Most people are familiar with calories but few know exactly what they are. Calories are units of measure assigned to foods to show how much energy it contains. Your body expends a certain number of calories as energy everyday. If you consume more calories than you expend, the excess will be stored as body fat. If you consume less than you expend everyday your body will have to use stored body fat to meet energy needs.
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.