4 Hidden Causes of Weight Gain

You're doing everything right, yet your waist keeps expanding faster than a marshmallow in a microwave oven. The trouble might be your hormones:

Thyroid levels -- Hypothyroidism slows down your metabolism, turning it from Lance Armstrong's racing bike into a tricycle. You can't burn calories like you used to.

PCOS, or polycystic ovarian syndrome -- This accounts for unexplained weight gain in 20% of women. It's insulin resistance that's caused by abnormal secretion of a hormone by your ovaries.

Testosterone drops -- Testosterone can fall in older men and postmenopausal women faster than your libido if you gain belly fat, which leads to more fat. Fat in that area converts testosterone to estrogen. Some say that's why fat single men hang out with guys and drink beer in bars -- they have no libido and no aggressiveness to even try a line on a woman. But women with belly fat get libido loss too, as testosterone from their adrenals is a leading stimulator of sex drive. Less testosterone also means less muscle mass, which makes it harder to burn fat (leading to weight gain). The cure: resistance exercise.

Growth hormone dips -- This can decrease as you age or if you don't sleep at least 90 minutes at a time, leading to weight gain. The best ways to boost it naturally: Get the right amount of sleep and exercise.

Some medications can help control these problems as well as the fat that comes along with them. So if you can't figure out what you're doing that's contributing to weight gain -- and you truly aren't eating extra -- it might be worth talking to your doc.