Willpower, schmillpower. Yes, it's important to maintain healthy habits, but a growing body of research is fingering a handful of hormones for the relentless hunger and overeating that makes some people feel that it's impossible to lose weight. A few under investigation: ghrelin, which stimulates appetite, and leptin and oxyntomodulin, which suppress it. In one study, volunteers who were deprived of sleep saw their levels of ghrelin soar — making them ravenous — while their levels of leptin plummeted. This may explain why people who are chronically sleep-deprived (snoozing less than seven hours nightly) tend to be more overweight than those who get plenty of z's. "Leptin normally signals the brain that your fat stores are large enough, so when levels of the hormone are low, the brain assumes you need more fat and triggers cravings for high-calorie food," says sleep and obesity researcher Gregor Hasler, M.D.
To restore balance: Getting seven to nine hours of shut-eye a night instead of scraping by on just six has been shown to lower your risk of overeating and obesity by 23 percent, in part by restoring your leptin levels. Even just one extra hour of slumber can make a difference. You should also avoid fatty foods, and not just because they're chock-full of calories! Though researchers don't yet understand why, they've found that calorie for calorie, carbohydrates and proteins are significantly more effective at suppressing appetite — and tummy rumbles — than fats. So whenever possible, swap high-fat foods for those loaded with protein and complex carbs such as oatmeal, fresh veggies, and whole grains.
Irritable Bowel Syndrome (IBS)
Some of us get headaches during stressful times, or feel just plain cranky and irritable. But if you carry stress in your stomach instead of your head, it could be because many of the same hormones and neurons are at work in both places — a fact that's led some doctors to dub the gut the body's "second brain." Take serotonin, for example. It's best known as the brain chemical that impacts mood. But 95 percent of the serotonin we produce is actually manufactured in the gut, where it plays a role in digestion. Recent studies suggest that abnormal levels of serotonin may be one cause of irritable bowel syndrome, a condition that causes chronic abdominal pain, cramping, and diarrhea and/or constipation for millions of Americans. "And since up to 90 percent of sufferers are women, some whose IBS symptoms get worse around menstruation, the flux of estrogen and progesterone may also play a role," says gastroenterologist George Arnold, M.D., a clinical professor of medicine at the University of Pittsburgh School of Medicine.