Dr. Katz
Photo: Mackenzie Stroh 
Q: I am 5' 8" and weigh between 135 and 140. What's the best way to find out how many calories I need to eat in a day? Should I trust the online calculators?
—Laura Hamlyn Cary, North Carolina

A: The only way to know exactly how many calories you should consume is to get tested in a metabolic chamber, an elaborate setup found mostly in research labs and universities. This is far from necessary. Relatively simple formulas can estimate your caloric needs, like the Harris-Benedict equation (it's used in many of the online calculators, and you can find it at weight-loss-for-women-over-40.com/bmr-calorie-needs.htm). Plugging your numbers into the equation—assuming you are moderately active—shows that to maintain a weight of 140 pounds, you should get 2,180 calories per day. But you are right to be a little suspicious; this figure is based on an average basal metabolic rate. If your basal metabolism, which accounts for nearly 65 percent of all calories the body burns, is lower than normal, you need fewer calories; if it's higher, you require more. Another approach is to keep a detailed food diary (nutritional log programs for computers and PDAs may be helpful). The idea is to count your food calories for, say, a week during which your weight is stable. Take the daily average, and that's the number of calories you should aim for.

As a reminder, always consult your doctor for medical advice and treatment before starting any program.