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Your Body Fat Percentage: What Does It Mean?

The bathroom scale is a standard tool for anyone trying to get into better shape. Many either dread or antcipate what that little scale will say. But can the scale tell you the whole story? While it’s always a good idea to keep tabs on your weight, it’s also important to understand what makes up your weight. Body composition refers to the amount of fat you have, relative to lean tissue (muscles, bones, body water, organs, etc). This measurement is a clearer indicator of your fitness because regardless of what you weigh, the higher percentage of 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.

Overfat Versus Overweight
Your body mass index (BMI) is a measurement that 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 Conan the Barbarian). 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.

Measuring Your Body Fat
There are several ways you can find out your percent of 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 US 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 technologies include:

Underwater Weighing — Under water, lean tissue sinks and fat floats. 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. The Bod Pod also 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. It 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, AND exercise, 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, during exercise and rest, your body burns these fat reserves. Be sensible, however—if you eat too few calories (fewer than 1,400 per day) or cut out all carbohydrates, the weight you lose will likely be fluids and muscle, not fat. In this case the scale will go down but your body fat percentage will go up, rendering you less healthy. 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.

RESOURCES:

Centers for Disease Control and Prevention
http://www.cdc.gov/

National Institute of Diabetes and Digestive and Kidney Diseases
National Institutes of Health
http://www.niddk.nih.gov/

CANADIAN RESOURCES:

Canadian Council on Food and Nutrition
http://www.ccfn.ca/

Canadian Society of Exercise Physiology
http://www.csep.ca/

REFERENCES:

BMI for adults: what does this all mean? National Center for Chronic Disease Prevention and Health Promotion website. Available at: http://www.cdc.gov/ . Accessed on July 23, 2003.

Body composition. Georgia State University website. Available at: http://www.gsu.edu/~wwwfit/bodycomp.html . Accessed on July 24, 2003.

Gallagher D, Heymsfield SB, Heo M, et al. Healthy percentage body fat ranges: guidelines based on body fat index. Am J Clin Nutr . 2000;72:694-701.

Eating 100 fewer calories a day could stop weight gain. Science . American Association for the Advancement of Science website. Available at: http://www.aaas.org/ . Accessed on July 24, 2003.

Weight and waist measurements: tools for adults. National Institute of Diabetes and Digestive and Kidney Disorders website. Available at: http://www.niddk.nih.gov/ . Accessed on /. January 3, 2008.

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.