Step 1 revolves around simple math: You must eat fewer calories than your body is accustomed to in order to drop bodyfat. When a calorie shortfall is created, the body responds by digging into body-fat reserves to make up the difference. And presto, you grow leaner. All other laws aside, this one heads the list every time, no matter what dietary approach you take.
At its core, burning fat comes down to the process of lipolysis—the breaking down of fat lipids, explains Seedman. This happens in the mitochondria of the muscles, or the powerhouses of the cells, responsible for generating the energy our cells need to do their jobs. Exercise has been shown to improve mitochondria function, which then promotes fat breakdown, Seedman adds. Plus, working out helps regulate pretty much all the hormones that optimize fat loss.