DEAR DR. DONOHUE: Please settle an argument between my mom and me. She insists I eat a “hearty” breakfast before I leave for cross-country running early in the morning. We have to practice before school begins. Practice is at 6:30 a.m. I eat breakfast around 6 a.m.

I find it hard to run when my stomach is so full. She says I need the food for energy. Who’s right? — B.J.

ANSWER: The time of eating and the choice of foods eaten have a big effect on endurance exercise. Elite bicyclists who ate three hours before biking were able to keep at it 30 minutes longer than those who didn’t eat. If the same bikers ate only half an hour before biking, their endurance dropped by 30 minutes.

Your breakfast is very close to your exercise time. A large breakfast that close to practice is not helping you. The food is still in your stomach when you’re running.

At three hours before exercise, the best foods to eat are those low in fat and fiber. Fatty and fiber foods slow stomach emptying. The meal should be high in carbohydrates. The carbohydrates chosen ought to be ones that don’t provoke a great surge of insulin into the blood. Low-fiber, nonsugary cereals, citrus fruits, apples, milk, beans, nuts and pasta are the kinds of foods that best increase endurance. I don’t know how you are going to manage this with such an early-morning practice.

A lighter breakfast is one best suited to your schedule.

You can reach a compromise with your mother. Eat a “hearty” evening meal. Much of the energy from that meal will be stored and available to you the following morning.

DEAR DR. DONOHUE: I work out with a trainer whom I love very much. He has done wonders for me. He says I can lose more fat by exercising less hard. That’s sounds odd. I don’t understand it, but I like the idea. Can you explain? — R.A.

ANSWER: Your trainer is stating the fact that the body switches from burning fat for fuels to using carbohydrates as exercise intensity increases. That is true.

Even though less fat is burned with high-intensity exercise, the overall amount of fat burned is actually greater with such exercise.

Marathon runners don’t run as fast as sprinters, but they run for much longer times. They do burn lots of fat. Most people do not have the opportunity to exercise for such long periods at moderate to low intensity.

If you want an unpleasant fact, exercise is not the best way to lose weight, but it does much good for you. It strengthens your heart, lowers blood pressure and builds muscle tissue. However, it takes hours and hours of exercise to burn much fat. You have to combine calorie restriction with exercise to lose fat.

DEAR DR. DONOHUE: My know-it-all brother says women will never be able to compete equally with men in sports. I think that with training, women can do the same as men. What do you think? — H.M.

ANSWER: Women can and do compete in sports as skillfully as men.

However, it’s impossible to deny that men and women have different kinds of bodies. Even with dedicated training, women are able to reach only 75 percent of what men can reach in strength-demanding activities. Women, again even with training, have slightly lower lung capacities than men.

Women do have skills that compensate for these biological differences.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from www.rbmamall.com.