If your body’s engine is running at full-speed, there’s little you can do to boost your fat-burning potential – you’re already performing at peak. But if your tank is teetering on half-empty, there’s room for improvement. Use these 7 secrets to shift your metabolism into high gear.Ladies, start your engines!Secret #1: Get more sleepThe number of zzz’s you catch can have a big effect on your waistline. Research shows that sleep deprivation can send your hunger and appetite hormones out of whack.A four-year joint study by the University of Wisconsin and Stanford University found that adults who regularly slept for only five hours a night increased their levels of hunger-inducing ghrelin by 14.9% and lowered their levels of appetite-suppressing leptin by 15.5%.