Spanish Nutrition Society's agreed guidelines on nutrition strategies for sports

The importance of CHO in endurance sports has been widely demonstrated. Adequate storage of muscle and liver glycogen allows athletes to maintain high intensity for prolonged periods and significantly delays fatigue. CHO-loading strategies before long competitions (carbo-loading) can increase muscle reserves by up to 50%, improving performance in events lasting > 90 min []. ²⁵

During exercise, the intake of exogenous CHOs maintains plasma glucose availability, preserves muscle glycogen, and helps support brain function, reducing perceived effort and the risk of "bonking" or "hitting the wall" []. For efforts lasting between 1 and 2.5 h, CHO intakes of 30–60 g/h are recommended []; however, in longer-duration events, such as marathons or ultra-trails, it has been shown that consuming between 90 and 120 g/h maximizes CHO oxidation, improves performance, reduces exercise-induced muscle damage, and speeds up the recovery of sprint capacity and neuromuscular function [,,]. However, it is essential to train the digestive system ("gut training") to avoid gastrointestinal discomfort, which can compromise the performance and tolerance of the nutritional plan []. ^{19 1 21 22 23 24}

Although CHO demands in strength and power sports are not as high as those in endurance sports, muscle glycogen is essential for repeated explosive efforts and maintaining training quality []. Adequate CHO availability, glycogen resynthesis between sessions, improves work capacity, and can enhance strength and muscle hypertrophy by enabling training with higher volumes and intensities []. ^{93 2}

Team sports are characterized by intermittent high-intensity efforts, alternating with incomplete recovery periods. In this context, muscle glycogen is crucial for sustaining sprint capacity, agility, and cognitive performance throughout the match []. ⁷

CHO consumption before and during the match helps maintain optimal glucose levels and delays fatigue, especially in the final stages of the competition. Intakes of 30–60 g/h during the match have been shown to be effective for maintaining technical and tactical performance [,]. ^{7 94}

CHO intake planning should be tailored to the type of sport, seasonal phase, and training load. On a daily basis, recommendations vary according to the volume and intensity of the exercise. For light or technical sessions, consumption of 3–5 g of CHO per kg of body weight per day is suggested, while moderate-intensity training (1–2 h/day) requires between 5 and 7 g/kg/day. For prolonged or high-intensity training sessions (2–3 h/day), requirements may increase to 7–10 g/kg/day, and during specific loading phases before long competitions, an intake of up to 12 g/kg/day may be achieved []. ²⁵

For tests lasting longer than 90 min, it is recommended to carry out a CHO load involving an intake of 8–12 g/kg/day for 36–48 h prior to the event, accompanied by a progressive reduction in training volume and intensity to maximize muscle glycogen availability []. ²⁵

During exercise, CHO needs depend on the duration of the effort. For activities lasting less than one hour, exogenous intake is usually not necessary. However, when exercise lasts between 1 and 2.5 h, it is recommended to consume 30–60 g of CHO per hour. For efforts longer than 2.5 h, intake can reach 90–120 g/h if combinations of different types of CHO (such as glucose and fructose) are used to increase the rate of exogenous carbohydrate oxidation and reduce gastrointestinal discomfort [,,]. ^{21 22 23}

The recovery phase after physical exercise is also important, especially when performing double sessions or intense workouts on consecutive days. In these cases, it is recommended to consume 1–1.2 g/kg/h of CHO during the first 4 h after exercise. Additionally, combining this with proteins (approximately 0.3 g/kg) has been shown to enhance protein synthesis and accelerate muscle recovery []. ¹⁰¹

From a practical standpoint, it is essential to train the gastrointestinal system to tolerate HCD during exercise, a strategy known as gut training, which should begin with moderate doses (30–60 g/h) and be progressively increased. The choice of CHO source should be adapted to individual preferences and tolerances, and gels, isotonic drinks, bars, or other combined forms should be used. Similarly, it is recommended to integrate CHO intake with adequate hydration to facilitate absorption and prevent dehydration.

Ultra-endurance athletes adapted to LCD for prolonged periods (>9 months) have been shown to maintain a capacity for glycogen storage and utilization similar to that observed in athletes on HCD, while their maximum rates of fat oxidation can double []. These results have led to the consideration of the LCD as a potential option for ultra-endurance sports in which glycogen preservation is critical. ¹⁴

However, it has been reported that this increase in lipid-dependence increases the energy cost of exercise and reduces mechanical efficiency, which can negatively impact events that require high submaximal intensities or decisive final sprints [,]. ^{12 44}

In recreational runners and cyclists, some studies have not observed significant differences in submaximal performance after LCD; however, benefits have been reported in the reduction in fat mass and glycemic control parameters [,]. These findings suggest possible usefulness during the pre-season phases or periods focused on improving body composition. In contrast, in elite runners, the LCD has shown negative effects on running economy and performance during competitive events, confirming that adequate CHO intake remains crucial in situations of high glycolytic demand [,]. ^{31 32 33 44}

Performance in strength and power sports largely depends on the availability of muscle glycogen, which is essential for brief and explosive effort. LCD can limit the ability to perform multiple high-intensity repetitions and decrease power output [,]. ^{34 35}

Some studies have indicated that, although no significant decrease in maximum strength is observed if protein intake is adequate, the ability to maintain performance over repeated sessions may be compromised []. ³⁶

In athletes who need to rapidly reduce body weight, the LCD can be useful, as long as protein intake (≥1.6 g/kg/day) is maintained and it is strategically planned [,]. ^{37 38}

Team sports combine intermittent effort with rapid and repeated high-intensity transitions. In this context, adequate CHO availability is critical for sustaining sprint capacity and recovery between actions []. ³⁹

LCD in basketball and football players has shown decreases in the total work performed, as well as alterations in anabolic hormones and bone remodeling parameters. This can affect competitive performance and increase the risk of injuries and long-term bone health issues, particularly in young and developing populations [,]. ^{32 38}

In sprint sports, maximal power output relies heavily on phosphocreatine and fast glycolysis. The reduced glycogen availability typically induced by LCD can compromise repeated sprint ability, neuromuscular drive, and total work performed [,,,]. LCD may be useful only during short body-composition phases, during high-intensity training blocks. However, sufficient CHO availability is essential to maintain peak power and technical execution [,,]. Therefore, LCD in sprinters should be temporary, carefully controlled, and never coincide with key intensity sessions. ^{34 35 39 93 36 37 38}

Aesthetic athletes often face chronic pressure to maintain low body mass, which increases the risk of LEA, menstrual dysfunction, and bone-turnover disturbances [,,]. Because LCD tends to reduce total energy intake and limit glycogen availability, it may impair training quality, technical skill acquisition, and recovery during long technical sessions. Their restrictive nature can exacerbate LEA and RED-S risk, making LCD generally unsuitable in aesthetic sports, except possibly in brief, closely monitored off-season phases. ^{96 97 98}

Athletes in weight-category sports frequently use LCD for rapid weight manipulation. Although such approaches can produce short-term reductions in body mass, they may simultaneously impair high-intensity performance, hydration, and recovery [,,]. Glycogen depletion reduces strength, power, and repeated-effort capacity—key components in combat sports and lightweight rowing. If used, low-CHO phases should be brief, medically supervised, and followed by controlled CHO reintroduction before competition. ^{37 38 99}

The KD has been shown to significantly increase fat oxidation during submaximal exercise (~1.5 g/min), even in trained athletes, which could be useful in very long-duration events in which glycogen preservation is crucial [,,,]. However, studies on elite athletes have shown a decrease in performance, especially at submaximal and high intensities, owing to the increased energy cost associated with using fat as the main source of energy and the lower availability of muscle glycogen []. ^{29 48 50 51 28}

A recent systematic review concluded that although improvements in fat oxidation are observed, there is no clear evidence of benefits in oxidative performance, and in some cases, negative effects have been documented. Furthermore, most studies reporting these negative effects lasted less than six weeks, and it is unknown whether longer adaptation periods could modify these results [,,]. ^{28 48 49}

KD tends to have neutral or even negative effects on the maximum strength and strength gains compared to diets with higher CHO content. CHO restriction reduces the ability to replenish glycogen, compromising performance in short and explosive efforts that depend primarily on this substrate [,]. ^{28 107}

A systematic review showed that, in strength and power training, the KD did not provide significant advantages, and several studies observed reductions in power and anaerobic capacity [,]. ^{49 107}

However, some individuals may tolerate the diet without major changes, highlighting the importance of individual variability and the need for a personalized approach []. ²⁸

In team sports, such as soccer or basketball, where intermittent high-intensity efforts are combined with periods of incomplete recovery, the KD may not be optimal. A study on semi-professional soccer players showed that after 30 days on a KD, the players reduced their fat mass without affecting their muscle mass, strength, or power. However, specific performance in competition has not been evaluated, and maintaining lean mass does not necessarily imply the preservation of anaerobic capacity or repeated sprint ability []. ⁴³

The reduction in glycogen levels could affect the ability to perform repeated high-intensity efforts, a fundamental characteristic of team sports. Therefore, although it may be useful for rapid weight loss, its application during competitive phases should be approached with caution and tailored to individuals.

KD significantly reduces glycolytic flux and glycogen availability, both of which are essential for maximal power and repeated sprints. Evidence consistently shows impairments in high-intensity exercise economy, anaerobic capacity, and power production under ketogenic conditions [,,,,]. Although KD increases fat oxidation, this adaptation has no ergogenic value for sprint events. Consequently, KD is not recommended for competitive sprint athletes. ^{28 49 50 51 93}

KD may facilitate short-term reductions in fat mass, but its restrictive nature increases the risk of LEA, micronutrient deficiencies, and hormonal disturbances in aesthetic sports, where RED-S prevalence is already elevated [,,,,]. Reduced glycogen availability may compromise movement precision, explosiveness, and overall training quality. KD should therefore only be considered in very short, supervised blocks for body-composition management and not during technical or competitive periods. ^{96 97 98 99 100}

KD is sometimes adopted to induce rapid weight loss, but the associated glycogen depletion reduces hydration status and total training capacity, increasing the risk of performance decrements in combat sports and rowing [,,]. Reduced anaerobic output is particularly detrimental during decisive high-intensity exchanges. Although some athletes tolerate KD without large losses in lean mass, structured CHO refeeding before competition is essential to minimize negative impacts on performance. ^{28 43 49}

IF, especially in its TRF form, appears to have positive effects on endurance sports. Improvements have been observed in VO, cardiac output, and muscle oxidative capacity, which translate into greater utilization of fatty acids as fuel and preservation of glycogen reserves [,]. 2max ^{55 62}

The activation of AMPK and regulation of sirtuin-1 induced by fasting promote muscle adaptations that optimize metabolic efficiency and aerobic capacity [,]. Similarly, IF is associated with a reduction in systemic inflammation, an improvement in the power-to-body weight ratio, and a decrease in total fat mass, which are key factors in endurance sports []. ^{16 54 16}

A study of elite cyclists showed benefits in body composition and performance parameters after an 8-week TRF protocol without compromising strength or power []. ¹⁶

In high-intensity disciplines that rely primarily on CHO availability, IF has shown mixed results. Some studies have documented a decrease in speed and power attributed to lower glycogen availability and a possible reduction in protein synthesis during periods of energy restriction [,,]. ^{56 63 64}

However, other studies did not report significant changes or even showed that performance was not negatively affected after a minimum adaptation period (at least four consecutive days) [,,]. This suggests the existence of an individual adaptation phase, in which the body adjusts to a new energy pattern. ^{57 58 64}

It is important to note that most available studies focus on short-term interventions, so there is no conclusive data on the long-term impact of IF on strength and power performance []. ⁶⁴

The effect of IF on team sports, which are characterized by intermittent and high-intensity efforts, has been less studied and presents mixed results. Part of the controversy comes from the extrapolation of studies conducted during Ramadan, where abstinence from fluids is also imposed in addition to dietary restrictions. During Ramadan, a decrease in physical performance was observed, which was mainly attributed to dehydration and disruption of circadian rhythms []. ⁵⁹

Although the definition of IF and fasting during Ramadan may seem similar, in practice, they differ in key aspects, such as the possibility of drinking water and the distribution of meals, so the results are not directly comparable.

Sprint athletes depend on maximal glycolytic output, which can be compromised by fasted states that reduce glycogen availability and impair power production [,]. IF has been associated with decreased training intensity and neuromuscular output in high-intensity sessions unless feeding windows are carefully timed [,,]. Therefore, IF is generally unsuitable on days involving speed development, sprint mechanics, or explosive power work. ^{56 63 57 63 64}

In aesthetic sports, IF increases the risk of LEA, disrupted menstrual function, hormonal dysregulation, and impaired bone turnover—issues that are already prevalent in this population [,,]. Prolonged fasting may also impair concentration, fine motor control, and technical skill acquisition during long rehearsals. IF should be considered only in highly controlled situations, with strict monitoring of energy availability, micronutrient intake, and recovery. ^{96 97 98}

IF is sometimes used to facilitate weight reduction in weight-category sports, but extended fasting windows may compromise training intensity and recovery during combat-sport preparations or rowing [,]. Its catabolic potential increases the risk of lean-mass loss and reduced power output—both detrimental in these disciplines. If implemented at all, IF should be scheduled early in the preparation period and discontinued close to competition to preserve high-intensity performance. ^{59 61}

In endurance sports, some studies have suggested that vegetarian diets can improve aerobic capacity by increasing the consumption of antioxidants and complex CHO and lowering energy density, which facilitates weight and body composition control []. Additionally, a higher intake of polyphenols and other bioactive compounds may reduce oxidative damage and exercise-induced inflammation []. ^{15 11}

In strength and power sports, the main challenge is to ensure adequate total protein intake and sufficient leucine levels to stimulate muscle protein synthesis. Although the leucine content is usually lower in plant-based sources, strategies such as increasing the total amount of protein or using supplements (soy, pea, or rice protein) can compensate for this difference [,,,]. ^{66 71 72 75}

Evidence regarding team sports is scarce, although no significant differences in performance have been reported between vegetarian and omnivorous athletes []. Proper planning is key to ensuring sufficient energy supply and preventing muscle mass loss during long seasons or periods of highly competitive load. ⁶⁹

Sprint performance is sensitive to creatine, carnosine, and leucine availability—nutrients that are typically lower in VEG patterns. Inadequate intake may reduce buffering capacity and repeated sprint ability [,,]. However, with optimized protein distribution and appropriate creatine and beta-alanine supplementation, sprint athletes following VEG can maintain performance. Ensuring sufficient total energy intake is critical to avoid LEA during high-intensity phases. ^{66 71 72}

VEG may offer high micronutrient density and antioxidant benefits, but the risk of LEA, iron deficiency, and suboptimal protein intake is notable in aesthetic athletes [,,]. Careful planning is essential to maintain bone health, hormonal function, and motor coordination—all critical in gymnastics and figure skating [,,]. Supplementation with vitamin B12, vitamin D, calcium, and omega-3 is often necessary. ^{68 71 75 96 97 98}

VEG can support weight regulation because of their high fiber and low energy density, but athletes must avoid excessive restriction, which increases LEA and decreases power output [,,]. Ensuring adequate protein, iron, and zinc intake is essential to preserve strength during weight-cut phases. Creatine supplementation is particularly beneficial in vegan and vegetarian fighters and rowers []. ^{70 71 75 66}

In vegetarian athletes, protein intake should be at the upper end of the general recommendations for athletes (1.6–2.0 g/kg/day) to compensate for the lower digestibility and protein density of plant-based foods. The distribution of proteins throughout the day and inclusion of leucine-rich sources are key strategies for optimizing protein synthesis []. ¹¹⁰

Such as alpha-linolenic acid (ALA), found in chia seeds, flaxseed, and walnuts, can be converted into eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), although this conversion is limited. Microalgae-based supplements can be considered to ensure adequate intake of these fatty acids []. ¹¹¹

Vitamin B12 is critical and should be supplemented by everyone who follows VEG. Deficiency can have serious consequences for health and performance; therefore, it is advisable to monitor its levels [,]. ^{66 75}

Vitamin D is often insufficient in vegan athletes, especially during winter or in indoor sports. It is recommended to assess supplementation on an individual basis and ensure adequate intake of calcium-rich plant-based sources [,]. ^{73 74}

Non-heme iron from plant sources has lower bioavailability. Therefore, it is recommended to include a variety of iron-rich foods and improve their absorption by combining them with sources of vitamin C while avoiding phytates, tannins, and calcium in the same meal. Similarly, the limited bioavailability of zinc makes it necessary to incorporate foods rich in zinc and use cooking techniques that enhance its absorption []. ⁷⁵

Iodine is another critical nutrient, especially for people following a vegan diet. In general, the use of iodized salt is sufficient to meet daily requirements. It should be noted that excessive iodine intake from seaweeds can be harmful [,]. ^{72 75}

Creatine and beta-alanine, found almost exclusively in animal products, might be of particular interest to vegetarian and vegan athletes who practice strength or power sports. Supplementing with them can help improve anaerobic capacity and recovery []. ⁶⁶

It is essential to regularly monitor nutritional status through blood tests and body composition assessments. Planning and support by a specialized dietitian-nutritionist are fundamental to ensuring the success of this type of dietary strategy.

PALEO presents significant limitations for endurance sports owing to its low CHO content, which compromises glycogen resynthesis and reduces the availability of energy substrates during prolonged exercise []. Although it has been suggested that their high nutritional density and antioxidant content could promote certain mitochondrial adaptations, the evidence indicates that excessive CHO restriction may impair performance in events lasting more than 60–90 min [] ^{81 44}

Some nutritional periodization models may integrate periods of low CHO availability to promote metabolic efficiency, but rigidly applying this strategy throughout the season does not appear to be compatible with maintaining performance in endurance sports []. ¹¹⁵

In these disciplines, PALEO could offer benefits in terms of body composition and muscle recovery owing to its high protein content and healthy fats [,]. However, the low availability of CHO can limit performance in repeated high-intensity efforts and rapid replenishment of glycogen post-training, especially in routines with high frequency or volume. ^{85 114}

Some theoretical studies have suggested that this diet may be useful during the cutting phases or for body weight control, but its ergogenic impact on strength athletes is still poorly documented in well-controlled trials []. ¹¹⁵

Team sports have a high glycolytic demand owing to a combination of intermittent efforts. A study conducted by Pięta et al. (2023) on professional handball players subjected to a PALEO intervention for 8 weeks showed a significant reduction in body mass and improvements in some metabolic markers, such as adiponectin []. ⁸²

However, a similar study observed a decrease in total work performed and in average and maximum anaerobic power, suggesting that PALEO may not be optimal in sports contexts that require high glycogen availability to maintain explosive actions and rapid recovery between efforts []. ⁸³

The relatively low CHO availability characteristic of PALEO may reduce glycolytic capacity and impair repeated sprint performance [,,]. Although PALEO provides high-quality proteins, insufficient CHO supply limits neuromuscular output and rapid phosphocreatine resynthesis. Sprint athletes, therefore, require strategic CHO inclusion around high-intensity sessions if PALEO is used. ^{81 82 83}

PALEO's exclusion of grains and dairy can increase the risk of deficiencies in calcium, vitamin D, and CHO—nutrients essential for bone health, hormonal function, and high-quality technical training [,,,]. The restrictive nature of this diet may exacerbate LEA risk in athletes who are already vulnerable to RED-S. PALEO thus requires careful adaptation to ensure adequate energy and micronutrient intake in aesthetic sports. ^{95 98 116 117}

PALEO may assist with short-term reductions in fat mass while maintaining lean body mass; however, limited CHO intake can impair power, repeated-effort capacity, and hydration management, which are crucial in combat sports [,]. Its restrictive profile may also increase LEA and micronutrient deficiency risk if applied during weight-cut periods. Strategic CHO intake before, during, and/or immediately after training becomes essential when a PALEO diet is employed in weight-category sports. ^{82 83}

Evidence suggests that CP can enhance metabolic adaptations in endurance sports, such as an increased capacity to oxidize fats and preserve glycogen during prolonged effort []. These adaptations could delay fatigue during ultra-endurance events or prolonged tests (>2–3 h). ¹²

However, this does not always translate into direct improvements in competitive performance, especially in events that require maintaining intensities close to the anaerobic threshold, where CHO availability remains a determining factor []. Therefore, it is recommended to alternate "low" and "high" sessions according to the objective of the training cycle and the type of session. ¹³

In sports based on power and explosive strength, CHO are essential for maintaining the ability to perform repeated maximal effort. Although training with low CHO availability may induce certain metabolic adaptations, CHO reduction is not recommended in these disciplines, as it could compromise the quality of the session and strength gains []. ⁹⁵

In team sports (soccer, basketball, and hockey), the ability to perform repeated sprints and maintain intensity is highly dependent on muscle glycogen. CP may be used during preparatory phases to improve aerobic capacity and fat oxidation, during competitive and high-load phases, and maintaining a high CHO intake is a priority to sustain performance []. ¹

Sprint athletes require frequent high-CHO availability to sustain maximal neuromuscular output. Periodized "train-low" sessions may enhance metabolic signaling but should be minimized in sprinters, because low-CHO training reduces power, technique quality, and session intensity [,]. CP can be applied selectively, but "compete high" and "sprint-session high" are essential principles for this group. ^{9 119}

Aesthetic athletes benefit from CP because it allows technical training to occur with adequate CHO availability while enabling tighter energy control during lighter sessions. This approach helps reduce LEA risk and supports technical skill acquisition, concentration, and hormonal balance during demanding practices [,,]. Strategic high-CHO days before choreography or apparatus sessions improve precision and may reduce injury risk. ^{98 116 117}

CP is particularly useful in weight-category sports because it allows controlled CHO reduction during early preparatory phases while preserving glycogen availability before sparring simulations and competition [,,]. Alternating low- and high-CHO days helps regulate body mass without compromising strength and speed. Reintroduction of high-CHO availability before weigh-ins and competition is essential for optimal performance. ^{9 18 27}