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Calories not the only factor in dieting

Question: I found out to my surprise that a plain bagel (3.5 ounces) and a McDonald's cheeseburger each have about 325 calories. But when I eat a bagel, it seems less fattening than when I eat a cheeseburger. Is it possible that the calories in the bagel are less fattening than those in the cheeseburger, or is it just the wishful thinking of a bagel lover?

Answer: Your intuition is correct. The bagel is less fattening than the burger. This is because turning nutrients into body fat takes energy. For carbohydrates, the cost is 23 percent of the excess carbohydrate calories consumed, and for fat, it's only 3 percent of excess fat calories. Since almost all of the calories in a bagel come from carbohydrates and about half the calories in a cheeseburger come from fat, these storage costs make a difference. The reaction of our bodies toward the form in which calories are consumed is one of the reasons studies often find low correlations between total calories eaten and degree of obesity. (Another reason is that eating excessive fat seems to signal the body to be less wasteful of energy and to conserve stored fat.)

There are two practical implications here. First, we should be as concerned about the kind of food we eat as we are about the number of calories in a particular food. Trying to eliminate as much fat as possible from our diets is one of the most efficient and painless ways of losing weight. It's also a heart-healthier way of eating. So, go for bagels before burgers.

Second, beware of the ever-present and over-sold low-carbohydrate diets. They are usually high in fat, as well as protein, which will eventually defeat their purpose. Keep in mind, too, that even though the initial weight loss from these diets can be impressive _ mainly because carbohydrate deprivation reduces water retention _ the body quickly adjusts, and in a few days water weight is back to normal.

When menstruation stops

Question: I've been hearing more and more about amenorrhea in athletes. Can you tell me something about this problem? Is it dangerous?

Answer: Amenorrhea is the absence or suppression of menstruation. This is a normal condition after menopause and during pregnancy and lactation. However, amenorrhea has also been associated with young women runners, cyclists, gymnasts, swimmers and other athletes. Apparently, intense physical training disrupts the delicate, hormonal functions that regulate the reproductive cycle. And this is not normal. Over time, the condition can cause very serious problems, particularly with bone growth and density.

Two recent studies dramatically illustrate this point. The first found that amenorrheic athletes had about 25 percent less spinal bone mass than their non-athletic peers. The second discovered that the spinal bone densities of young amenorrheic athletes were equivalent to those of 51-year-old women. As a result, as other studies have shown, amenorrheic athletes tend to have more sport-related fractures than do menstruating athletes.

Amenorrhea is potentially a serious problem. Athletes who show signs of the condition should consult a gynecologist. Alterations in training and diet may be necessary. Fortunately, once training is reduced, and any necessary dietary corrections are made, normal menstrual function resumes within about two months.

Patrick J. Bird, dean of the College of Health and Human Performance, University of Florida, draws on a data base of more than 3,800 medical, health and fitness journals in preparing answers to questions in his column. Write with questions to Dr. Bird, College of Health and Human Performance, University of Florida, Gainesville, FL 32611.