The hormonal regulation of appetite is very strong. Willpower alone is not sufficient to overcome these biological drives. Thus, medications are increasingly being used because they can help overcome some of the biological changes that drive appetite. And there are more obesity medications available today than ever before.

The two primary hormones that control appetite are ghrelin and leptin. They serve as biological on/off switches. Ghrelin is mainly produced in the lining of the stomach and switches on appetite. Leptin is secreted by fat cells and turns off appetite by signaling when you’re full.

If trying to clean up your diet just leaves you more ravenous and frustrated, you’re not alone. Time to learn how your eating decisions affect your appetite a.m. to p.m.

Produced by fat cells, leptin signals to the brain how much fat is in the body, explains Dr. Scott Isaacs, medical director of Atlanta Endocrine Associates. When leptin levels are low, you tend to feel hungry, and when leptin levels are high, you tend to feel full.

Your metabolism is partly ruled by genetics, but you can rev it up naturally by eating right. Fill up on the following nine foods to increase your body's fat-burning power.

If you store your leftovers in plastic, keep old receipts lying around or think nothing of eating an unwashed grape or two, you could be exposing yourself to chemicals that impede weight loss. "These substances slow your metabolism and increase appetite or alter hormones such as estrogen in the body to cause weight gain," says Scott Isaacs, M.D., an endocrinologist and author of Beat Overeating Now!

Yet another reason not to let your weight seesaw: You'll hamstring your metabolism. "My patients with the lowest metabolisms are the weight cyclers," says Scott Isaacs, MD, clinical instructor of medicine at the Emory University School of Medicine. "When you lose weight, you lose muscle and fat, but when you gain it back, it's mostly fat, which burns fewer calories."

Estrogen helps insulin metabolize blood sugar. So when your levels of the hormone naturally begin to drop as you head toward menopause, this estrogen deficiency increases your insulin resistance, "a condition that causes your body to store the food you eat as fat instead of burning it as energy," Dr. Isaacs explains.

Even if it's been a laze-around-in-your-yoga-pants day, you can still burn more fat for basically no effort by adjusting your thermostat. A recent study in the Journal of Clinical Investigation found that when people were exposed to cold temps for three hours, they burned an additional 250 calories. Your body has to go into overdrive to heat itself up to a cozy 98 degrees, and extra calories are zapped in the process, explains Scott Isaacs, MD, an endocrinologist and the author of Beat Overeating Now! You don't have to walk around shivering to get the benefits, he says; just lower your thermostat by two to three degrees.

Can't sleep? Having memory lapses? Your hormones may be to blame. They can wreak havoc on how you feel, think and function at different times in your menstrual cycle. Luckily, these changes are predictable. By anticipating your hormonal ebbs and flows, you can head off ailments such as cramps and headaches.