GH not only increases fat-burning but is required to build mass and strengthen the immune system. Yet carbs put a damper on GH release, so it's ideal to go to bed under one of two scenarios: on an empty stomach, or, even better, having consumed only protein, no carbs. This allows blood glucose—the high-tech name for digested carbs circulating in the blood—to remain low, which facilitates the rise in nocturnal GH production.
Caffeine and other stimulants do have a down side though. Since stimulants act upon the central nervous system if used too often or for too long of a time period they can begin to cause overtraining effects. These effects would be much the same as if you were working out too long and too often. This can lead to decreased energy, muscle loss, and ultimately, a lowered metabolism since your body will be trying to preserve energy.
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.