I got this from Stronglifts newsletter but you can also read it at their website of Stronglifts.com. A comment was left regarding the 5×5 eBook stating the following.

It’s impossible to lose fat and gain muscle at the same time. One requires a caloric surplus, the other requires a caloric deficit.

The only time both may happen is when an overweight individual first begins working out.

This is the reason that professionals go through cycles where they alternate between bulking and cutting.

Stronglifts goes on to discuss this in some brief detail about how it is indeed possible to Lose fat while gaining muscle and sums it up with this.

You can build muscle while losing fat. Just like you can build muscle without gaining weight. Or gain weight without gaining fat. Get stronger, eat healthy. Leave the details to the bodybuilders.

I suggest heading over there to read the full post.