Can you lose fat and gain muscle at the same time?

Yes. It’s called body recomposition. It shows up clearly in people who are new to lifting, and a 2020 review found it in trained lifters too. You need two things: lifting that gets harder over time, and enough protein. Judge it by your waist and your lifts, since the scale may barely move.

Why people say it can’t happen

Building muscle needs extra material and losing fat needs less energy, so it sounds like you have to pick one. In practice your body can pull energy from its fat stores while protein from your food builds muscle, as long as the muscle is being trained.

It’s like swapping out the furniture in a room. The room weighs about the same, and what’s in it changes.

What the studies found

• Beginners. In an 8-month trial, sedentary adults who only lifted gained about 2.4 pounds (1.1 kg) of lean mass and lost a little fat, with no diet change.
• On a hard diet. In a 2016 trial, young men ate 40% fewer calories and trained six days a week. On high protein, they gained 2.6 pounds (1.2 kg) of lean mass while losing 10.6 pounds (4.8 kg) of fat in four weeks.
• Trained lifters. A 2020 review found many studies showing recomposition in people who already lift, and named the two keys as lifting that keeps progressing and good nutrition.

What to do

• Eat at about your maintenance, or a small cut if you have more fat to lose. The calorie calculator gives you a start.
• Lift three days a week, adding weight or reps when you hit your target.
• Eat 1.2 to 1.6 g of protein per kg of body weight a day, more if you’re already lean. Find your range.
• Measure your waist and log your main lifts every four weeks. If you’re skinny fat, this is where we’d start.