Katmandu, Nepal: My belly is getting bigger and bigger, which is giving me a backache. I am 28, my height is 5 feet 8 inches and I weigh 176 pounds. How can I reduce my belly without consuming much time? I am a banker and have no time to go for regular exercise.
Dr. Harvey Simon: Your height and weight give you a body-mass index (BMI) of almost 27—overweight, but not yet obese. Still, if your excess weight is mostly in your belly, you're asking for trouble. Excess abdominal fat is a strong risk factor for heart attacks, strokes and diabetes. Based on new research, I now pay more heed to my patients' waist measurements than their BMIs. Risk begins to mount at a waist size above 31 inches for women and 37 inches for men; measurements above 35 inches for women and 40 inches for men are in the danger range. Don't waste your precious time on "spot reducing" gizmos. Even liposuction is a bust; it doesn't remove fat from the abdominal organs, where it's most dangerous.

To reduce, eat less. Avoid calorie-dense foods that are high in fat and/or sugar. Substitute fruits, vegetables and whole grains, which are filling but not fattening.

You also need to exercise more. Build physically active tasks into your daily life. Climb the stairs to your office, walk to the store, do your own chores around the yard and house. Get an exercise bike, so you can burn up calories at home. Give up some sleep to get out for a walk or jog at least a few days a week. You'll be sharper at work, so you'll make back the time you put in.

If you invest some time in exercise now, you'll gain the dividend of good health in the future. You can bank on it.

Minneapolis, Minn.: Should you eat before or after exercise? I get home at about 6 and use an exercise bike or do weight training until 7:30 or 8. Then I have dinner and am in bed by 10. Should I eat first?
Exercise takes energy. That means your heart has to pump more oxygen-rich blood to your working muscles. But when you eat, your intestinal tract also demands more blood to help it digest food and carry nutrients to the rest of your body. To avoid competition between your muscles and your guts, exercise before you eat. It's particularly important advice for people with heart disease and for healthy people who exercise strenuously. For others, a light snack before exercise may be OK, but real eating should be postponed until after real exercise. Although food and exercise don't mix so well, fluids are very desirable indeed, especially in warm, humid weather.

New York, N.Y.: I am 26 years old and run six miles four or five days a week on a treadmill. Can excessive running can cause knee problems later in life? What precautionary measures should I take?
There is a longstanding debate about this, but two 2007 studies help resolve the question. In the first of these, American scientists followed 1,279 healthy adults with an average age of 53. Over the next decade, all the volunteers provided information about exercise, body weight and knee pain, and each had a series of knee X-rays. Researchers found no link between exercise and arthritis.

In the second study, Australian researchers obtained knee MRIs on healthy men and women 50 to 79. People who reported vigorous physical activity over a 10-year period actually had more robust, healthier knee cartilage than sedentary folks.

Cartilage does not have its own blood supply, so it must get oxygen and nutrients from the joint fluid that bathes it. Exercise compresses joints, forcing more nutrients into cartilage. Supplements do not protect joints; even popular products like glucosamine do not stave off arthritis.

Charleston, W.Va.: I have high cholesterol (a total of 280 with high HDL). Statins give me leg pain and fatigue. I already eat a low fat diet and have always done that. Can diet control my problem?
A total cholesterol of 280 is quite high, but if your HDL ("good") cholesterol is also quite high, say above 70, your numbers may be acceptable. You should bring your cholesterol down if your HDL is less robust or if you have cardiac risk factors such as diabetes, high blood pressure, kidney disease, or obesity.

Although most doctors turn to a statin drug to lower cholesterol, you can do quite well without one. Here are three suggestions:

First, improve your diet even more. Instead of reducing all fats, cut down sharply on saturated fats and eliminate trans fats. Both of these fats trick your liver into making more LDL ("bad") cholesterol, and trans fats will also lower your protective HDL cholesterol. Cutting down on dietary cholesterol is less important, but it can help to some degree.

On the other hand, you don't have to deprive yourself of moderate amounts of mono- and poly-unsaturated fats. All this translates to a low intake of animal fat (red meat, whole dairy products), egg yolks, palm and palm kernel oils, coconut milk and partially hydrogenated vegetable oils You can also help yourself by eating more foods that lower your cholesterol. The soluble fiber found in oats, barley, apples, oranges, beans and prunes can really help as can the supplement psyllium.

Other foods that lower cholesterol include soy, nuts and the plant sterols found in spreads such as Take Control and Benecol. Canadian researchers reported that a "portfolio" diet containing these foods lowered LDL cholesterol by 29 percent, almost as much as the 31 percent achieved by a statin drug. And if you enjoy alcohol and can drink responsibly, one drink a day (for women) or two (for men) can help boost your HDL cholesterol.

You should also exercise more, which can help lower your LDL, and is particularly useful for boosting your HDL. Since exercise burns calories, it will help you lose weight, which is great for your cholesterol.

If you still need more help, ask your doctor about non-statin medications. The possibilities include ezetimibe (Zetia), the fibrates (Tricor and Lopid) and the resins (WelChol, Questran, and others). Niacin is also very helpful; unlike the others, it's available over-the-counter as well as by prescription, but like all these medications, it should be used with a doctor's careful supervision.

The statin drugs are so effective that it's easy to forget that there's a lot you can do when a statin won't do.

Vancouver, B.C.: What exercises do you recommend for a 67-year-old male with degenerative neck and lower back arthritis and whose goal is strength, balance and weight loss?
Your goals are excellent, since the human body benefits most from a balanced exercise program. You should build your program around sustained moderate activities that will burn calories, improve your cholesterol, fight diabetes, reduce your risk of certain cancers, lift your spirits and help ward off dementia, and strengthen your heart and circulation. If your arthritis is mild to moderate, you can get big rewards from walking for 30 minutes nearly every day. If walking makes your neck or back feel cranky, you can try swimming or using a low-impact exercise machine such as a stationary bike or elliptical.

To strengthen your muscles and bones, you should add resistance exercises 2 or 3 times a week. You can start by doing squats, chair stands, toe stands and wall push-ups, and then move on to lifting dumbbells as you improve.

Flexibility exercises will help you get limber and reduce your risk of injury. It only takes a few minutes to stretch your major muscles and ligaments. Stretching is a fine way to warm up before and cool down after your daily sustained exercise.Although they are often overlooked, exercises for balance are particularly important for older folks who are at risk for falling. For example, practice standing on one foot, first with your eyes open and later with your eyes closed. Walk a straight line as if you were on a tightrope, putting one foot right in front of the other. Get up from a chair without using your arms.

It's hard to detail exercises for strength, flexibility and balance in a few words. That's why I devoted a full chapter to each in "The No Sweat Exercise Plan." The book offers a simple program for people of any age, and all the exercises can be done at home with very simple equipment. But if your arthritis is severe, I think you should consult your doctor and a physical therapist instead of reading a book. As much as I crave readers, I believe an individualized exercise prescription is best for people with significant medical problems.

Simon is associate professor of medicine at Harvard Medical School, author of "The No Sweat Exercise Plan" (McGraw-Hill) and founding editor of the Harvard Men's Health Watch. For more information, go to health.harvard.edu. Readers should consult a medical professional for an accurate diagnosis.