DEAR DR. DONOHUE: I know you’ve written about percentage of fat in the body. I was mildly interested in it then, but now I’m very interested in it. Will you repeat that article?

I’m starting to obsess about my weight. I have told myself that most of my weight is muscle, but I’m not as sure about that as I once was. I really haven’t done a lot of exercise. I’d like some guidance on this. — R.B.

ANSWER: Body weight as measured on a scale is only a rough guide to body composition and health. Precise body composition determines how much of your weight is fat, how much muscle, how much bone and how much body organs. Visceral fat, the fat within the abdomen that surrounds abdominal organs, is the true bad guy of health. It’s responsible for many conditions like diabetes, heart disease and blood pressure.

Body mass index is a way of determining body composition. Multiply your weight by 703. Divide the result by your height in inches. Divide that result again by your height in inches. That’s your BMI. Normal is a range from 18.5 to 24.9. Overweight is 25 to 29.9. Thirty and above indicates obesity.

For those familiar with the metric system, the calculation is: weight in kilograms divided by height in meters squared.

Body mass index is far from a perfect estimation of body composition, but it is better than information obtained by weighing yourself on a scale.

Another measurement that gives you a better estimate of your health is waist measurement. It’s taken slightly below the navel (bellybutton) at the end of a normal expiration. A man’s waist should be 40 inches or less and a woman’s, 35 inches or less. Waist measurement provides information on visceral fat, the dangerous kind of fat.

If you want to know what percentage of your weight indicates the right amount of fat, an active young man’s percentage of body fat should be around 15 percent of total body weight; a woman’s somewhere between 16 percent and 26 percent. There are ways of obtaining that information, but they’re complicated and impractical for most of us.

DEAR DR. DONOHUE: Please help me out with a practical question. I walk every morning. I consider it a brisk walk. Before walking, I eat a breakfast of a bowl of cereal, one piece of toast and a cup of coffee. Would it be better to walk before breakfast on an empty stomach? — L.Y.

ANSWER: If you’re walking at a moderate pace, around a mile in 17 minutes, you can eat before the walk or after, whichever is more convenient.

A person who plans to do strenuous exercise should allow three to four hours to elapse before exercising if that person eats a large meal. A large meal is one of 1,200 calories or more.

Some benefit does accrue to eating immediately after exercise. For one, you’re able to store more carbohydrate as glycogen after exercise when the body is avid for calories. You’re also able to incorporate more protein into your muscles then.

DEAR DR. DONOHUE: My resting pulse is 80. I have been exercising for six months and run five miles, five days a week. Isn’t that too high of a pulse for me? — R.V.

ANSWER: It’s a perfectly wonderful pulse (heart rate — the two are the same).

When do you take your pulse? Take it in the morning. After the alarm wakes you, stay in bed for five minutes and then take your pulse. The jarring noise of an alarm might make a heart beat faster. Give it a chance to slow down.

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.

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