Is it possible to gain muscle while being on a calorie deficit?

Question

I know in order to gain muscle you have to be in a calorie surplus, and I know losing fat and gaining muscle don't mix together.

But I'm just wondering why can't it be possible for someone who's in a calorie deficit to gain muscle just by replacing their normal calories with protein and muscle building calories?

Let's say I have to consume less than 1800 calories a day in order to lose fat. Can I hit the gym before one of my main meals, lunch for example, and then instead of having a normal lunch I would take proteins (chicken breast, eggs, potatoes, etc...) so that hopefully I can gain muscles ?

Answer 1

The short answer: No. The more nuanced answer: It depends.

There are two groups that can lose fat and gain muscle at the same time. This is generally true for beginners that have a surplus of bodyfat. And also people who have previously been lean and muscular, but lost it due to inactivity.

Besides those groups you should either be in a caloric deficit to lose fat (keeping protein high to hold on to as much muscle mass as possible). Or being in a caloric surplus to gain muscle.