Obstacle #1 You crank the AC

Go green! Here's how it can save (the shape of) your own rear, too: In a study published in Physiology & Behavior, researchers found that exposure to temperatures above the "thermo neutral zone"-the artificial climate we create with clothes, heating, or air conditioning-decreases our appetite and food intake. "At a slightly uncomfortable 81 degrees, the women in the study experienced a 20 percent decrease in appetite and ate 10 percent less than at 72 degrees," says lead author Margriet S. Westerterp-Plantenga, Ph.D., a professor of food-intake regulation in the department of human biology at Maastricht University in the Netherlands.

Detour

Instead of cranking the air conditioner every time you feel a little warm, learn to endure slightly steamier conditions. Hitting the "off" button is well worth a little discomfort if it helps you lose the saddlebags.

Obstacle #2 Always a go-getter, you work out at 6 a.m.

Why not? Morning workouts are great-if you go to bed at 10 p.m. Women who sleep 7 or more hours a night are less likely to put on weight than women who didn't reports a recent study in the American Journal of Epidemiology. Those who slept only 6 hours a night were 12 percent more likely to gain substantial weight-33 pounds on average over the course of 16 years! Women who only slept a short 5 hours had a 32 percent chance of gaining 30 or more pounds.) Other studies have linked lack of sleep to a higher BMI and have found that it negatively affects levels of the appetite-regulating hormones ghrelin and leptin.

Detour

Don't sacrifice your snooze time..not even for an extra-long run. And quality matters more than quantity, so taking a siesta later won't help. "In a 20-minute power nap you don't get into the deep-sleep stage," says Donna Taliaferro, Ph.D., associate professor of nursing at the University of Missouri-St. Louis, who conducts research on sleep and circadian rhythms. "You need to go through the cycles of sleep over a few hours to get the restorative rest that allows your body to work properly." Bottom line: You're better off sleeping through your workout every other day than stumbling to a sunrise Pilate's class on too few zs's.

Obstacle #3 You're a teetotaler (or a sot!)

So what? Alcohol may not be the diet kryptonite you thought it was. Recent research showed that those who have a single drink a couple times a week have a lower risk of becoming obese than either teetotalers or heavy drinkers. Those who consume more than four drinks daily, on the other hand, boost their odds of obesity by 46 percent.

Detour

Go ahead and have a drink; definitely avoid the 245-calorie pina colada. Instead, raise a glass of heart-smart merlot (123 calories per 5 ounces), Light Beer (110 calories per 12 ounces), champagne (88 calories per 4 ounces), or sake (39 calories per ounce). Or mix a 100-calorie cocktail, like vodka and diet tonic or tequila and club soda. "Just make sure you drink it with some healthy food, such as raw veggies with low-fat dip or whole-wheat pita and hummus," advises Dawn Jackson Blatner, R.D., a spokesperson for the American Dietetic Association. Eating slows the rise of alcohol in your blood — and cuts the odds you'll drunk-order the deep-fried mozzarella sticks.