Myth #3: Carbs Lead to Weight Gain
Runners know carbs are essential for training, but many still cut back if they're trying to lose weight (learn the Right Way to Carbo-Load and avoid unnecessary weight gain.) After all, eating lots of carbs, as you would pre-race, causes the scale to go up. "Carbs act like a sponge," says Bonci, "helping you absorb water." That weight is temporary and means you're well fueled. But there's more reason to keep carbs—whole-grain carbs-in your diet. According to a study published in April 2012, participants who ate a low-calorie diet high in whole wheat for 12 weeks lost more fat than a group that ate a low-cal diet high in refined wheat, most likely because the extra fiber in whole grains was more filling.
Make it work: "Whenever you eat grains, make them whole," says Katherine Beals, Ph.D., R.D., an associate professor at the University of Utah. To make this a reality, cook a large batch of grains to eat all week. Add different nuts, dried fruits, vegetables, and meats to vary the flavors.
Myth #4: Cut All Fat
Fat is the most calorie-dense nutrient, so it would make sense that eating less of it would help you lose weight. But slashing your fat intake may have the opposite effect. In a study published in the Journal of the American Medical Association, researchers compared participants on three diets—low-fat, low-glycemic, and low-carb. Eating a low-fat diet decreased resting energy expenditure (or the number of calories you burn at rest) the most. Cutting back on fat also affected hormones essential to keeping cholesterol and insulin in check. "We need fat for many reasons," says Bonci. "It's an important fuel source for exercise. If you don't consume enough, your body will burn muscle."
Make it work: "When people eat a low-fat diet, they add flavor other ways, like by eating sugar," says Bonci. She recommends 30 percent of your calories come from fat—and two-thirds of that should be the healthy unsaturated kinds from nuts, oils, fish, eggs, and avocados.
Myth #5: You Should Only Use Zero-Calorie Sweeteners
For runners looking to shed pounds, using zero-calorie sweeteners, such as sucralose, aspartame, and stevia, may be an appealing choice, since swapping out a sugar-packed soda for a diet version is an easy way to cut calories. But according to a joint study statement by the American Heart Association and the American Diabetes Association, the scientific evidence connecting zero-calorie sweeteners with long-term weight loss is inconclusive. Why? One of the main problems is overcompensation. If you save 150 calories by drinking a diet soda, but then reward yourself with an extra helping at dinner, you've negated any calorie-saving benefit.
Make it work: "If you drink lots of soda or add tons of sugar to your coffee," says Bonci, "you may want to try diet versions." However, "if using a zero-calorie sweetener gives you license in your mind to eat whatever you want, then it's not the right choice for you. You have to make sure cutting back in one arena doesn't prompt you to overdo it in another."