Sunday, February 05, 2006

Your Body Fat Percentage: What Does It Mean?

Your Body Fat Percentage: What Does It Mean?
by Krisha McCoy, MS

If you have ever tried to get into better shape, chances are you used your bathroom scale to measure your success. The problem with relying solely on your weight as a measure of your fitness is that it doesn’t take body composition into account. “Body composition” refers to the amount of fat you have, relative to lean tissue (muscles, bones, body water, organs, etc.). While it’s always a good idea to keep tabs on your weight, it’s important to realize that the bathroom scale doesn’t tell you everything.

Overfat Versus Overweight
Your body mass index (BMI) is a more accurate snapshot of your fitness than your body weight, since it takes your height into account. Health professionals use BMI to calculate whether a person is underweight, normal weight, overweight, or obese. For most people, BMI is closely associated with the amount of body fat they carry. To calculate your BMI, divide your weight in pounds by your height in inches squared. The guidelines are:

Interpreting Body Mass Index
Weight Status BMI
Underweight Below 18.5
Normal 18.5-24.9
Overweight 25.0-29.9
Obese 30.0 and above

The problem with BMI is that it doesn’t work for everyone. Some people’s weight and height measurements put them in the overweight or even obese category while, in reality, they are very lean and muscular (think Arnold Schwarzenegger). On the other hand, some people’s BMI indicates that they are healthy, when they are actually overfat, with little lean tissue. So, whether or not your BMI indicates that you are overweight, it is important to find out if you are carrying too much body fat. Regardless of what you weigh, the higher percentage body fat you have, the more likely you are to develop obesity-related diseases, including heart disease, high blood pressure, stroke, and type 2 diabetes.

Measuring Your Body Fat
There are several ways you can find out your percent body fat. If you have ever had your body composition tested at a gym or by a dietitian, chances are it was tested with calipers. Calipers are small clamp-like devices that determine the amount of fat you have lying just below the skin by taking skinfold measurements at various locations on your body such as the back of your arm and your waistline. Health professionals use these skinfold measurements in equations that estimate percent body fat.

Calipers are widely used because they are inexpensive and easy to use, but they are less accurate than other methods. University centers and researchers use more sophisticated technologies to measure body fat, and these technologies are beginning to become available to the general public. For example, a number of hospitals in the U.S. offer more sophisticated body fat analyses for a fee. Also, as technology advances and prices decrease, gyms and weight-loss centers are likely to begin offering these services to their patrons. Some newer technologies include:

Underwater Weighing – Because lean tissue sinks and fat floats under water, your underwater weight can be used to estimate the amount of fat mass you carry. Underwater weighing is highly accurate, but it is expensive and time consuming, and requires special equipment.
The Bod Pod – This machine works by measuring the amount of air your body displaces. Like underwater weighing, the Bod Pod is highly accurate, but it is still expensive and requires special equipment. The Bod Pod is, however, slightly more convenient than underwater weighing, since it doesn’t require underwater submersion and takes less time.
Dual X-ray Absorptiometry (DEXA) Scan – A DEXA scan uses low-level x-rays to calculate the amount of body fat, muscle, and bone in your body. The advantages of a DEXA scan are that it is quick and it takes bone into consideration when comparing body fat to muscle.
Bioelectrical Impedance – This method works by measuring the speed of an electrical current as it travels through your body. It is one of the least expensive methods of measuring body fat and is less subject to human error than calipers, but its accuracy depends on a number of factors, including hydration, the fullness of the stomach, and how recently a person has exercised. If you are looking for a way to keep track of your body fat percentage at home, you can buy a bioelectrical impedance scale. They are more expensive than traditional bathroom scales, but are gradually becoming more affordable. Keep in mind though, that these scales are not always accurate, and are probably better for monitoring changes in your body fat than giving you precise numbers.

Healthy Body Fat Percentages
So, what should your body fat percentage be? A study in the American Journal of Clinical Nutrition published the following guidelines based on your sex and age:

Body Fat Guidelines
Age Healthy Body Fat % (Women) Healthy Body Fat % (Men)
20-39 21-32% 8-19%
40-59 23-33% 11-21%
60-79 24-35% 13-24%

As you can see, women naturally have a higher body fat to lean tissue ratio than men, and body fat naturally increases with age.

Reducing Your Body Fat
When it comes to losing weight, the key is to eat fewer calories than you expend. If you do this, you will lose body fat. Your body was designed to store fat so it would have reserves of energy during famine; when you take in fewer calories than you expend, your body burns these fat reserves. Be sensible, however—if you eat too few calories (fewer than 1,200 per day) or cut out all carbohydrates, the weight you lose will likely be fluids and muscle, not fat. Lose weight slowly—one to two pounds per week—and continue exercising to maximize fat loss and minimize muscle loss.

A study in the journal Science found that eating 100 fewer or burning off 100 more calories a day could prevent typical weight gain—about two pounds a year, on average. Cutting out or burning even more calories can help you lose some of the extra weight you may already be carrying.


National Institute of Diabetes and Digestive and Kidney Disorders
National Institutes of Health


"BMI for adults: what does this all mean?" National Center for Chronic Disease Prevention and Health Promotion web site.
Available at:
Accessed on July 23, 2003

"Weight and waist measurements: tools for adults." National Institute of Diabetes and Digestive and Kidney Disorders web site.
Available at:
Accessed on July 28, 2003

Gallagher D, Heymsfield SB, Heo M, Jebb S, Murgatroyd PR, Sakamoto Y. Healthy percentage body fat ranges: guidelines based on body fat index. Am. J. Clin. Nutr. 2000;72:694-701.

"Body composition." Georgia State University web site.
Available at:
Accessed on July 24, 2003

"Eating 100 fewer calories a day could stop weight gain, Science authors say." American Association for the Advancement of Science web site.
Available at:
Accessed on July 24, 2003


Last reviewed August 2003 by Rhonda Kaufman, MD

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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