You know the drill: Eat less. Exercise more. Lose weight. For decades, this simple equation has been the cornerstone of most weight loss plans. But for the 60 million Americans considered obese, and with four out of five dieters relapsing within a year, that calories-in-calories-out formula doesn’t seem to add up. Some experts are rethinking traditional rules and focusing on another weight loss factor: imbalanced hormones.

“The conventional wisdom has been that there are no good foods or bad foods—that counting calories and eating everything in moderation is the answer. That’s a myth,” says Frank Hu, MD, PhD, professor of nutrition and epidemiology at Harvard School of Public Health. “Food can heavily influence the hormones and biological pathways that influence hunger, satiety, and fat accumulation, so you have to make wise choices.”

Toronto-based naturopath Natasha Turner, ND, author of The Hormone Diet (Rodale, 2009), explains that in a person with a healthy metabolism, hormones work in a complex symphony to assure you get enough to eat and use the fuel efficiently. The hormone ghrelin tells the brain that you’re hungry; its alter-ego leptin alerts you to put the fork down. When you eat carbohydrates, insulin floods the bloodstream, ushering glucose into muscle cells for fuel and locking any extra glucose into fat cells for later use. When you’re stressed, cortisol temporarily ignites a survival response, prompting you to crave high-calorie foods. Thyroid hormones influence your metabolism and how much energy you have, testosterone builds muscle, and glucagon burns fat.

Unfortunately, age, menopause, chronic stress, or poor diets tend to throw this fragile system into chaos. “I have people come in all the time and say these low-calorie diets that once worked for them just don’t work anymore,” says Jade Teta, ND, coauthor of The Metabolic Effect Diet (HarperCollins, 2010). For the hormonally imbalanced (well over half of U.S. adults), slashing calories and hitting the treadmill can actually exacerbate the problem, raising stress hormones and thus boosting cravings and fueling more belly fat, even in otherwise thin people. The low-cal-and-cardio approach also lowers thyroid hormones, sapping energy and dropping metabolic rate, says Turner. The upshot: “If your hormones are out of whack, no diet plan will succeed.”

What steps are more likely to lead to successful weight loss? Because sleep deprivation can reduce leptin levels, commit to sleeping eight hours a night; focus on shorter, more intense workouts that build muscle and heighten resting metabolic rate; and choose foods that foster fat burning and squelch fat storage. Here’s how.