The simple answer is, Yes and No. When you first lift weights, it is such a shock to your system, you usually lose fat and muscle simulateonously. This is commonly called “newbie gains”. The hormonal reactions are so strong because of the lack of adaption of your body to lifiting weights, that this becomes possible. You will find though that after the first few weeks, that this will stop.

There are a couple reasons why experienced bodybuilders can’t expect to lose fat and muscle simulateonously. The most obvious one is, that you can’t keep losing fat forever! Your body has a natural bf% it goes to at maintenance level calories, called the set point. It will be tough for you to be able to get your body to go lower then your set point. You will have to reduce calories, to get your bf% below the set point(and lose muscle along with it).

The other reason you can’t lose muscle and fat simultaneously is, our bodies are made to preferentially store fat over muscle. The reason for this, is that thousands of years ago, we humans used to go through long famines. We needed that extra bodyfat storage to get us through those. Those who didn’t store a lot of bodyfat, died during these starvation periods.

Bodybuilders who have used steroids, have found that they can lose fat and gain muscle simultaneously, even with a slight calorie surplus. They could gain more muscle however, by just concentrating on eating more calories, instead of trying to do both at once.