Most people building muscle should get 20% to 35% of their total daily calories from fat. In practical terms, that works out to roughly 0.5 to 1.5 grams of fat per kilogram of body weight per day. For a 180-pound (82 kg) person, that’s about 40 to 120 grams of fat daily. Going below 15% to 20% of calories from fat can create problems, but pushing above 35% doesn’t offer extra muscle-building benefits.
Why Fat Matters for Muscle Growth
Fat plays several behind-the-scenes roles in the muscle-building process. Your body stores small fat droplets inside muscle cells, and these serve as a dense energy source during exercise. Training actually increases the number of these droplets near the parts of the cell that produce energy, giving your muscles better access to fuel when they need it most.
Fat is also the only way your body absorbs vitamins A, D, E, and K. These aren’t just general health vitamins. Vitamin D directly regulates muscle cell function, and vitamin K deficiency has been linked to muscle weakness. Without enough dietary fat, you absorb less of these vitamins from everything you eat, which can quietly undermine recovery and performance over time.
The Recommended Range
The American College of Sports Medicine recommends athletes keep fat at 20% to 35% of total calories, which aligns with general health guidelines. For bodybuilders in their off-season (the phase specifically focused on gaining muscle), sports nutrition researchers recommend the same 20% to 35% range, translating to 0.5 to 1.5 grams per kilogram of body weight per day.
Here’s what that looks like at different body weights and calorie levels:
- 150 lbs (68 kg): 34 to 102 grams of fat per day
- 180 lbs (82 kg): 41 to 123 grams of fat per day
- 220 lbs (100 kg): 50 to 150 grams of fat per day
Where you land within that range depends on personal preference and how you split the rest of your calories between protein and carbohydrates. As long as protein is sufficient (typically 1.6 to 2.2 g/kg) and total calories support growth, the exact fat-to-carb ratio is flexible.
The Floor: Don’t Go Too Low
Dropping fat below 15% to 20% of your calories is where problems start. Very low fat intake makes it harder to eat enough total calories, since fat is the most calorie-dense macronutrient at 9 calories per gram. If you’re trying to be in a caloric surplus to gain muscle, cutting fat too aggressively works against you by making meals less energy-dense and less satisfying.
There’s also the vitamin absorption issue. Chronically low fat intake reduces your uptake of fat-soluble vitamins, which can impair recovery and muscle function. Some nutrition researchers recommend physique athletes keep fat at a minimum of 10% to 25% of calories to allow for individual variability, but they caution strongly against staying at the very low end for extended periods.
Fat and Testosterone
One common concern is that low-fat diets will tank testosterone levels, killing your ability to build muscle. The relationship is more nuanced than that. While some studies in general populations have found a correlation between dietary fat and testosterone, research specifically in bodybuilders suggests the connection is more about total energy availability than fat intake itself. In other words, eating enough calories overall matters more for keeping testosterone levels healthy than hitting a specific fat number. If you’re in a caloric surplus and eating at least 20% of calories from fat, testosterone is unlikely to be the limiting factor in your muscle growth.
High Fat vs. High Carb for Gaining Muscle
A 12-week study in strength-trained men compared a low-carb, high-fat diet against a low-fat, high-carb diet while keeping total calories and protein matched. The result: no significant difference in lean mass changes between the two groups. Both diets maintained muscle mass equally well over the study period. The researchers concluded that when energy and protein needs are covered, the split between carbs and fat doesn’t meaningfully affect body composition.
This finding lines up with the broader position from the International Society of Sports Nutrition, which states that a wide range of dietary approaches, from low-fat to low-carb, can be similarly effective for improving body composition. The practical takeaway is that you have real flexibility here. If you prefer fattier foods like eggs, nuts, and avocado, you can lean toward the higher end of the range. If you perform better with more carbohydrates fueling your training, keep fat moderate and allocate more calories to carbs.
Omega-3s and Muscle Protein Synthesis
Not all fats contribute equally. Omega-3 fatty acids from fish and fish oil have a specific benefit worth noting. In a controlled trial, eight weeks of omega-3 supplementation (about 1.86 grams of EPA and 1.50 grams of DHA daily) significantly increased the rate of muscle protein synthesis when combined with amino acids and insulin, compared to a corn oil placebo that had no effect. The omega-3 group showed greater activation of the cellular signaling pathway that drives muscle building.
This doesn’t mean you need mega-doses of fish oil. The study used a dose roughly equivalent to eating fatty fish several times per week or taking a standard fish oil supplement. The benefit appears to come from omega-3s reducing inflammation and improving your muscles’ ability to respond to the protein you eat, essentially making each meal slightly more effective at building muscle. Including fatty fish like salmon, mackerel, or sardines a few times per week, or supplementing with fish oil, is a simple way to get this benefit without overthinking your total fat intake.
How to Set Your Fat Intake
Start by setting your protein target (most research supports 1.6 to 2.2 g/kg for muscle building). Then set fat at around 25% to 30% of your total calories as a starting point. Fill the remaining calories with carbohydrates. This approach ensures you’re getting enough fat for hormone health, vitamin absorption, and energy, while leaving plenty of room for the carbs that fuel hard training sessions.
If you find yourself consistently undereating or feeling low energy, bumping fat up toward 35% can make meals more satisfying and calorie-dense. If you’re someone who thrives on high-carb eating and your training performance suffers when fat is too high, bringing it down to 20% is perfectly fine as long as you don’t stay below that floor long-term. The best fat intake is the one that lets you hit your calorie and protein targets consistently while feeling good enough to train hard.