Research vs Bro-science

Do You Have to Get Fat First to Build Muscle? Myth vs Research

Published: 2026-07-06

Written by: Hirotsugu YoshimuraReviewed by: Tomonobu Someda

'You have to bulk up first to build muscle' and 'you can't gain muscle without gaining fat' are stubborn beliefs around bulking. But is getting fatter really a prerequisite for hypertrophy, or is it possible to add muscle while keeping fat gain to a minimum? We test this using research on body recomposition and rate of weight gain. While our existing article on dirty bulking covers how to eat during a bulk, this one asks a more basic question: do you need to get fat at all?

Let the data settle it.

Round1

Can you only gain muscle alongside fat, or is recomposition possible?

What's said

ジムでの通説、増量文化

To build muscle you must run a big calorie surplus and gain fat. You can't lose fat and build muscle at the same time, so you have to get big (fat and all) first and cut later.

What research says

Body recomposition — losing fat while gaining muscle — is documented across multiple sources.
A review by Barakat et al.
(2020) concludes that recomposition can occur not only in beginners and those with obesity but also in trained individuals.
The keys are progressive resistance training and a sound nutrition strategy with adequate protein — not necessarily a large weight gain.
That said, this is a narrative review, and how much recomposition happens depends heavily on individual factors like training history and body-fat level.

Verdict

'You can't build muscle without getting fat' overstates the case. Especially for beginners or those with higher body fat, there's room to add muscle without gaining weight — or even while losing fat. But recomposition gets harder and slower the more trained you are.

Confidence:Mixed evidence

Round2

Does a bigger calorie surplus mean more muscle?

What's said

ダーティバルク支持の通説

The bigger your surplus, the more building blocks for muscle — so during a bulk, eating as much as possible means more muscle.

What research says

There's little evidence that a bigger surplus adds more muscle.
In an RCT by Garthe et al.
(2013), a group deliberately eating a large surplus and a free-eating group gained the same amount of lean mass — but the larger-surplus group added +15% fat mass (vs +3%), i.e., mostly fat.
In an 8-week RCT by Antonio et al.
(2014), consuming far more protein calories than usual (4.4 g/kg/day) changed neither fat nor lean mass significantly. 'More surplus, more muscle' isn't supported.

Verdict

Increasing the surplus doesn't keep adding muscle — the excess largely becomes fat. Even when bulking, a modest surplus with adequate protein is the more practical way to add muscle while limiting fat gain. Contrary to 'getting fat helps,' the extra fat isn't required.

Confidence:Mixed evidence