When protein and calories are fixed, carb and fat intake variations do not meaningfully affect muscle growth in trained individuals.
Original: We Were Wrong About Carbs for Muscle Growth!? (new study)
TL;DR
Evidence shows no significant difference in muscle growth between high-carb and high-fat diets when protein and calories are held constant.
Quick Answer
A new meta-analysis of 11 randomized controlled trials found no statistically significant difference in muscle growth between high-carb and high-fat diets when protein and total calories were held constant. While there was a tiny directional trend favoring higher carbs, the effect was too small to be meaningful or reliable. This means eating more carbs than fats does not provide a meaningful advantage for muscle growth, and mixed diets with balanced carbs and fats are equally effective.
Claims (10)
1. To build the maximum amount of muscle mass while lifting weights, consuming more calories than the body burns is required.
2. When people engage in resistance training, eating protein across four to six meals per day leads to higher rates of muscle protein synthesis than eating the same amount of protein in fewer meals.
3. When doing strength training, consuming more protein leads to greater muscle growth than consuming the same amount of calories from carbohydrates or fats.
4. When carbohydrates are consumed, the body releases insulin, which lowers the rate at which muscle proteins are broken down and slightly raises the rate at which new muscle proteins are made.
5. People who feel more energized during their workouts tend to perform more total exercise, and this higher exercise volume is linked to larger muscle growth.
6. The amount of fat consumed in the diet is associated with changes in testosterone levels in the blood, with higher intake between 50 and 150 grams per day linked to higher levels.
7. When muscle glycogen levels drop below one-third of their normal storage capacity, the molecular signals that promote muscle growth after weight training are reduced.
8. Consuming at least 0.25 grams of fat per pound of body weight each day is enough to support basic bodily functions and the production of hormones.
9. When muscle glycogen levels are much lower than normal, the biological signals that trigger muscle growth after weight training are less active.
10. For people who are already trained, changing the amounts of carbohydrates and fats they eat—while keeping total calories and protein the same—does not lead to meaningful differences in muscle growth over eight weeks.
Key Takeaways
- •Problem: People thought eating lots of carbs was necessary to build muscle, while eating more fat was thought to hurt gains.
- •Core methods: Adjusting carbohydrate intake from low (50g/day) to high (300g/day), adjusting fat intake accordingly, keeping protein and total calories constant.
- •How methods work: Carbs refill muscle energy (glycogen) and trigger insulin, which helps reduce muscle breakdown; fats support hormone production and satiety. But the study found that as long as you're not running out of glycogen, your body builds muscle just as well with either.
- •Expected outcomes: People gained similar amounts of muscle regardless of whether they ate mostly carbs or mostly fats, as long as protein and calories were enough.
- •Implementation timeframe: Each diet phase lasted one month, and results were tracked over multiple months to see consistent trends in strength, pumps, and recovery.
Overview
For decades, bodybuilding nutrition has promoted high-carbohydrate, low-fat diets as optimal for muscle growth, based on insulin's anabolic effects and glycogen's role in workout performance. However, a new meta-analysis challenges this assumption by testing whether varying carbohydrate and fat intake—while holding protein and total calories constant—affects muscle hypertrophy. The study reveals that neither high-carb nor high-fat diets produce a statistically significant advantage, suggesting that balanced macronutrient ratios are sufficient for muscle gain.
Key Terms
How to Apply
- 1.Set your daily protein intake to 1 gram per pound of body weight (e.g., 200g for a 200lb person).
- 2.Set your total daily calories to a slight surplus (e.g., 250–500 kcal above maintenance) to support slow muscle gain.
- 3.Start with a low-carb, higher-fat diet: consume 50g of carbs per day and make up the rest of your non-protein calories with fats.
- 4.After one month, increase carbs by 50g (to 100g/day) and reduce fat by 20g to maintain total calories.
- 5.Repeat this process every month: increase carbs by 50g and decrease fat by 20g until you reach 300g carbs and ~50g fat (do not go below 50g fat).
- 6.Track strength progression, workout energy, muscle pumps, soreness, sleep quality, sex drive, and overall fatigue using the RP Hypertrophy or RP Diet Coach app.
- 7.Identify the carb-fat ratio where you feel strongest, recover fastest, and get the best pumps—this is your personal optimal range.
- 8.Once identified, maintain flexibility within that range: eat more carbs on training days and more fats on rest days, as long as protein and total calories stay constant.
You will find a personal carb-fat balance that supports optimal muscle growth, strength gains, recovery, and energy levels—without needing to follow rigid high-carb or low-fat rules. Your results will be equivalent to others regardless of your chosen ratio, as long as protein and calories are adequate.
Claims (10)
1. To build the maximum amount of muscle mass while lifting weights, consuming more calories than the body burns is required.
2. When people engage in resistance training, eating protein across four to six meals per day leads to higher rates of muscle protein synthesis than eating the same amount of protein in fewer meals.
3. When doing strength training, consuming more protein leads to greater muscle growth than consuming the same amount of calories from carbohydrates or fats.
4. When carbohydrates are consumed, the body releases insulin, which lowers the rate at which muscle proteins are broken down and slightly raises the rate at which new muscle proteins are made.
5. People who feel more energized during their workouts tend to perform more total exercise, and this higher exercise volume is linked to larger muscle growth.
6. The amount of fat consumed in the diet is associated with changes in testosterone levels in the blood, with higher intake between 50 and 150 grams per day linked to higher levels.
7. When muscle glycogen levels drop below one-third of their normal storage capacity, the molecular signals that promote muscle growth after weight training are reduced.
8. Consuming at least 0.25 grams of fat per pound of body weight each day is enough to support basic bodily functions and the production of hormones.
9. When muscle glycogen levels are much lower than normal, the biological signals that trigger muscle growth after weight training are less active.
10. For people who are already trained, changing the amounts of carbohydrates and fats they eat—while keeping total calories and protein the same—does not lead to meaningful differences in muscle growth over eight weeks.
Claims (10)
1. To build the maximum amount of muscle mass while lifting weights, consuming more calories than the body burns is required.
2. When people engage in resistance training, eating protein across four to six meals per day leads to higher rates of muscle protein synthesis than eating the same amount of protein in fewer meals.
3. When doing strength training, consuming more protein leads to greater muscle growth than consuming the same amount of calories from carbohydrates or fats.
4. When carbohydrates are consumed, the body releases insulin, which lowers the rate at which muscle proteins are broken down and slightly raises the rate at which new muscle proteins are made.
5. People who feel more energized during their workouts tend to perform more total exercise, and this higher exercise volume is linked to larger muscle growth.
6. The amount of fat consumed in the diet is associated with changes in testosterone levels in the blood, with higher intake between 50 and 150 grams per day linked to higher levels.
7. When muscle glycogen levels drop below one-third of their normal storage capacity, the molecular signals that promote muscle growth after weight training are reduced.
8. Consuming at least 0.25 grams of fat per pound of body weight each day is enough to support basic bodily functions and the production of hormones.
9. When muscle glycogen levels are much lower than normal, the biological signals that trigger muscle growth after weight training are less active.
10. For people who are already trained, changing the amounts of carbohydrates and fats they eat—while keeping total calories and protein the same—does not lead to meaningful differences in muscle growth over eight weeks.
Related Content
Claims (10)
To build the maximum amount of muscle mass while lifting weights, consuming more calories than the body burns is required.
For people who are already trained, changing the amounts of carbohydrates and fats they eat—while keeping total calories and protein the same—does not lead to meaningful differences in muscle growth over eight weeks.
When doing strength training, consuming more protein leads to greater muscle growth than consuming the same amount of calories from carbohydrates or fats.
When people engage in resistance training, eating protein across four to six meals per day leads to higher rates of muscle protein synthesis than eating the same amount of protein in fewer meals.
When carbohydrates are consumed, the body releases insulin, which lowers the rate at which muscle proteins are broken down and slightly raises the rate at which new muscle proteins are made.