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.

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.

They're your body's secret weapon: Hormones keep your heart thumping, your digestive system churning, and your brain sharp. "Whenever you feel off, your hormones could be the cause," says Scott Isaacs, MD, an endocrinologist at Emory University School of Medicine in Atlanta.

Having low testosterone levels doesn't necessarily make you gain weight, said Scott Isaacs, MD, an endocrinologist, faculty member of Emory University School of Medicine, medical director for Atlanta Endocrine Associates, and author of Hormonal Balance: How to Lose Weight by Understanding Your Hormones and Metabolism. However, when you gain weight, your testosterone levels will decrease. “Obesity is the number one cause of low testosterone,” Dr. Isaacs said. "Taking testosterone alone rarely results in weight loss. Most patients need to change their eating habits.”

What is the difference between synthetic and natural thyroid medications? The main difference is what they are made from. Synthetic thyroid medications are made from levothyroxine sodium while natural thyroid medications are made from dessicated pig thyroid. The other major difference is what thyroid hormones they contain. Most synthetic thyroid medicines, like Synthroid, contain only T4. The natural medications, like Armour contain both T4 and T3. There is a synthetic T3 medication available called Cytomel. Some people take both a synthetic T4 and a synthetic T3 medication to get both thyroid hormones.

I refuse to use them," says endocrinologist Scott Isaacs, an obesity specialist at Emory University in Atlanta. "In my opinion, there's no good clinical data that they actually work, and I have found that patients seem to regain weight as soon as they stop taking them."

"Any time you lose weight, you see improvements in glucose metabolism," says Scott Isaacs, M.D., author of "Hormonal Balance" and a clinical instructor of medicine at Emory School of Medicine. "And anytime you restrict calories, you get weight loss. But if you do something unsustaniable you get fatigue after a while and ultimately gain the weight back." "During a fast, a person can go into starvation ketosis, which reduces appetite. They won't be hungry because of the ketones -- a byproduct of fat -- that masks hunger. But as soon as they do something where they are no longer ketotic, there's a rebound appetite, which can be hard to control," Isaacs says.

Many people gain weight despite eating healthier and getting more physical activity. If you are working hard at losing weight and are not seeing results, you may have a medical problem. We specialize in the medical and hormonal evaluation and treatment of abnormal weight gain and diet-resistant obesity.