Is that mostly based on bodybuilders and their experience whereas overweight people can actually build muscle and lose fat at the same time while keeping up a caloric deficit? (nerdfitness.com)
If you want to gain muscle and lose fat at the same time ketosis or the ketogenic diet is probably the fastest way you are going to do it, if you train regular. (fitness-baron.com)
You can get stronger, build lean muscle and lose fat at the same time while being keto - adapted. (siimland.com)