Interactions between exercise, environmental factors, and diet in modulating appetite-regulating hormones: implications for athletes and physically active individuals
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Exercise, environmental conditions, and diet are integral to athletes’ health and performance. Understanding how these factors interact to influence appetite-regulating hormones is a growing area of interest in sports science. This knowledge facilitates the development of personalized strategies for precisely monitoring and improving dietary intake, enhancing well-being, and improving athletic performance. For this narrative review, databases like “PubMed,” “SportDiscus,” “Scopus,” “ProQuest,” and “Google Scholar” were referred to using Boolean operators (AND, OR) to combine keywords related to exercise, environmental conditions, diet, and appetite-regulating hormones. High-intensity interval training, sprint interval training, resistance exercises, and high-intensity aerobic exercises were found to enhance satiety and suppress appetite by increasing appetite-suppressing hormones while reducing ghrelin levels. Greater exercise intensity prolonged appetite suppression by sustaining elevated levels of satiety hormones. Environmental factors such as high altitude, hypoxia, and extreme heat were associated with increased satiety, reduced appetite, and lower energy intake. Conversely, exposure to cold temperatures and participation in cold water exercises stimulated appetite. Dietary interventions, particularly ketogenic and high-protein diets, promoted satiety by increasing glucagon-like peptide-1 levels and decreasing ghrelin levels. Calorie restriction, especially when meals were infrequent but included breakfast, helped maintain satiety for extended periods by elevating satiety hormones. Integrating personalized exercise routines with dietary strategies while considering environmental adaptations is essential for optimizing appetite regulation, athletic performance, and overall health.
Appetite is regulated both centrally, through neural signals in the hypothalamus, and peripherally, via hormonal mechanisms. Several key hormones play essential roles in appetite regulation, such as ghrelin, leptin, peptide YY or peptide tyrosine-tyrosine or pancreatic peptide YY (PYY), pancreatic polypeptide (PP), glucagon-like peptide 1(GLP-1), cortisol, insulin, and cholecystokinin (CCK) [1]. Among these, ghrelin and leptin are the two primary hormones involved in appetite regulation [2]. Ghrelin, commonly referred to as the hunger hormone, is secreted by the stomach and acts as a potent appetite stimulant. Ghrelin also inhibits insulin secretion and helps maintain glucose homeostasis during starvation. Additionally, ghrelin regulates energy homeostasis by decreasing thermogenesis, which reduces energy expenditure while simultaneously stimulating appetite to ensure sufficient energy intake to meet the energy demands of the body [3].
Leptin, known as the satiety hormone, is secreted by the adipose tissue and serves as the primary appetite-suppressing hormone, which stimulates the secretion of other appetite-suppressing hormones such as GLP-1 and PYY [2,4]. Elevated leptin levels prolong the sensation of satiety more effectively compared to other appetite-suppressing or satiety-inducing hormones [1]. Another key hormone involved in appetite control is CCK, which is secreted by the intestines and plays a crucial role in fat and protein digestion. CCK stimulates the release of pancreatic and gastric juices and delays gastric emptying, allowing for more efficient digestion. Additionally, early phase satiety was stimulated, promotes GLP-1 and PYY secretion, and simultaneously inhibits ghrelin, contributing to appetite suppression after food intake [1,5]. GLP-1, a peptide hormone produced in the intestine, signals satiety and suppresses appetite. Stimulation of insulin release following food intake contributes to postprandial glucose regulation. Due to its role in appetite suppression and glucose control, GLP-1 remains highly effective in the treatment of type II diabetes mellitus and obesity [6]. PYY, secreted into the intestine during macronutrient digestion, plays a crucial role in delaying gastric emptying and suppressing appetite, facilitating proper digestion [1]. PYY regulates body weight by reducing food intake and increasing energy expenditure. Elevated PYY levels persist for several hours, typically peaking 1 to 2 hours postprandially. The calorie load and nutrient composition of food significantly influence PYY elevation and peak levels [7]. Insulin, produced by pancreatic beta cells, plays an important role in appetite inhibition. As glucose is absorbed into cells after food intake, insulin signals the brain that sufficient energy is available, leading to appetite suppression. Additionally, insulin interacts with the brain and liver to reduce food intake and promote the release of other appetite-suppressing hormones [8].
The adrenal glands release cortisol, commonly referred to as a stress hormone, in response to stress (mental, physical, or metabolic), hunger, or hypoglycemia caused by insulin resistance. Elevated cortisol levels trigger cravings for high-calorie foods and stimulate the release of ghrelin, which enhances hunger and cravings, particularly for fried, processed, and sweet foods. Consumption of calorie-dense foods stimulates the release of dopamine, a neurotransmitter linked to reward and happiness, which alleviates stress and lowers cortisol levels. By promoting cravings for energy-dense foods, cortisol plays a vital role in appetite regulation and immediate energy availability [9].
Scope of the Study
This narrative review aims to elucidate the complex relationship between exercise, environmental factors, diet, and appetite-regulating hormones in athletes. Understanding the interactions between these factors and their impact on appetite hormones presents a novel approach in sports science, with the potential to develop personalized strategies for effectively monitoring and improving diet, well-being, and performance in athletes. This review integrates these three complex fields to explore their impact on appetite regulation. Although the focus is primarily on athletes, some studies on nonathletic populations have been included, as these participants underwent exercise trials, a key aspect of this study. Athletes typically have higher energy demands and more adaptive physiological responses, meaning that the effects observed in nonathletic individuals may provide valuable insights into the potentially greater impact on athletes. Including such studies provides a more comprehensive understanding of how exercise, environmental factors, and diet influence appetite-regulating hormones, particularly in athletic populations. This study serves as a foundation for future research, highlighting the need for long-term, diverse, and large sample investigations to enhance the applicability and effectiveness of these strategies in real-world contexts.
Methodology
This narrative review was conducted by searching relevant literature across multiple databases, including PubMed, SportDiscus, Scopus, ProQuest, and Google Scholar. The search strategy involved the use of Boolean operators (AND, OR) to combine keywords related to exercise (e.g., “high-intensity interval training,” “moderate-intensity continuous training,” “resistance exercise”), environment (e.g., “altitude,” “hypoxia,” “temperature”), diet (e.g., “calorie restriction,” “hydration,” “nutrient intake,” “meal timing”), and appetite-regulating hormones (e.g., “ghrelin,” “leptin,” “insulin,” “peptide YY,” “cholecystokinin,” “Glp-1”). Studies were selected based on their relevance to athletic and physically active populations, although research on nonathletes was included if insights into exercise-induced hormonal changes were provided. Only articles published in English were included.
Effect of Exercise on Appetite-Regulating Hormones
Exercise induces a temporary reduction in appetite, commonly referred to as “exercise-induced anorexia,” which contributes to a short-term negative energy balance [10]. Earlier studies suggested that ghrelin remained unaffected by acute exercise; however, recent findings indicate that acylated ghrelin, the biologically active form responsible for appetite stimulation, experiences transient suppression during running and resistance exercise (RES). Beyond ghrelin, research has increasingly focused on episodic gut hormones, particularly PYY, GLP-1, and PP, due to their appetite-suppressive effects. Aerobic exercise has been shown to increase plasma concentrations of these hormones in both lean and obese individuals [10]. These hormonal responses can remain elevated for an hour or longer post-exercise, contributing to exercise-induced appetite suppression [10]. Gender differences in these hormonal responses have also been observed, with women exhibiting a greater tendency for exercise-induced appetite stimulation than men. This variation may be attributed to the physiological necessity of maintaining adequate body fat to support reproductive function [10].
High and moderate-intensity exercise
High-intensity exercises, such as high-intensity interval training (HIIT), has been shown to increase appetite-inhibitory hormone levels, such as PYY, PP, and GLP-1, ultimately leading to a reduction in ghrelin concentrations and a subjective decrease in appetite and hunger, a physiological response associated with exercise-induced anorexia [11-14]. Ghrelin concentrations decrease after HIIT exercises [15], while GLP-1 responses appear more variable. In contrast, PYY concentrations elevate after high-intensity continuous training (HICT) and sprint interval training (SIT) [11]. Figure 1 illustrates the occurrence of exercise-induced anorexia during HIIT.
A positive relationship exists between exercise intensity and hormonal responses, with subjective appetite variations influenced by gender and training patterns. Appetite suppression, lower ghrelin levels, and increased PYY concentrations [16] are observed following both SIT and moderate-intensity continuous training (MICT) in both men and women [17]. However, women experience a significantly greater reduction in subjective appetite after both SIT and MICT [17] than men [11]. Beer et al. [18] in 2020 reported a more pronounced reduction in ghrelin levels and energy intake following SIT (170% peak oxygen consumption for 15 seconds, alternating with 32% peak oxygen consumption for 60 seconds) compared to MICT (60% peak oxygen consumption) in both men and women. These findings emphasize potential gender-based variability in appetite regulation, suggesting that hormonal responses to exercise intensity may differ between genders.
High-intensity intermittent exercise, HIIT, SIT, and MICT have been shown to increase GLP-1 levels and decrease ghrelin levels, leading to appetite suppression without altering energy intake [19,20]. HICT in cycling sessions prolongs appetite suppression compared to moderate-intensity continuous exercises, whereas both HICT and MICT result in similar reductions in energy intake [21]. This variation in hunger suppression between HICT and MICT is due to the secretion of the satiety hormone PYY, which is directly dependent on exercise intensity [21]. Given that HICT elicits a greater physiological demand than MICT, the secretion of PYY is enhanced to a greater extent. Consequently, exercise intensity exerts a significant influence on appetite hormone levels and subjective appetite. Additionally, gender, body composition, hydration status, and exposure to hypoxic environments serve as key factors modulating appetite regulation and hormonal responses [11]. Elite adolescent rugby players adjust their energy intake based on training type, regardless of energy expenditure during exercise [22]. This highlights the importance of providing energy and nutritional education to support optimal physical fitness and performance in young athletes.
Brisk walking
Despite net energy expenditure, a single brisk walking session does not elicit compensatory appetite responses or alter acylated ghrelin levels. This suggests that brisk walking may contribute to weight management without increasing hunger or energy intake [23]. Brisk walking in a fasted state does not significantly differ from walking in a fed state in terms of gastric emptying rate, as fat mobilization for metabolism increases. Additionally, low-intensity exercise in a fasted state does not trigger a compensatory increase in energy intake in the hours immediately following exercise. Therefore, fasted brisk walking may contribute to body mass maintenance without triggering excessive energy consumption [24]. Similarly, cycling (high-intensity; equal to or more than 70% of maximal oxygen uptake) promotes appetite suppression by increasing PYY and reducing ghrelin levels in men [25]. Furthermore, physically active individuals exhibit stronger post-breakfast satiety, as elevated PYY enhances appetite suppression sensitivity in women, regardless of activity level [26,27].
Aerobic exercise
Aerobic exercise is widely recommended for weight management; however, its effects on ghrelin and leptin levels remain inconsistent, particularly in studies involving athletes. Regular low-intensity aerobic exercise has been associated with decreased leptin levels and potentially increased ghrelin levels in healthy females [28]. Two consecutive days of aerobic exercise do not stimulate appetite or lead to significant alterations in appetite hormones, except for a transient increase in PYY and a decrease in insulin levels. Therefore, short-term exercise does not trigger compensatory changes in appetite regulation or food intake [29]. While short-term aerobic exercise increases PP levels, no significant changes are observed in PYY concentrations or appetite sensations [30].
High-intensity aerobic exercise lasting up to 45 minutes does not reduce subjective appetite or absolute food intake in trained male endurance athletes. This suggests that endurance athletes may experience distinct physiological responses to exercise-induced appetite suppression, as well as variations in appetite perception and post-exercise hormonal signaling [31]. Aerobic exercise, particularly when performed at 60% oxygen uptake reserve (VO2R), may effectively reduce appetite-regulating hormones responsible for hunger signaling, such as acylated ghrelin and its biological catalyst, ghrelin O-acyltransferase (GOAT) [32-34]. Additionally, aerobic exercise promotes increased satiety-inducing hormone levels, including PP, PYY, and GLP-1 [35], in both normal-weight and obese individuals. Therefore, aerobic exercise represents a non-pharmacologic approach to appetite regulation and may contribute to the treatment and management of obesity [32-34].
Resistance exercise
Ghrelin concentration declines following RES, delaying meal timing but not leading to reduced energy intake [36]. Resistance and aerobic exercise suppress appetite-regulatory hormones, with RES having a greater effect on ghrelin suppression and aerobic exercise increasing PYY and GLP-1 levels. However, neither exercise modality leads to increased energy intake, indicating that energy expenditure during exercise is not compensated for through increased hunger or food intake [32,37]. A study on physically active men demonstrated that moderate- and low-load RESs suppress hunger by reducing ghrelin concentrations and increasing PYY levels [38]. Similar findings were reported in women, where RES led to reduced hunger, decreased ghrelin levels, and increased PYY and satiety levels [39]. Ataeinosrat et al. [40] in 2022 found that circuit resistance training (CRT) and interval resistance training (IRT) exerted a greater effect on GLP-1 elevation compared to traditional resistance training (TRT) in obese men. These results suggest that training intensity plays an important role in hormonal appetite regulation, as CRT and IRT involve shorter rest periods and higher training intensities than those of TRT, leading to greater energy expenditure and metabolic stress, which may enhance GLP-1 secretion. Table 1 presents the effects of various exercise modalities on appetite-regulating hormone levels [10-21,23-34,36,37,41].
Effect of Environmental Factors on Appetite-Regulating Hormones
Exercising under different environmental conditions affects not only physical performance but also appetite hormones and post-exercise energy intake. Environmental factors, such as temperature, altitude, and oxygen levels, play an important role in energy homeostasis and appetite regulation.
Hypoxic conditions
Research on the effects of exercise under hypoxia conditions on appetite suppression has yielded mixed results. Some studies indicate that intense exercise, irrespective of oxygen availability, exerts appetite-suppressive effects [42]. These findings are consistent with previous research in highly trained endurance women, demonstrating that an acute bout of endurance exercise, high-intensity exercise (HIE), or moderate-intensity exercise can suppress appetite-regulating hormones, such as ghrelin, reduce subjective hunger, and increase PYY and GLP-1 levels [41]. HIIT has also been shown to reduce plasma acylated ghrelin concentrations, thereby suppressing appetite and lowering energy intake under both hypoxic and normoxic conditions [11]. Notably, while exercise intensity appears to be a stronger determinant of appetite suppression than oxygen availability, hypoxia plays a significant role in modulating appetite regulation. Several studies indicate that hypoxia suppresses appetite and hunger by reducing energy intake while increasing PYY and satiety levels [10,43,44]. Therefore, exercising under hypoxia conditions may effectively prolong appetite suppression and reduce energy intake, potentially contributing to weight loss [44]. However, the effects of hypoxia on appetite regulation should not be viewed in isolation, as altitude, temperature, metabolic adaptations, and exercise intensity also play crucial roles in modulating appetite and energy balance [10].
High altitude
Living high-training low approach induces efficient weight loss and leads to increased GLP-1 levels, potentially mediated by Interleukin-6 (IL-6). This approach may serve as an effective method for weight loss and appetite regulation in adolescents with obesity [45]. The early phase physiological stress response associated with high-altitude training may lead to a reduction in acylated ghrelin levels in male power-trained athletes during intense training camps. However, this decline in ghrelin levels may be associated with stress-induced hormonal changes rather than direct appetite suppression [46].
Following exercise at an altitude of 4,300 m (a severely hypoxic environment with lower oxygen availability), significantly lower levels of acylated ghrelin, PP, and composite appetite scores were observed compared to those recorded at sea level and 2,150 m. Additionally, energy intake was lower at 4,300 m than that at lower altitudes. Exposure to high altitudes (>4,000 m) induces high-altitude anorexia, characterized by appetite suppression and reduced post-exercise energy intake. This response is associated with decreased ghrelin levels [47,48] and elevated leptin, insulin, and CCK levels [49]. However, this effect is not observed at moderate altitudes [47]. Figure 2 illustrates the effects of various environmental factors on appetite regulation.
High and low temperature
Exercise training in a hot environment at high altitudes enhanced satiety, primarily due to increased plasma PYY concentrations [50]. Hypoxic (high altitude) and hot environments contribute to reduced food intake, potentially due to their anorexic effects [10]. Short-term exposure to hypoxia and normobaric hypoxia can suppress appetite and reduce ghrelin levels [43], even in the absence of cold temperatures [44,51,52]. This response is accompanied by increased PYY levels and decreased energy intake [43,44]. Conversely, exercising in extremely low temperatures and cold weather leads to a significant increase in energy expenditure, which subsequently stimulates energy intake [50,53,54]. For athletes aiming to lose weight, vigorous exercise is likely to transiently suppress appetite without necessarily resulting in overeating [10]. Appetite suppression is observed more frequently in hot temperatures than in cold environments. PYY levels remain elevated, while GLP-1 concentrations remain unchanged at both temperatures. Leptin levels increase in hot environments but decline in cold environments, whereas ghrelin levels decrease in hot environments and increase in cold environments [55].
A reduction in energy intake after exercise in hot conditions is associated with elevated tympanic temperature and higher PYY concentrations, a hormone linked to satiety signaling [50,56]. Exercising in warmer environments may be preferable for achieving a short-term negative energy balance; however, precautionary measures should be taken to prevent excessive heat exposure, dehydration, and heat-related illnesses [56]. However, appetite suppression in hot environments can support calorie deficit and weight loss. This may also lead to weakness, hypoglycemia, and dehydration. This effect could pose health risks for individuals, particularly athletes and military personnel, who must consume adequate energy to meet physiological demands and sustain performance [57].
Water immersion
Post-exercise water immersion, whether in cold or neutral temperatures, increased short-term energy intake in trained men compared to no immersion. These findings have important implications for athletes who use water immersion as a recovery method after exercise [58]. Exercising in cold water is particularly associated with an increased food intake [10,59,60]. Conversely, Ptaszek et al. [61] in 2023 reported an increase in leptin levels following 4 minutes of cold-water swimming in both men and women. Zeyl et al. [62] in 2004 demonstrated that acute and repeated cold water immersion produce different hormonal responses. While acute cold water immersion leads to a significant decline in leptin levels, repeated exposure results in increased leptin levels.
Cryotherapy
Post-exercise whole-body cryotherapy at ‒140 °C for 3 minutes increases energy intake during the subsequent meal in well-trained male athletes. Interestingly, this increase in energy intake was not linked to changes in appetite-regulating hormone levels. Instead, activation of the parasympathetic nervous system and enhanced gastric motility may be responsible for this effect. Therefore, whole-body cryotherapy may serve as a valuable recovery technique to improve athletic performance [63]. Similarly, Lushchyk et al. [64] in 2019 observed a reduction in leptin levels following whole-body cryotherapy, indicating increased appetite and energy intake. However, another study reported gender-based differences, showing that leptin levels increased in women but decreased in men following a 3-minute whole-body cryotherapy session [61]. Table 2 presents the effects of various environmental factors on appetite-regulating hormone levels [10,11,42-64].
Effect of Dietary Factors on Appetite-Regulating Hormones
Appetite regulation involves a complex relationship between gut hormones and the physiological sensations of hunger and satiety. Leptin, CCK, PYY, GLP-1, and PP act as appetite-suppressing (anorexigenic) hormones, whereas ghrelin functions as an appetite-stimulating (orexigenic) hormone. Disruptions in hormonal homeostasis can lead to appetite dysregulation, energy deficiencies, eating disorders, and weight gain, all of which may negatively impact overall health and athletic performance.
Macronutrient composition and specific dietary components
Low-carbohydrate and high-fat intake
A ketogenic diet increases GLP-1 levels while suppressing ghrelin secretion compared to a high-carbohydrate diet or a standard diet in highly trained cyclists and triathletes. Additionally, a higher fat-free mass is associated with lower ghrelin levels, suggesting that maintaining or increasing fat-free mass may serve as a beneficial strategy for appetite regulation. Very low-carbohydrate, high-fat diets have demonstrated anorexigenic effects on objective appetite measures [65].
Exercise, regardless of dietary fatty acid composition, reduces leptin and insulin levels while increasing PYY levels over 24 hours. However, dietary fatty acid composition does not appear to exert a significant impact on hunger or satiety markers [66]. Conversely, another study reported that aerobic exercise following a low-fat diet led to higher ghrelin levels and lower leptin levels compared to exercise after consuming a high-fat diet in highly trained male endurance athletes [67].
Protein intake
A diet with a higher protein-to-carbohydrate ratio appears to be advantageous for athletic performance by maintaining body weight and reducing appetite. This effect is particularly attributed to lower concentrations of GLP-1, gastric inhibitory polypeptide (GIP), leptin, and ghrelin in athletes, which may also help reduce the risk of hypoglycemia [68]. Increasing whey protein supplementation beyond 20 g does not appear to further enhance satiety or decrease food intake in male athletes. Consequently, athletes can incorporate additional whey protein into their diet without significantly affecting appetite or subsequent food intake, potentially helping in meeting protein requirements without displacing other essential nutrients [69].
Bio-functional foods and nutrients
Consuming a riceberry rice diet before exercise enhances the production of total GLP-1, leading to greater fullness perception and reduced hunger compared to white rice. Additionally, riceberry rice may contribute to limiting muscle damage, as evidenced by lower creatine kinase concentrations. Incorporating riceberry rice into pre-exercise nutrition helps regulate appetite hormones while also mitigating muscle-related discomfort [70].
The inclusion of bio-functional ingredients, such as vitamin D3, n-3 fatty acids, and probiotics, influences subjective appetite ratings in a varied manner. Increased hunger was reported following fruit juice consumption containing a combination of biofunctional ingredients, vitamin D3, and probiotics [71]. An increase in thirst was observed when fruit juice was supplemented with bio-functional combinations of n-3 fatty acids and probiotics [71]. In contrast, fruit juices containing n-3 fatty acids alone or in combination with other bio-functional ingredients resulted in a lower preoccupation with food [71]. Enriching fruit juice with n-3 fatty acids, vitamin D3, or probiotics can improve postprandial glycemic responses, potentially contributing to improved glycemic control [71]. Eight weeks of HIIT combined with vitamin D supplementation resulted in lower insulin levels, reduced hunger, decreased total calorie intake, and appetite suppression while simultaneously increasing satiety and fullness through increased PYY levels. However, no significant changes in ghrelin levels were observed [12].
Dietary patterns and meal timing
Pre- and post-exercise nutrition
During resistance training, a short-term suppression of appetite occurs, regardless of exercise intensity. Notably, the consumption of low-fiber carbohydrates and protein-rich foods or beverages 30–60 minutes before training was associated with better appetite suppression. Pre-workout meals or snacks with these characteristics contribute to improved appetite control during exercise. The extent of appetite suppression depends on training intensity, with higher-intensity exercise leading to more significant and prolonged suppression. Both men and women experience this appetite-reducing effect, though the response appears to be slightly pronounced in women [72]. However, noting that appetite regulation in women may be affected by hormonal fluctuations throughout the menstrual cycle is important. Therefore, the timing and macronutrient composition of pre-exercise nutrition plays a crucial role in appetite regulation during resistance training sessions. Consuming a balanced meal 2–4 hours before training or a small, easily digestible snack 30–60 minutes before training helps stabilize appetite and provide energy for exercise [72]. Hunger and ghrelin levels increase, while satiety and leptin levels decline more significantly after aerobic exercise following a low-fat diet compared to a high-fat diet in highly trained male endurance athletes [67]. Post-exercise dairy-based recovery beverages may reduce energy intake immediately after a meal, offering potential benefits for weight management. However, these beverages do not significantly affect appetite-related responses when compared to carbohydrate-based beverages [73].
Meal frequency and timing
Morning-loaded diets play a significant role in maintaining calorie deficits and achieving weight loss. Satiety hormones (GLP-1, PYY, and GIP) increase significantly, whereas the hunger hormone ghrelin decreases after a morning-loaded diet [74]. These hormonal changes persist for a longer duration compared to an evening-loaded diet. As a result, morning-loaded diets slow gastric emptying and provide prolonged appetite suppression in contrast to evening-loaded diets. Additionally, reduced hunger, lower energy intake, and improved eating behavior were observed throughout the day following morning-loaded diets [74]. Similarly, consuming low-frequency meals (eating only two major meals per day, including breakfast) was associated with reduced fasting leptin and GIP levels and increased fasting PP and ghrelin levels. However, low-frequency meal patterns increase satiety and suppress appetite more effectively by reducing hunger and postprandial ghrelin levels for a longer duration than consuming multiple frequent meals (six small meals per day) [75].
Calorie restriction
Gut hormones play a crucial role in eating behavior, alongside cultural and socioeconomic determinants [76]. Both calorie restriction and time-restricted feeding lead to increased hunger and ghrelin levels while simultaneously reducing satiety, leptin, insulin, and GLP-1 levels [76]. Although the balance between hunger and satiety shifts toward hunger following caloric restriction, time-restricted feeding appears to cause a less pronounced increase in hunger. Notably, elevated ghrelin levels occur more frequently during calorie restriction compared to time-restricted feeding [76]. Intermittent energy restriction (IER) impacts appetite-regulating hormones differently than continuous energy restriction (CER). Research indicates that IER is associated with reduced hunger, a lower desire to eat, increased satisfaction, and elevated PYY levels, suggesting a potential appetite-regulating and satiety-inducing advantage over CER [77]. However, additional factors may also influence appetite and dietary behavior among athletes. Therefore, appetite-regulating hormone responses should not be considered the primary determinants of potential variations in hunger and satiety during energy restriction [77].
A 12-week calorie restriction program combined with exercise resulted in reduced ghrelin levels and increased GLP-1 and PYY levels. Implementing this lifestyle can enhance satiety and prolong appetite suppression. While short-term results may not always be desirable, adopting a calorie deficit with an exercise routine may support sustainable weight and appetite management over the long-term [78]. However, excessive calorie restriction in combination with exercise training may have negative consequences, as stated by Isola et al. [79] in 2023. Dieting, reduced energy intake, and increased exercise lead to reductions in weight, fat mass, lean mass, energy intake, and leptin levels, alongside an increase in ghrelin levels, all of which contribute to adaptive thermogenesis in female and male athletes during competition preparation. However, these responses are temporary, as they tend to return to baseline during the recovery phase. Repeated exposure to such extreme dietary patterns may cause weight fluctuations and lead to the development of chronic disorders. Therefore, calorie restriction techniques to optimize appetite regulation should be implemented with caution under the supervision of nutritionists and coaches. Figure 3 illustrates the effects of calorie restriction and morning breakfast consumption on appetite.
Hydration status
Acute body water deficits do not substantially influence insulin and ghrelin levels, although they elevate glucagon levels. Its influence on glycemic regulation may be associated with individual water intake habits and basal copeptin/arginine vasopressin levels. Acute body water losses are associated with increased cortisol levels, particularly when combined with exercise or heat exposure. However, the independent effect of hypohydration on cortisol levels remains unclear due to various contributing factors, such as exercise intensity [80]. Alterations in hydration status are also linked to changes in subjective perceptions of hunger and specific food cravings [81]. The effects of various dietary factors on appetite hormone levels are shown in Table 3 [12,65,68-71,73-80].
Research Gaps and Limitations
Despite the comprehensive insights provided, this review identified several research gaps and limitations. Most studies have focused on short-term effects, leaving long-term impacts underexplored. A lack of research exists on the interplay between these factors in diverse athletic populations, including differences in age groups, genders, and sports disciplines. Experimental studies in this area remain limited, often characterized by small sample sizes. Furthermore, the combined impact of exercise, environment, and dietary factors on appetite hormones has not been comprehensively studied in previous research. Additionally, the majority of the existing research was conducted in controlled laboratory settings with small sample sizes, which may not reliably replicate the real-world conditions faced by athletes. Future studies should address these gaps by incorporating long-term, diverse, and ecologically valid research designs with larger sample sizes. Such studies would enhance the applicability of the findings and help develop more effective and individualized strategies for managing appetite and optimizing athletic performance.
Conclusion
The interplay between exercise training, environmental factors, and diet significantly influences appetite-regulating hormones, with important implications for appetite control in athletes and active individuals. This narrative review integrates these three complex fields to explore their collective effects on appetite and appetite hormones. Exercises such as HIIT, SIT, RESs, high-intensity aerobic exercises, and cycling increase levels of satiety hormones such as CCK, GLP-1, PYY, PP, and leptin while decreasing levels of the hunger hormone ghrelin. Therefore, these exercises play a role in inducing satiety and appetite suppression. The intensity of appetite suppression is directly linked to exercise intensity, with higher exercise intensity leading to longer-lasting appetite suppression through elevated PYY and GLP-1 levels and reduced ghrelin levels.
Environmental factors further modulate these hormonal responses, either amplifying or counteracting exercise-induced effects. Interestingly, the appetite-suppressing effects of HIE appear to be enhanced in extreme environments, such as high altitude and heat, suggesting a synergistic interaction between physiological stressors in regulating hunger and energy intake. Exercise in environmental conditions such as high altitude, hypoxia, and extremely hot temperatures modulates hormonal responses, suppresses hunger and appetite, maintains satiety, and reduces energy intake.
Dietary interventions are also critical modulators of appetite. Diets rich in proteins and complex carbohydrates can enhance satiety and effectively manage hunger. Ketogenic diets, characterized by high-fat and low-carbohydrate intake, promote appetite suppression by increasing GLP-1 levels, decreasing ghrelin levels, promoting satiety, and reducing hunger. Energy restriction is also an effective technique for improving the appetite suppression rate and satiety. When combined with exercise, energy restriction helps elevate appetite-suppressing hormones such as GLP-1, PPY, and PP while reducing ghrelin levels for extended durations. Additionally, time-dependent eating strategies, such as morning-loading diets and consuming two meals per day (including breakfast), have been proven effective in suppressing appetite for longer periods and reducing energy intake throughout the day, providing a strategic approach for athletes to optimize energy balance.
Combining these dietary approaches with HIE, high temperatures, hypoxia, and high altitudes can significantly enhance appetite suppression and satiety, thereby aiding in calorie management and weight control. The synergistic effect of diet, exercise intensity, and environmental stressors amplifies the release of satiety hormones, such as GLP-1 and PYY, while suppressing ghrelin, prolonging hunger suppression, and reducing overall energy intake. Conversely, cold environments with low temperatures and exercise in cold water stimulate appetite and increase energy intake by increasing ghrelin levels and decreasing GLP-1, PPY, and PP levels. Therefore, exercising in cold environments or engaging in cold water immersion with adequate oxygen levels can serve as a strategic approach to increasing calorie intake and supporting weight gain. This suggests a complex interaction between physiological stressors and appetite regulation, in which environmental factors may either reinforce or counteract exercise-induced changes in appetite hormone levels. This integrative perspective and the interconnected nature of these three factors underscore the importance of aligning dietary patterns with exercise and environmental conditions to achieve specific appetite and weight management goals in athletes and physically active individuals.
The findings of this review offer valuable insights for athletes, coaches, and nutritionists in developing evidence-based, effective, personalized strategies that integrate exercise modalities, environmental adaptation, and dietary interventions to enhance appetite regulation, performance, and overall health, ultimately achieving optimal body composition in athletes and physically active individuals. The combination of these factors has opened a new area of research. However, only a few studies have explored the combined effects of these factors. Given the potential synergistic influence of exercise intensity, environmental stressors, and dietary factors on appetite hormones, future studies should explore the integrated effects of exercise intensity in athletic populations. The emerging field of appetite regulation in sports science requires further investigation to develop impactful multifactorial strategies that enhance physiological adaptation and performance outcomes.
Article Information
Conflict of interest
No potential conflict of interest relevant to this article was reported.
Funding
None.
Data availability
Not applicable.
Author contribution
Conceptualization: ET, KK. Data curation: ET, KK. Formal analysis: ET, KK. Methodology: ET, KK. Writing–original draft: ET. Writing–review & editing: KK. Final approval of the manuscript: all authors.
Figure. 1.
Exercise-induced anorexia during HIIT. HIIT, high-intensity interval training; PYY, peptide YY or peptide tyrosine-tyrosine or pancreatic peptide YY; PP, pancreatic polypeptide; GLP-1, glucagon-like peptide 1.
Figure. 2.
Effect of environmental factors on appetite. PYY, peptide YY or peptide tyrosine-tyrosine or pancreatic peptide YY.
Figure. 3.
Effect of calorie restriction and morning-loaded breakfast on appetite. PYY, peptide YY or peptide tyrosine-tyrosine or pancreatic peptide YY; GLP-1, glucagon-like peptide 1; GIP, gastric inhibitory peptide.
Table 1.
Effect of exercise types on appetite-regulating hormones
GLP-1, glucagon-like peptide 1; GIP, gastric inhibitory peptide; HIIT, high-intensity interval training; PYY, peptide YY or peptide tyrosine-tyrosine or pancreatic peptide YY; PP, pancreatic polypeptide; NS, not specified; IER, intermittent energy restriction; CER, continuous energy restriction.
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Interactions between exercise, environmental factors, and diet in modulating appetite-regulating hormones: implications for athletes and physically active individuals
Figure. 1. Exercise-induced anorexia during HIIT. HIIT, high-intensity interval training; PYY, peptide YY or peptide tyrosine-tyrosine or pancreatic peptide YY; PP, pancreatic polypeptide; GLP-1, glucagon-like peptide 1.
Figure. 2. Effect of environmental factors on appetite. PYY, peptide YY or peptide tyrosine-tyrosine or pancreatic peptide YY.
Figure. 3. Effect of calorie restriction and morning-loaded breakfast on appetite. PYY, peptide YY or peptide tyrosine-tyrosine or pancreatic peptide YY; GLP-1, glucagon-like peptide 1; GIP, gastric inhibitory peptide.
Figure. 1.
Figure. 2.
Figure. 3.
Interactions between exercise, environmental factors, and diet in modulating appetite-regulating hormones: implications for athletes and physically active individuals
