Updated

The honest-to-goodness truth about how to keep your weight under control.

Myth No. 1: Don't Eat After 8 p.m.
The theory: You burn up the food you eat earlier in the day, while late-night calories sit in your system and turn into fat.

The reality: Calories can't tell time. "Your body digests and uses calories the same way morning, noon, and night," says Mary Flynn, a research dietitian at the Miriam Hospital, in Providence. They may sit around a little longer if you eat, then lie on the couch and watch Letterman, but when you move around the next day, your body will dip into its stores. That said, there are other solid reasons to avoid late-night snacking, not least of which is that snacks you grab when you're tired tend to be unhealthy ones.

The best advice: If you often unwind before bed with a bowl of ice cream or buttered popcorn, try cutting the snack out. The calories saved may be enough for you to lose a few pounds a year. If you're hungry, "eat something on the light side, like a piece of fruit or some cereal with milk," says Ellie Krieger, a registered dietitian and the author of The Food You Crave. Night eaters tend to overeat (which leads to weight gain no matter when it's done) because often they've been skimping during the day and come home famished.

Myth No. 2: Eating Small, Frequent Meals Boosts Your Metabolism
The theory: If you keep adding small amounts of food to your fire (the fire being your metabolism), you will keep it going strong and burn more calories overall.

The reality: Food intake has a negligible effect on metabolism. Some foods, including those with caffeine, may slightly and temporarily increase metabolism, but the effect is too small to help you lose weight. What most affects your basal metabolic rate (BMR), the rate at which your body burns calories at rest, is body composition and size. More muscles and bigger bodies generally burn more calories overall.

The best advice: Build up your muscles. A pound of fat-free tissue burns about 14 calories a day, while a pound of fat burns just two to three calories. And while that difference may not sound like a lot, it will certainly help over time. Remember, too, that when you lose pounds, part of that weight is muscle, warns Liz Neporent, an exercise physiologist and the president of Wellness 360, a New York City-based corporate-wellness-consulting company. That's why strength training is even more important if you're on a weight-loss mission. Try lifting weights, or you can maintain your muscles by going to a Pilates, body-sculpting, or power-yoga class two to three times a week.

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Myth No. 3: Pasta Makes You Fat
The theory: When you eat carbohydrates, your body turns them into sugars, which are then stored as fat.

The reality: Carbohydrates per se don't make you fat; extra calories do, whether you eat them in the form of carbs, fats, or protein. Besides, carbohydrates include vegetables, fruits, and whole grains, which are important parts of a healthy diet. In short, the problem isn't pasta but the sheer volume consumed.

"Americans tend to eat too much carbohydrates, fat, and protein. But they overeat carbs most of all," says Barbara Moore, a nutritionist in Clyde Park, Mo., and a spokesperson for the American Society for Nutrition. "You go to a restaurant and you're served three cups of pasta with lots of sauce." Those three cups of pasta can pack up to 600 calories without the sauce.

The best advice: Pasta in moderation is fine. Dietitians recommend two or three ounces of uncooked noodles per person―or half of a one-pound box to serve a family of four. This may look like a puny amount, but try thinking of "pasta as an ingredient, rather than as the basis of a dish," says Mark Bittman, author of How to Cook Everything Vegetarian. "Start with a lot of grilled or sautéed vegetables and maybe a tomato-based sauce. Then add some pasta, sparingly." If you want protein, add beans, chicken or shellfish.

Myth No. 4: Coffee Can Help You Lose Weight
The theory: The caffeine in coffee acts as an appetite suppressant and a metabolism booster.

The reality: While coffee may temporarily squelch your appetite, drinking a couple of cups a day won't have enough of an effect to help you lose weight. Besides, pouring too much coffee into your system―drinking, say, four to seven cups a day―may lead to anxiety, sleeplessness, and an increase in heart rate and blood pressure.

The best advice: Enjoy a cup or two of coffee (or tea) every day, if you please. Just be sure that if you add anything to the brew―like cream, sugar, or cocoa powder―you take those calories into account. What's more, those calories might not make you feel as full as the same number of calories eaten in solid form. Another coffee concern: sleep disruption, which new evidence reveals is linked to weight control. "Every time people feel tired, they think, I have to have a latte," says Liz Applegate, director of sports nutrition at the University of California, Davis. "They become addicted to caffeine on a higher level, and it takes four to six hours to clear out of the system. Sleep is not as good, and you're tired the next day." And probably hungrier, too. At least two studies have shown that when people are sleep-deprived, they produce more of the hormone ghrelin, an appetite stimulant, and less leptin, an appetite suppressant. Not to mention that your resistance to the doughnut's siren song is a whole lot lower when you're pooped.

Myth No. 5: Milk Can Help You Lose Weight
The theory: Calcium helps the body break down fat more efficiently, stimulating weight loss.

The reality: Dairy doesn't appear to have magic properties. A few studies from the mid-2000s concluded that dieters who consumed dairy lost more weight than dieters who did not. But other studies showed no effect, and still others showed a link between high milk consumption and eating more calories.

The best advice: Go ahead and eat dairy products, but stick with low-fat versions, which are lower in both calories and unhealthy saturated fats. Milk products are loaded with calcium, of course, but how much calcium you need is a matter of debate. The government recommends at least 1,000 milligrams of calcium for adults under 50 years old (about the amount in three cups of milk) and 1,200 milligrams for people over 50; however, the Harvard School of Public Health holds that no one really knows the healthiest, safest amount of calcium that adults should consume. If dairy products don't agree with you, you can get calcium from fortified soy milk; fortified orange juice; dark green, leafy vegetables, such as kale and collard greens; and certain fish, such as canned salmon.

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