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United States Department of Agriculture

Agricultural Research Service

Fatness or fitness: Predicting risk of future illness
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by Hank Lukaski

Have you ever wondered what factors influence the chances that you will develop diabetes, heart disease or some types of cancer? While family history plays a part, your body size, physical fitness and even the amount of fat in your belly are contributing factors.

A common measure of body size is body mass index, or BMI, which is used to determine whether a person is at a healthy weight, overweight, or obese. A BMI of 25 to 29.9 suggests overweight, while a BMI of 30 and above reflects obesity. In addition, excess fat in the abdomen, independent of total body fat, is considered a risk factor for ailments associated with obesity, such as diabetes.

Many studies of people living in different countries have shown that the risk of getting, or dying from, diabetes, heart disease and stroke increases as BMI values get higher than 25. Although it is assumed that the higher BMI reflects increased amounts of body fat, studies find that BMI also is a good predictor of lean tissue and muscle. As you age, the increases in BMI tend to indicate an increase in body fat, unless you lift weights regularly.

In one study, healthy men and women were measured regularly during a 20-year period to find factors that were associated with developing diabetes, heart disease and cancer. The study found that as BMI increased, there was a greater increase in the percent of people who were diagnosed with, and died from, these diseases compared with other people whose BMI increased only a small amount. It was shown that BMI values greater than 25 were a general predictor of risk of developing these chronic diseases.

Being fit is key

Physical activity plays an important role in reducing the risk of developing diabetes and heart disease. In a study, adults who exercised regularly at moderate or high levels had lower rates of these diseases compared with others who did not. Yet, adults with a BMI greater than 30 who exercised regularly lowered their chances of getting sick to a level that was even less than the people who had a normal BMI a rate between 20 and 24.9 but did not exercise.

Among men and women who had elevated blood cholesterol or glucose, or who had high blood pressure, regular exercise stopped the progression to diabetes and heart disease. During a 15-year period, young adults with low levels of physical fitness compared with other adults with higher levels had three to six times more high blood pressure, diabetes and pre-diabetes, even when body fatness was considered. More important, the risk of developing these diseases was markedly reduced when fitness improved.

As mentioned above, in addition to body size and fitness, abdominal fat predicts risk. Fat deposits deep in the abdomen not what you pinch at your waist are the culprit. Exact determination of this fat requires specialized medical equipment. But you can estimate your own risk for excess deep abdominal fat by measuring your waist circumference, which is highly linked with deep fat.

Place a cloth measuring tape on your skin at the top of the big bones of your hips and parallel to the floor. If you are a man and your waist circumference is greater than 40 inches, you are increased risk. The number is 35 inches for a woman.

What am I to do if my BMI and waist circumference are in the danger zones? The answer is easy. Get active. Studies show that exercise (either alone or together with a modest decrease in energy intake) can reduce abdominal and body fat, which will shrink your waist and lower your BMI.

This body remodeling requires 30 to 45 minutes daily, five days a week. You can exercise either the total amount at one time or break it up into periods that add up to the target time. Any activity is a good start. For the best effects, work at moderate to vigorous levels.

Your best guide is your heart rate. Take 220 (theoretical maximal heart rate) and subtract your age; this is your age-adjusted peak heart rate. Multiply the number by 0.6 and 0.75 to get your target heart rate or work intensity zone. If you are a 50-year-old person, the target zone is 102 to 128 beats per minute. Check your heart rate regularly by measuring your pulse at the artery in your wrist, near the thumb.

Before you start an exercise program, speak with your health-care provider.

Many factors contribute to your risk of developing diabetes, heart disease and some cancers. Although BMI values greater than 25 are a factor, this risk can be reduced, but not eliminated, with improved physical fitness by adopting a regular program of physical activity that fits your life style. Consult with your physician about an exercise and diet program to help lower your risk!

Last Modified: 10/4/2006
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