Instead, leptin's role is to prevent weight loss, and a drop in leptin levels sends the body into survival mode when food is scarce and fat stores decline.

During noted that the most consistent and dramatic finding, however, was a nearly 90 percent drop in leptin, a hormone produced by fat that helps regulate metabolism.

Traditional junk foods tend to be high in sugars and fat. When consumed, these foods will give an immediate boost of energy, followed by a big energy drop.