Nutrition Q&A

Q. I am a 5-foot-5-inch college student who weighs 145 pounds. I recently lost 15 pounds in 10 weeks by eating 1,200 calories a day of foods such as yogurt, soup and frozen dinners and by keeping active (walking and yoga). I am proud of myself for losing the weight but am afraid that if I increase my calories, I will gain the weight right back. I know I need to eat more for good nutrition, but how can I prevent weight gain?

A. You're right that you need to eat more than 1,200 calories a day. Right now, you're eating fewer calories than your body needs simply to sustain itself, let alone perform daily activities and exercise. To estimate your body's basal metabolic rate (BMR), divide your weight by 2.2 to translate pounds into kilograms. For you, that's about 66 kg. Then multiply your weight in kilograms by 0.9. That number -- 59 for you -- is approximately the number of calories per hour your body would burn if you did nothing but lie in bed all day. So, if you burn 59 calories per hour, you burn about 1,416 calories a day. You need to tack on additional calories -- at least 400 -- for daily activity and workouts. (The precise number, of course, depends on how active you are.)

"If your daily calorie intake drops below your BMR, you're starving your body," says Jackie Berning, Ph.D., R.D., a spokeswoman for the American Dietetic Association and an assistant nutrition professor at the University of Colorado in Colorado Springs. "You'll start to waste away lean body mass, which will lower your metabolism."

To avoid regaining the weight you've lost, boost your daily intake gradually, by about 150 calories. Stay at 1,350 for two weeks, and then add another 150 daily calories for two weeks. Increase at this rate until you've reached at least 1,800 calories. Meanwhile, work on choosing more nutrient-dense foods. Yogurt and soup don't have much fiber, and neither do many frozen dinners. High-fiber foods, such as fruits, vegetables and whole grains, can also help.

Q. Will switching to diet soda help me lose weight? I have been dieting a lot lately, but I have not been noticing results.

A. You'll save about 150 calories per can, says Chris Rosenbloom, Ph.D., R.D., spokeswoman for the American Dietetic Association and associate nutrition professor at Georgia State University in Atlanta. But keep in mind that it takes a deficit of 3,500 calories to lose a pound of fat. So, it would take you about 23 days to lose 1 pound. "Switching from regular to diet soda is a good move," Rosenbloom says. "But that alone won't make a huge difference."

If you're serious about weight loss, evaluate your eating habits as a whole. Regular exercise is crucial. You can lose weight by cutting calories alone, but you'll probably gain it back unless you work out. (Also, water and skim milk have more positive health effects than soda. So drink more of these and less soda.)