If muscle is more “expensive” than fat, and if, when pushed, the body will jettison muscle before fat, how do you lose the fat and keep the muscle? Thanks.
Taking creatin as a daily supplement is recommended to both body builders and gastric-bypass patients. It is harmless, not very expensive, and can be bought at any health store.
I can’t take creatine as I have a slight kidney disorder, I’m afraid. Doctor’s orders 
Exercise will convince your body to maintain or even build muscle. If you burn more calories than you consume daily then your body will dig into its fat stores to fuel itself while maintaining the muscle IF you exercise.
That’s what boxers often have to do when they move up a weight division - put on muscle while simultaneously stripping down their body fat. The answer, basically, is eating a lot of food, but making sure it’s the right diet and coupling it with the right physical workouts.
A boxer who’s putting on weight will often have a diet that’s about 6-7 medium sized meals a day, heavy on the meat and vegetables (500g of cooked chicken breast or steak and a plate full of raw vegetables, with a liter of water, for instance). Supplements might have an effect at the margins but putting on muscle and losing fat is not a product of supplements, it’s a product of diet and workout program.
This is a description of David Haye’s diet when he’s in training. (Granted he lost last night, but anyone who can put on 17lbs and still look like this is probably a good model to follow).
- Lose the fat mass slowly enough.
- Include resistance exercises, such as weight training, and mix it up. Include some intensity. If you want muscle mass you need to push the higher weights lower rep end of the spectrum, but still do other work outs too. (The little that creatine might do is allow an athlete already pushing their intensity during a work out to get a small bit more intensity per session. That can translate to a small additional gain, which at that very competitive level may make a difference. Short of the elite level people who use it are fooling themselves.)
- Make sure you get in some protein within the anabolic window of the work out. Studies show good results with such a snack either immediately before or immediate after the weight training work out. Either one can work. More than an hour after and there is less benefit.
- Eat breakfast.
- Lean protein, nuts and seeds, veggies, fruits, overall low fat and fewer and more complex carbs … you know that drill.
Yes, pretty much what Broomstick and isaiahrobinson said. You don’t need to work out and eat like David Haye’s, but scaling down that idea. And a scientific citation supporting the claim is always nice.