Carbs vs. Fat: Which Helps You Build More Muscle?

A new study compares energy surpluses from peanuts vs. carbs—so, which packs on more lean mass?

If you’ve ever tried to gain muscle, you’ve probably wondered what to eat more of: carbs or fat?

A recent study funded by the Peanut Institute Foundation (yes, that’s real) set out to explore that very question—with peanuts as the fat source and high-carb snacks as the comparison. Researchers recruited 32 experienced lifters—some competitive athletes, some in the military—and had them train three days a week for 10 weeks while eating an extra 500 calories per day.

The two groups—one eating carb-heavy snacks, the other eating peanut-based snacks—both gained weight and muscle. On average, participants added nearly 5 pounds, and 70% of that was lean mass.

That’s a pretty solid return for just three training sessions a week and a modest calorie bump.

But here’s the kicker:The carb group gained more total weight than the peanut group, despite both groups being instructed to consume the same surplus.

The likely reason?

Peanuts may have curbed appetite slightly, or their calories weren’t fully absorbed—a known phenomenon with high-fiber, whole-food fats like nuts and legumes.

What does this mean for your training?

If you’re trying to gain muscle, and especially if you’re a so-called "hard gainer," carbs are your friend. They're easier to digest, less filling, and more readily used for energy—all of which help when you need to eat more than you naturally want to.

Fat sources like nuts (or peanuts, which are technically legumes) can still be useful, particularly if you're looking to slow weight gain or maintain a leaner profile while increasing strength.

Ultimately, both carbs and fats can help—what matters most is consistently eating more than you burn, lifting with intention, and staying patient as your body adapts.

Closing Thoughts from Coaching

In 15 years of helping clients build muscle, this finding matches what I’ve seen in practice. Carbs are almost always the missing piece for those who can't seem to grow, especially when their protein is already dialed in. When we swap out "clean eating" habits that unintentionally limit intake (like too much lean protein or high-volume veggies) with rice, oats, or even fruit juice—muscle finally starts showing up.

Most folks don’t need a mass gainer or a complex strategy. They need enough food, enough sleep, and progressive lifting. And if they want to lean bulk slowly? Nuts, seeds, and whole-food fats keep appetite in check and weight gain smooth.