by Koren Wetmore

You've tried the latest diets--from low-carb to blood-type plans--and still you're not losing weight. You've stuck to the rules, no cheating, but the pounds refuse to budge. You begin to suspect your body is somehow different from the average dieter's. And, according to experts, you may be right.

"There are so many factors today, it's no longer just a matter of diet and exercise," says certified nutritionist and fitness trainer Lorrie Medford, author of Why Can't I Lose Weight? "Women may also need to reduce stress, balance their hormones and get their blood sugar under control."

For Sara Roth, 43, no amount of dieting worked. She reduced calories and struggled to exercise even though most days she felt exhausted. She tried to lose 10 pounds only to gain an additional 15. "This weight gain showed me something was definitely wrong," Roth says.

She was later diagnosed with hypothyroidism, a condition where the thyroid glands do not produce enough of the hormone thyroxine, which controls the body's ability to break down food and store it as energy. It took six months to regulate Roth's thyroid with medication. "But once the medication kicked in, it was just a matter of doing what everybody else does to lose weight--exercise and eating less," she says.

Weight loss will always be a matter of eating less and exercising more, but if you're doing these things and still not losing weight, you have to face the possibility of an underlying medical condition, says Warren Peters, MD, director of the Center for Health Promotion at Loma Linda University in Loma Linda, Calif. Here's a brief look at some medical conditions that may interfere with weight loss...

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