Effects of Different Exercises Combined with Different Dietary Interventions on Body Composition: A Systematic Review and Network Meta-Analysis

With societal advancements and improvements in living standards, certain lifestyle habits that predispose individuals to various chronic diseases have become prevalent. Prolonged sedentary behavior, habitual sleep deprivation, and excessive eating contribute to metabolic disorders, which can lead to obesity or other chronic conditions. Regular physical activity is a well-established method to mitigate these health issues. The myriad benefits of exercise, including muscle mass maintenance, fat reduction, and enhanced metabolic function, are widely recognized. Historically, exercise has been the predominant strategy for weight management and health maintenance. However, in recent years, dietary interventions have gained prominence, offering alternative or complementary approaches to weight management. Notably, the most common dietary strategies include calorie restriction, 5/2 intermittent fasting, time-restricted eating, and the ketogenic diet. Extensive research supports the efficacy of these methods in both animal and human studies, demonstrating significant weight loss and metabolic advantages [1,2,3]. Recent studies have demonstrated that three dietary intervention strategies effectively lower both diastolic and systolic blood pressure [4,5,6,7,8], enhance mitochondrial function [9,10,11], reduce oxidative stress [4,5,12,13], improve insulin sensitivity [14,15,16,17], and foster beneficial modifications in the gut microbiome [18,19,20,21]. Specifically, calorie restriction, with a reduction in energy intake of approximately 15–30%, has been substantiated to decrease body weight, diminish body fat content, prolong lifespan, and lessen the incidence of age-related diseases, including cancer [22,23,24]. Furthermore, moderate calorie restriction (11.9 ± 0.7%) has been shown to significantly enhance quality of life, metabolic health, liver function, skeletal muscle mass, and immune capacity within a two-year period [25,26,27,28,29]. Unlike calorie restriction, intermittent fasting offers flexibility in food selection, integrating seamlessly with existing dietary regimes and presenting a viable, low-maintenance approach to health improvement [30]. Short-term results indicate that 5/2 intermittent fasting and time-restricted eating can achieve a weight reduction of 3–8% [31]. Intermittent fasting shows more pronounced effects in obese and overweight individuals, with an average weekly weight loss of approximately 0.2–0.5 kg [32], whereas individuals of normal weight may experience a reduction of about 0.2 kg per week [33]. Notably, about 75% of weight loss attributable to calorie restriction or intermittent fasting comprises fat mass, with the remaining 25% being lean body mass [34,35,36,37]. The ketogenic diet induces a metabolic state known as ketosis, where ketone bodies, rather than glucose, serve as the primary energy substrate, lowering blood glucose levels and facilitating the use of ketones for energy [38,39]. Additionally, the ketogenic diet has been associated with enhanced immune function [40,41], improved neurological health, and potential efficacy in treating epilepsy and inhibiting tumor growth [42]. Despite these benefits, some dietary interventions may lead to muscle mass reduction, consequently decreasing the basal metabolic rate [7,32], a factor that could be intertwined with overall weight loss [43,44,45]. The reduction in skeletal muscle can lead to various issues, including a lowered basal metabolic rate, impaired enhancement of exercise capacity, and reduced caloric burn [46,47,48]. Research has demonstrated that both aerobic and resistance training are highly effective at preserving lean body mass during weight loss efforts [49]. Subsequently, an increasing number of individuals have explored the combination of exercise and dietary interventions to mitigate the drawbacks of single interventions and achieve synergistic benefits. Recent trials have demonstrated the feasibility of combining exercise with dietary interventions; participants have been able to perform moderate to high-intensity endurance or resistance training during fasting periods of 12 to 36 h without adverse effects after adapting to the fasting regimen [44,45,50,51,52]. Research has shown that exercise surpasses calorie restriction in promoting fatty acid oxidation, elevating high-density lipoprotein levels [3,31,52,53], and enhancing mitochondrial function, while calorie restriction is more effective in reducing body weight [54]. Specifically, calorie restriction reduces oxidative stress, whereas exercise induces oxidative stress in skeletal muscles. These findings suggest that the benefits of exercise and calorie restriction are distinct, indicating that their combination might circumvent the limitations of single interventions and provide greater overall benefits [55,56]. Additionally, studies have indicated that time-restricted eating alone can lead to a reduction in lean body mass. However, research involving individuals who regularly engage in exercise training has found that combining time-restricted eating with resistance training maintains or increases muscle mass while significantly reducing subcutaneous fat mass [44,45]. Several meta-analyses have corroborated that combining exercise and dietary interventions is more effective than either approach alone in improving body composition, glycemic markers, and lipid profiles [57,58,59,60,61,62].

Therefore, an increasing number of studies have focused on combining exercise with dietary interventions to explore whether this approach can yield more effective weight loss outcomes. However, the effects of combining exercise with various dietary interventions differ across studies, and there is currently no comprehensive literature comparing the effects of exercise combined with different dietary interventions. Consequently, this study aims to summarize the outcomes of combining exercise with different dietary interventions and perform a network meta-analysis to investigate the differences in their effects. The objective is to provide evidence-based recommendations for individuals seeking to combine exercise with dietary interventions.

Our network meta-analysis included 78 controlled trials to assess the effects of combining exercise with different dietary interventions on body composition. By summarizing the included studies, we ranked the effects of four dietary interventions—calorie restriction (CR), 5/2 intermittent fasting (5/2F), time-restricted feeding (TRF), and the ketogenic diet (KD)—combined with exercise (aerobic, resistance, and mixed exercise) on body composition. Our results indicate that, compared to the other three interventions, combining exercise with calorie restriction is the most effective for reducing weight, BMI, and body fat percentage. For men, combining exercise with calorie restriction is the best approach to maintain lean body mass, while for women, combining exercise with time-restricted feeding is the most effective method for maintaining lean body mass. For exercise types, we conducted a subgroup analysis, categorizing the studies into three groups: aerobic exercise, resistance training, and mixed exercise. The results of the subgroup analysis showed that the trends in the effects of these three types of exercise combined with different dietary interventions on weight, body fat percentage, and lean body mass were generally consistent. However, there were some minor differences. Specifically, for weight reduction, when resistance training was performed, the combination with intermittent fasting was more effective than with calorie restriction or the ketogenic diet (). Supplementary Tables S2–S8

Dietary and exercise interventions have a significant impact on overall health improvement. Numerous studies have shown that dietary interventions can improve the body's inflammatory state [64], lower blood pressure, reduce blood lipids, and even alleviate symptoms such as body pain [65]. It is not only the nutritional content that positively affects the body; the quantity and timing of intake can also produce remarkable effects. Consistent with previous research, our study's results indicate that any dietary intervention is more effective than exercise alone in reducing weight. Peven's study suggests that even when exercise exceeds the recommended amount in physical activity guidelines, it is not as effective as dietary interventions for weight loss [54], supporting the findings of this NMA. CR + EX is significantly more effective in weight reduction compared to other interventions. The primary reason for this might be that CR + EX clearly defines daily caloric intake, preventing increased caloric intake due to the additional consumption brought by exercise. Although some studies have shown that intermittent fasting does not lead to compensatory eating behaviors [66,67,68,69] and reduces total intake by approximately 25% compared to normal eating patterns [70], when intermittent fasting and the ketogenic diet are combined with exercise, the enhanced metabolism induced by exercise can cause significant fluctuations in intake during feeding periods. This might lead to higher intake than dietary interventions alone, indirectly explaining why the weight reduction effect of exercise is not prominent, possibly due to increased intake. When total caloric intake is restricted, the additional consumption brought by exercise is reflected in weight loss. Subsequently, we conducted a subgroup analysis based on the type of exercise. The results remained consistent with the overall analysis when aerobic and mixed exercises were performed. Only when resistance exercise was performed did TRF + EX prove to be more effective than CR + EX. This finding requires further direct comparative research for verification. For BMI, our study's results are largely consistent with those for weight. The BMI formula is weight divided by the square of height, so its trend is generally consistent with the trend in weight.

To explore the effects of combining exercise with dietary interventions in the body, it is important not only to focus on weight loss but also to consider changes in body composition, particularly fat reduction [71,72]. Our study shows that for reducing body fat percentage, CR + EX is the most effective, while the other three interventions have similar effects, with KD + EX being the least effective in reducing body fat percentage. The reason for this may be that CR + EX creates a caloric deficit, and exercise helps maintain muscle mass and basal metabolic rate, resulting in these caloric deficits being reflected in reduced fat mass. Eglseer's network meta-analysis also demonstrated that calorie restriction combined with exercise is the most effective in reducing fat mass [73]. The least effective intervention, KD + EX, might be due to the high fat intake, leading to fat accumulation in the body. Although some studies indicate that the ketogenic diet can promote glucose and fat metabolism [74] and significantly reduce total cholesterol, low-density lipoprotein, and triglycerides [75,76], other research in the literature suggests that the ketogenic diet does not lead to weight gain but can slightly increase fat mass and fat percentage [77]. In our study, when comparing exercise combined with other dietary interventions, KD + EX might be effective in reducing body fat percentage compared to a control group, but the other three interventions are more effective. Interestingly, our study found that for reducing body fat percentage, the effect of TRF + EX is worse than TRF alone, 5/2F + EX is worse than 5/2F alone, and KD + EX is worse than KD alone. There might be three reasons for this outcome. First, it could be because exercise promotes fat absorption and storage during dietary interventions. Since fat is the most efficient energy source, the body may accumulate more fat once an exercise routine is established compared to the dietary intervention alone. Second, changes in body weight might affect body fat percentage. If the reduction in body weight is greater than the reduction in fat mass, the body fat percentage might increase. Regardless, body fat percentage is an important indicator of health, and an increase generally signifies adverse events. Lastly, upon closely examining the articles involving changes in body fat percentage, we found that while the fat data showed good consistency, the direct comparison results between groups did not show significant differences. Therefore, the final results might have been influenced by indirect comparisons, leading to significant findings. This aspect needs further experimental validation.

Studies have shown that the loss of muscle mass and strength poses serious challenges to physical function and carries significant health risks, including increased disability, frailty, and mortality [78,79]. Therefore, maintaining lean body mass is critically important. The results of the four intervention methods on maintaining lean body mass showed significant inconsistency (p = 0.004). To address this inconsistency, we first changed the statistical model and used the Bayesian-model-based GeMTC software for verification, but we were unable to perform consistency checks. We then suspected that heterogeneity among the included studies might be a factor. Some studies indicate that the type of exercise and the gender of the subjects greatly influence lean body mass. Furrer et al. demonstrated that resistance training typically leads to a significant increase in muscle fiber size, while endurance training mainly induces mitochondrial biogenesis and metabolic remodeling, resulting in enhanced oxidative capacity without substantially affecting absolute muscle mass [80]. We then conducted subgroup analysis based on the type of exercise. We found that the aerobic exercise subgroup still showed significant inconsistency (p = 0.001), but the resistance training and mixed exercise subgroups showed good consistency (resistance training: p = 0.2355; mixed exercise: p = 0.9881). Consequently, we ranked the effects of dietary interventions combined with resistance or mixed exercise on lean body mass, concluding that CR + EX and TRF + EX are the most effective in maintaining lean body mass. Genton et al. indicated that physical activity could delay lean body mass loss in men but not in women [81], although some research suggests this might be due to the lower intensity of physical activity in women compared to men [82]. If gender significantly impacts lean body mass maintenance, studies with a large difference in the number of male and female participants could lead to significant inconsistency. Our NMA results showed good consistency in both subgroups (women: p = 0.1759; men: p = 0.2033). Ultimately, we chose to conduct subgroup analyses by gender to avoid significant inconsistency, and our results confirmed the impact of gender on lean body mass maintenance.

For men, the best way to maintain lean body mass is CR + EX. For women, the best way to maintain lean body mass is TRF + EX. For both men and women, the least effective method for maintaining lean body mass is KD + EX. Research indicates that the ketogenic diet can reduce glycogen storage in muscles [83,84]. In muscles, glycogen is not stored alone but is combined with water in a ratio of 1:3 [85]. The ketogenic diet, often high in saturated fats, may lack essential nutrients, particularly carbohydrates, dietary fiber, and micronutrients such as calcium, magnesium, potassium, and vitamins A, B, and B6 [86,87]. Without sufficient carbohydrates in the diet, glycogen accumulation decreases, ultimately leading to a reduction in absolute lean body mass [88]. There is evidence that in untrained individuals, the ketogenic diet may lead to slightly higher lean body mass loss compared to a normal diet [89,90,91]. A meta-analysis assessing the impact of exercise combined with the ketogenic diet on body composition found that the ketogenic diet group had significantly lower lean body mass compared to the non-ketogenic diet group [92]. Some studies suggest that the ketogenic diet increases AMPK activity, which can inhibit mTOR signaling, a key regulator of muscle mass increase [93]. Other research indicates that long-term ketogenic diets may promote inflammation and increase the risk of cellular aging [94]. Thus, our NMA concludes that exercise combined with the ketogenic diet is the least recommended among the four intervention methods.

The results of this NMA indicate that combining calorie restriction with exercise yields the best overall effects on weight reduction, body fat percentage reduction, and maintenance of lean body mass, making it the optimal choice for improving body composition. Following this is time-restricted eating combined with exercise, which has a slightly lesser impact on body composition compared to calorie restriction combined with exercise. Notably, time-restricted eating combined with exercise is the most effective method for maintaining lean body mass in women. Although combining exercise with a ketogenic diet is effective for weight reduction, it is less effective in reducing body fat percentage and maintaining lean body mass compared to other interventions, making it a less favorable choice.