of research on the subject. Water loading is a strategy characterized by the consumption of large volumes of fluids for several days prior to fluid restriction. A rapid weight-loss questionnaire of 314 mmA athletes showed that the frequency of water loading occurred “always” or “sometimes” in 72.9% of the athletes surveyed [173]. Barley et al. examined acute water loss habits in 637 combat athletes and revealed a water-loading prevalence of over 60% in MMA, Muay Thai, kickboxing, and boxing, with an overall prevalence of 53% among all combat sports [143].

A study which provided significant insight on the efficacy and safety of water loading was conducted by Reid et al. [109]. They investigated the effect of water loading for 3 days (100 ml/kg/d) compared to a control group (40 ml/kg/d), followed by fluid restriction on day 4 (15 ml/kg/d). Significant body mass loss was observed in the water-loading group on day 5, with a loss of 3.2% compared to 2.4% in the control (CON) group [116]. The difference in body mass loss in the water-loading group was attributed to greater fluid loss relative to fluid intake during the period of fluid restriction, compared to the control group. Despite concerns regarding hyponatremia, the study showed no evidence of problematic blood chemistry changes or impaired physical performance following rehydration. Moreover, a 3.2% loss in body mass represents nearly half of the 6.7% above scale weight at 72 h prior to weigh-ins.

Another study conducted by Cho & Han [174] included 13 university wrestlers (weight 71.5 ± 8.0 kg, BMI 25.0 ± 2.0 kg/m²) randomly divided into the weight loss (WL) group (n = 6) and water-loading weight loss (WWL) group (n = 7). Wrestlers performed a two-week weight-loss program, targeting an average of 5–10% of body weight reduction, under the supervision of a coach. Participants were instructed to drink 1.5–2 liters and 6–7 liters in the weight loss and water loading weight loss groups, respectively, for two weeks prior to weigh-in. Neither group consumed water the day before weigh-ins. Anthropometric characteristics, hematocrit (HCT), serum electrolytes, aldosterone, and cortisol were measured before and after weight loss. Results showed the weight-loss and water-loading weight-loss groups showed a decrease in body mass of 8.2% and 11%, respectively. These numbers supersede the 2.4% and 3.2% loss in body mass observed by Reid et al. [109]. However, it must be considered that the wrestlers underwent approximately eleven additional days of water loading, caloric deficits, and intense training. Hence, the total loss in body mass of 8.2% and 11% also includes changes in body composition. Of notable importance, there were no negative implications on blood chemistry and the researchers concluded that large-volume hydration before water restriction for short-term loss in body mass can be completed safely under the parameters with which this study was conducted.

The manipulation of body mass via sweating is the most common method of rapid weight loss undertaken by combat athletes [152]. Although sweat losses are commonly used, there are currently no generalized standards to determine the ideal method, the optimal duration of exposure, and the most suitable environmental factors. However, acute water loss strategies must be applied while minimizing overheating and adverse performance and health outcomes.

Despite previous research suggesting that combat athletes lose nearly 10% of their total body mass pre-weigh-in [107,141,165,166,175,176], solely utilizing sweat loss to achieve a 10% decline in body mass within 24 h of weigh-in is ill-advised and potentially dangerous to health. With several factors notwithstanding, body mass losses ranging from 5% to 8% can have varying degrees of impact on health and performance. Some data indicate that certain athletes can achieve this decline in body mass via acute water loss and not compromise performance and health [166]. Nevertheless, to date, this remains inconclusive.

A major challenge is understanding which acute water loss methods should be utilized to achieve the decrease in body mass leading to weigh-ins; and what is the true starting point to initiate acute water loss tactics. The starting point prior to acute water loss should represent body mass in a euhydrated and well-nourished state (i.e. prior to glycogen and fiber depletion) to take advantage of non-essential compartments of bound water.

In a research study that captured weight loss data in 600+ successful UFC athletes’ weight cuts, it was shown that there was a significant reduction in non-essential body mass in the 24–72 h window prior to weigh-ins. UFC fighters were approximately 6.7% above their weight class 72 h before weigh-ins, but were only 4.4% over their weight classes 24 h prior to weigh-ins [177]. Although the hydration status in the 24-h window before weigh-ins was not published, a 4.4% body mass loss represents a much smaller and therefore feasible amount of acute water loss.

It has been noted that when women and men were matched for surface area-to-mass ratio and fitness level, both had similar heart rate and core temperature responses to heat acclimation. Despite this, sweating responses were greater in men, and they required a shorter heat acclimation period (4–5 days) compared to women [118]. With the growing number of female participants in combat sports, it is important to consider key differences in sweat rate and heat tolerance. Female thermoregulatory responses vary throughout the menstrual cycle due to the influences of reproductive hormones estradiol and progesterone. During the luteal phase or high hormone phase of oral contraceptive use, thermoregulatory control of both sweating and cutaneous vasodilation is shifted by approximately 0.5 Celsius to higher core body temperatures [118]. In hot and dry conditions, males experience a smaller change in core temperature compared to women, whereas the opposite is true in hot and humid climates. Men have a higher overall sweating capacity, which allows them to respond more efficiently to dry heat [118]. It is worth noting that women have a lower sweat capacity than men for a given amount of metabolic heat generation, and they are also less responsive to the effects of training adaptation on sweat rate and sweat temperature threshold [118]. Women between 18 and 35 years of age are also five times more likely to experience symptoms associated with orthostatic intolerance compared to men of the same age and health status [118]. Despite these differences in sweat rate and adaptations, the role of sex hormones in thermoregulation and acute water loss (adaptive whole-body heat loss) is complex, and further research is needed.

The prevalence of sweat loss strategies for acute water loss is not surprising considering the relatively large body mass losses that can be achieved in a rapid and time-efficient manner, with sweat rates up to two liters per hour having been recorded [168]. The onset of sweating can be altered by changes in plasma electrolyte concentration, plasma volume, and total body water content. However, these factors are not optimized to enhance sweat losses without the introduction of more fluid into the body, which is contrary to the end goal of acute water loss [152].

Variables that may dictate the rates and volume of acute water loss includes:

Generally, acute water loss strategies can be classified into two categories: active sweating (exercise or skill training often with the aid of a sauna suit or layered clothing for insulation) or passive sweating (exposure to hot environment, e.g. sauna, steam rooms, infra-red saunas, wraps and/or hot baths). It is important to note the differences in physiological response to active versus passive sweating. Cutaneous vasodilation and sweating during heat stress results in a redistribution of blood flow to the periphery and a requirement for increased cardiac output to meet the thermoregulatory demand. Passive sweating prior to active sweating decreases plasma volume, sweat rate, and body heat storage [179]. These physiological changes occur to a lesser extent when hypohydration develops only during exercise [179]. When combat athletes are in a very depleted and hypo-hydrated state, they may need to limit active sweat loss methods. During exercise, the mismatch between venous return and limited cardiac output is mitigated by the muscle pump which propels blood back to the heart. The lack of muscle pump or sudden cessation of exercise in addition to increased peripheral venous compliance can result in a transient decrease in cerebral perfusion pressure causing orthostatic intolerance, dizziness, fatigue, and syncope [118].

Traditionally, many combat athletes make use of combining training sessions (active) with fluid restriction to promote dehydration. Active sessions are often used with additional passive methods for acute water loss. Tangible arguments for, and against, active strategies can be made. Active strategies such as high-intensity skills training, shadow boxing and striking pads require increased energy expenditure and oxygen demand which in turn generates more heat, leading to an increase in sweat rate to compensate and cool the body. This can result in the athlete accumulating considerable acute water losses. Additionally, many skills coaches practice active methods, such as striking and technical sparring, with the notion that this maintains the motor skill applications which were advanced during the general preparation and fight camp periods. Moreover, the increased loss of peripheral skeletal muscle glycogen associated with active methods such as hitting pads and striking, may further contribute to water loss. If the combat athlete has greater than the average of 4.4% body mass to lose within 24 h of the official weigh-in, both active and passive strategies may be warranted in some situations. Nonetheless, as discussed, reduced plasma volumes from acute water loss can alter changes in cardiac output, flow, distribution, and blood pressure, which in turn can impair the efficiency and safety of active methods such as skills training and technical sparring [118].

It is of notable importance that many coaches, fighters and teams have established methods for acute water loss and the sports nutrition professional may have to operate within the preferred parameters of these strategies. As an example, if the team uses active methods and several skill application sessions as part of acute water loss methods, then passive strategies should be used only when required and when ample time is available for recovery. As with all nutritional strategies in combat sports, particularly as it pertains to acute water loss requirements, the sports nutrition professional is often required to evaluate what is optimal and what is necessary.

Passive strategies may allow the combat athlete to spare muscle glycogen and reduce the elevated physiological demands which active strategies may induce on both the nervous systems and skeletal muscles. The frequency and duration of passive strategies will be contingent on how much body mass must be reduced within 24 h of weigh-in. Passive strategies, as with all acute water loss methods, may be appropriate when sufficient post-weigh-in recovery time is available. Nevertheless, passive strategies must be strategically applied to optimize the volume and rate of acute water loss [166]. It is also prudent that the sports nutrition professional ensures that combat athletes do not overheat from passive strategies for acute water loss. Monitoring the athletes core temperature is a method to avoid overheating, heat stress injuries or potential hyperthermia. The core temperature in which such conditions may occur is not exact and highly variable between individuals. However, hyperthermia is defined as a body temperature greater than 40° Celsius (104° Fahrenheit) [180]. Therefore, independent of the cumulative exposure to heat acclimation the combat athlete has undertaken, it is imperative to avoid heating near this core temperature. As with all acute water loss strategies, the pros and cons are contingent upon any contraindications, the coexisting practices, and the demands of the combat athlete.

In general, passive weight cut strategies refer to those modalities in which combat athletes undergo exposure to heat for acute water loss. These strategies are most often done without extensive physical activity.

The allotted recovery window between weigh-ins and competition dictates the magnitude of acute water loss. As noted, several combat sports disciplines require same-day weigh-ins with limited recovery windows. Olympic sports such as wrestling and Tae kwon do are such examples, as well as most of the governing bodies regulating jiu-jitsu competitions. Accordingly, rapid weight-loss strategies have diminished value to the athlete when the window of time available to replenish fluid and electrolyte losses is less than 4 h. Moreover, sports such as Brazilian jiu-jitsu and wrestling may have an athlete on the mat well within 2 h of their official weigh-in, depending on their weight class and how the competition is structured. As such, recovery windows that are short make it harder for meaningful rehydration and refueling to occur if excessive weight cuts are adopted. Therefore, careful planning to maintain an appropriate weight during the general preparation phases becomes of greater significance. Moreover, the longitudinal weight descent must be carefully designed to allow the athlete to decrease as much body mass as possible via changes in body composition and reductions in body fat. It is imperative to have the proper planning of total calories and macronutrient distributions coupled with training volumes. Based upon anecdotal observations from the authors working with thousands of combat athletes, below are recommended percentages of body mass loss that may be most appropriate for varying lengths of time between weigh-in and competition.

Carbohydrates are critical for the high-intensity nature of combat sports. Due to the practice of glycogen depletion prior to weigh-in to facilitate rapid weight loss, glycogen restoration following weigh-ins is desired [6]. Post weigh-in nutrition should include adequate carbohydrate content to at least fuel the athlete for the competition and maximize glycogen stores. Glycogen restoration must be carefully balanced and introduced at a tolerable rate to reduce gut discomfort while being at a low enough energy density to not hamper gastric emptying during the initial rehydration phase [194]. For this reason, an oral rehydration solution with a 2–3% carbohydrate (e.g. 15 g/500 ml) solution is more appropriate during rehydration for hypohydration >3% of body mass, whereas sports drinks with a ~ 5% carbohydrate (e.g. 25 g/500 ml) solution is well tolerated for hypohydration <3% of body mass.

With the initial oral rehydration solution and then solid foods, post weigh-in carbohydrate intake totaling 8–12 g/kg is appropriate for combat athletes that underwent significant glycogen depletion to facilitate rapid weight loss prior to weigh-ins. This range of carbohydrate ingestion is suitable for maximizing liver and skeletal muscle stores. However, if greater glycogen depletion has not occurred then aggressive carbohydrate intake is not necessary, and combat athletes may simply adopt a more moderate post weigh-in carbohydrate intake ranging 4–7 g/kg [6].

Strategies to meet carbohydrate needs post weigh-in include high glycemic index carbohydrates [197] and the use of carbohydrate rich fluids to simultaneously meet total fluid needs while facilitating glycogen restoration [6]. When ingesting carbohydrates at a rate of >60 g/h, incorporating food/fluids/supplements with a varied carbohydrate source (e.g. glucose and fructose) facilitates carbohydrate absorption via multiple gut transport mechanisms [198].

Post weigh-in intake should prioritize optimizing nutritional status while avoiding GI distress. Of the many dietary modifications used to elicit rapid weight loss, a low residue diet has the most benign impact on performance and health [157]. In addition, fiber has a minimal contribution to energy needs and reduces gastric emptying/absorption rates and therefore the rapid reintroduction of fiber can cause discomfort [199] Fiber intake post weigh-in contraindicated for optimal post weigh-in recovery and should be limited. Protein and fat intake should be managed in the post weigh-in protocols as large boluses may also delay gastric emptying.

In addition, gastrointestinal distress following weigh-ins can be limited by avoiding trigger food/beverages during the acute rehydration phase (0–2 h following weigh-ins). Currently, no literature on specific foods that cause GI distress in combat athletes exists. However, certain foods are associated with gastrointestinal distress in both the general population and athletes [200,201]. Thus, the authors suggest avoiding or minimizing these foods: