Eating more carbohydrates during intense training on a restricted diet helps preserve muscle-building hormones, according to Gram Research analysis. A 2026 randomized controlled trial of 16 active adults found that consuming 4.0 grams of carbohydrates per kilogram of body weight daily partially prevented drops in IGF-1 and other key hormones compared to eating only 1.5 grams per kilogram daily during periods of very low calorie intake combined with exercise.
When athletes eat very little food while exercising hard, their bodies go into survival mode and shut down important hormones. A new study found that eating more carbohydrates during these tough training periods can help protect some of these hormones, especially one called IGF-1 that helps muscles grow. Researchers had 16 active people follow strict diets for 4 days while exercising daily. Those who ate more carbs maintained better muscle function and kept their hormone levels from dropping as much as those eating fewer carbs. This research suggests that carbohydrate timing matters when you’re pushing your body to its limits.
Key Statistics
A 2026 randomized controlled trial of 16 recreationally active adults found that higher carbohydrate intake (4.0 g/kg/day) partially prevented the drop in IGF-1, a muscle-building hormone, compared to lower carbohydrate intake (1.5 g/kg/day) during 4 days of severe calorie restriction combined with daily exercise.
According to research reviewed by Gram, eating more carbohydrates during intense training on a restricted diet helped maintain blood lactate concentrations during both submaximal and maximal exercise, indicating better preservation of muscle energy production capacity.
A 2026 study of 16 active participants showed that body weight decreased by approximately 1.3% over 4 days during low energy availability, regardless of carbohydrate intake level, demonstrating that total calorie restriction drives weight loss independent of carbohydrate availability.
Research from 2026 found that how the body uses different fuel sources (fat versus carbohydrates) during low energy availability was determined more by sex than by carbohydrate intake, suggesting biological differences between men and women in metabolic adaptation.
The Quick Take
- What they studied: Whether eating more carbohydrates can protect your body’s hormones when you’re eating very little food while exercising intensely.
- Who participated: 16 recreationally active adults (9 women and 7 men) in good health who exercised regularly but weren’t professional athletes.
- Key finding: Eating more carbs (4.0 grams per kilogram of body weight daily) partially prevented the drop in important hormones like IGF-1 and testosterone compared to eating fewer carbs (1.5 grams per kilogram daily) during periods of very low food intake.
- What it means for you: If you’re doing intense training on a restricted diet, prioritizing carbohydrate intake may help preserve muscle-building hormones and athletic performance. However, this was a short 4-day study, so long-term effects remain unclear.
The Research Details
This was a randomized crossover study, meaning each participant experienced both conditions in random order. For 4 days at a time, participants ate only 25 calories per kilogram of their muscle mass daily—a very restricted intake—while exercising to burn an additional 20 calories per kilogram. They did this twice: once eating low amounts of carbs (1.5 grams per kilogram daily) and once eating high amounts (4.0 grams per kilogram daily). Everything they ate was carefully measured and controlled by researchers. The researchers measured hormones, how their bodies used fuel, and athletic performance before, during, and after each 4-day period.
The crossover design is powerful because each person serves as their own comparison—researchers can see exactly how the same person responds to different carbohydrate amounts under identical conditions. This reduces confusion from individual differences. The strict control of food intake and exercise ensures that carbohydrate availability was the main variable being tested.
Understanding how carbohydrate intake affects hormones during intense training is important for athletes, fitness enthusiasts, and people doing extreme diets. Hormones like IGF-1, testosterone, and leptin control muscle growth, recovery, and metabolism. If carbs can protect these hormones during tough training periods, athletes could maintain better performance and muscle health. This research helps explain the mechanisms behind why some nutrition strategies work better than others during intense exercise.
This study has several strengths: it used a randomized crossover design (considered high-quality), carefully controlled all food intake, and measured multiple hormones and performance markers. However, it was short (only 4 days), involved a small number of people (16), and only included recreationally active individuals—not elite athletes. The findings may not apply to longer training periods or different populations. Some hormone changes were in the expected direction but didn’t reach statistical significance, meaning they could have occurred by chance.
What the Results Show
When participants ate very little food while exercising, their body weight dropped by about 1.3% over the 4 days, regardless of carbohydrate intake. However, eating more carbs did help preserve some important hormones. Insulin, leptin (which controls hunger), and testosterone all dropped less when people ate more carbs compared to fewer carbs, though these differences were not statistically significant.
The most important finding was that eating more carbs partially prevented the drop in IGF-1, a hormone crucial for muscle growth and recovery. This suggests that carbohydrate availability directly protects this muscle-building hormone during periods of low food intake. Additionally, high carbohydrate intake helped maintain blood lactate levels during both submaximal and maximal exercise, indicating that muscles could still produce energy efficiently.
Interestingly, how the body used different fuel sources (fat versus carbohydrates) was largely determined by sex rather than carbohydrate intake. Women and men showed different patterns of fuel usage, but eating more carbs didn’t change these patterns much. Maximum aerobic capacity (VO₂peak) and peak power output remained unchanged regardless of carbohydrate intake or the low-food condition.
The study found that low food availability shifted the body toward burning more fat at rest and during exercise, which is a normal survival adaptation. This shift happened regardless of how many carbs people ate. Sex differences were notable—men and women responded differently to the low-food condition in terms of which fuels their bodies preferred to burn. The preservation of blood lactate with higher carbohydrate intake suggests that muscles maintained better glycolytic function (the ability to produce quick energy), which is important for high-intensity exercise performance.
Previous research has shown that low energy availability causes predictable hormone changes and metabolic shifts. This study builds on that knowledge by isolating carbohydrate’s specific role. While earlier studies suggested carbohydrates might be protective, this is one of the first to carefully test whether carbohydrate availability specifically modulates the endocrine response to severe calorie restriction. The findings align with the concept that carbohydrate availability is distinct from total energy intake and has independent effects on performance and hormones.
This study lasted only 4 days, so we don’t know if these protective effects of carbs continue over weeks or months of training. The sample size was small (16 people), and all were recreationally active—results may differ for elite athletes, sedentary people, or those with certain health conditions. Some hormone changes were in the expected direction but didn’t reach statistical significance, meaning they might have occurred by chance. The study didn’t measure longer-term outcomes like muscle loss or recovery after the restriction period ended. Additionally, the very low calorie intake (25 kcal/kg FFM) is extreme and not typical of most training scenarios.
The Bottom Line
If you’re doing intense training while eating a restricted diet, prioritize carbohydrate intake—aim for the higher end of recommendations (around 4 grams per kilogram of body weight daily rather than 1.5 grams). This appears to help preserve muscle-building hormones and maintain exercise performance. However, avoid prolonged periods of very low calorie intake combined with intense exercise, as this can harm your health. Moderate confidence in this recommendation based on a small, short-term study.
Athletes preparing for competition, people doing intense training programs, and fitness enthusiasts managing their diet should pay attention to this research. It’s particularly relevant for those doing periodized training where they intentionally reduce calories. This research is less relevant for people doing moderate exercise, those eating adequate calories, or anyone with a history of eating disorders. Consult a sports nutritionist or doctor before making major diet changes, especially if combining calorie restriction with intense exercise.
The protective effects of higher carbohydrate intake appeared within the 4-day study period, suggesting relatively quick benefits. However, we don’t know how long these benefits last or whether they continue over weeks of training. You might notice improved exercise performance and recovery within days of increasing carbohydrate intake during intense training, but longer-term effects on muscle growth require weeks to months to assess.
Frequently Asked Questions
Does eating more carbs help preserve muscle during intense training on a diet?
Yes, partially. A 2026 study found that eating 4.0 grams of carbs per kilogram of body weight daily preserved muscle-building hormones like IGF-1 better than eating only 1.5 grams per kilogram during intense training with restricted calories. However, this was tested over only 4 days.
How many carbs should I eat if I’m doing intense exercise while dieting?
Based on this research, aim for 3.5-4.0 grams of carbohydrates per kilogram of body weight daily during intense training periods. This level better protected hormones and exercise performance compared to 1.5 grams per kilogram in the study.
Can carbs prevent hormone drops when eating very little food?
Carbohydrates can partially prevent hormone drops, but not completely. The 2026 study showed that higher carb intake reduced—but didn’t eliminate—decreases in insulin, leptin, and testosterone during severe calorie restriction combined with exercise.
Does carbohydrate intake affect how my body burns fat during training?
Not significantly, according to this research. The study found that how much fat versus carbohydrates your body burns during low energy availability is determined more by whether you’re male or female than by how many carbs you eat.
How long does it take to see benefits from eating more carbs during training?
This study showed benefits within 4 days, suggesting relatively quick effects on hormone preservation and exercise performance. However, longer-term effects over weeks or months of training remain unknown from this research.
Want to Apply This Research?
- Log daily carbohydrate intake in grams per kilogram of body weight, and track one performance metric (like max power output or lactate threshold test results) weekly to see if higher carb intake improves your results during intense training phases.
- During weeks when you’re doing intense training, set a daily carbohydrate target of 3.5-4.0 grams per kilogram of body weight and log it in your nutrition app. Compare your energy levels, workout performance, and recovery quality between high-carb and low-carb training weeks.
- Create a 4-week tracking cycle: 2 weeks of higher carbohydrate intake (4g/kg) during intense training, then 2 weeks of lower intake (1.5g/kg), measuring performance metrics and subjective recovery feelings. Use the app to identify which carbohydrate level supports your best performance and recovery.
This research describes a short-term (4-day) study in recreationally active adults and should not be considered medical advice. The extreme calorie restriction tested (25 kcal/kg FFM daily) is not recommended for general populations and can be dangerous without professional supervision. Anyone considering combining intense exercise with calorie restriction should consult a doctor, registered dietitian, or sports medicine professional before making changes. This study does not apply to people with eating disorders, medical conditions affecting metabolism, or those taking medications that influence hormone levels. Results may differ based on individual factors, training experience, and overall health status.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.