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.

Myth No. 6: Going on a diet is the best way to lose weight.

The Theory: Switching to a prescriptive plan temporarily is the smartest way to drop pounds.

The Reality: Short-term, you do lose weight on any plan that results in your eating fewer calories. But temporary changes don’t lead to permanent losses. “A diet won’t work if you think of it as doing a different thing for a while and then you’re going to stop doing it,” says Christopher Gardner, an assistant professor of nutritional science at Stanford University School of Medicine. “If you have a new way of eating and think, I’m going to eat like this forever, that’s the way to lose weight.” And keep it off.

The Best Advice: Don’t go on a “diet” — a quick fix that begins on New Year’s Day or before bathing-suit season. Instead, change the way you eat. Find a satisfying eating plan that you can live with long-term, and make sure you’re eating the right amount of calories for weight loss. Then, when you’ve taken off some weight, don’t go back to eating as much as you did before you cut calories. “To maintain a lighter weight, you have to eat a little less than you did to maintain your heavier weight before,” says Gardner.

Besides, dieting alone won’t work as well as dieting plus exercise — a little bit of exercise, or maybe a lot. Since 1994 the National Weight Control Registry has followed and analyzed the habits of successful weight losers (defined as people who have maintained at least a 30-pound weight loss for a year or more). Among its findings: Those who kept weight off exercised — with brisk walking or some other moderate-intensity activity — an average of one hour a day. “One of the most important aspects of weight maintenance is a high dose of physical activity,” says Rena Wing, Ph.D., a cofounder of the registry and a professor of psychiatry and human behavior at the Warren Alpert Medical School, at Brown University.