Body Composition Analysis

What are the Standards for Percent Body Fat?

Body composition refers to the percentage of various types of tissue in the body. A 2-compartment model divides the body into fat and lean components, while a 3-compartment model divides the body into fat, bone, and non-bone lean tissue. For the purpose of deciding whether or not to lose weight, the most important aspect of body composition is percent body fat.

While there is little doubt that percent body fat is more directly related to disease risk than is Body Mass Index (BMI), there have not been studies of great enough scope to directly link body fatness to disease risk. The main reason is that percent body fat is much more difficult to measure than BMI. That is why BMI has been so widely used. However, although BMI correlates well with disease risk when large populations are studied, it is not an accurate measure of body fatness for individuals, as explained on our Body Mass Index (BMI) page.

Knowing your your percent fat would provide you with more information about your health risk than would BMI. The table below, based on a scientific study shows the body fat levels corresponding to the different BMI health risk categories.

Men Aged 20-29

Percent Body Fat

Underweight (BMI<18.5)8138
Overweight (BMI>25)202321
Obese (BMI>30)262826

Men Aged 40-59

Percent Body Fat

Underweight (BMI<18.5)91311
Overweight (BMI>25)222423
Obese (BMI>30)272929

Men Aged 60-79

Percent Body Fat

Underweight (BMI<18.5)111413
Overweight (BMI>25)232425
Obese (BMI>30)292931

The tables reveal some of the following interesting points:

  • BMI does not directly correspond to percent fat. This is shown by the fact that, at the same BMI, percent body fat differs among the racial groups and age groups.

  • At the same BMI, men get fatter as they get older. This indicates a shift in body composition that includes a loss of muscle and a gain in fat.

  • Asians have more fat than whites and blacks at a given BMI. That is why Asians should be alert to risks of diseases such as Type II diabetes at a lower BMI than whites or blacks.

  • For the youngest group, whites and blacks have similar percent body fat, but whites appear to increase their percent body fat faster than blacks as they age.

  • The following table gives the approximate body fat percentages corresponding to the underweight, overweight, and obese categories. Because Asians made up a small proportion of the population used to study BMI vs. disease risk, the white and black body composition data are given more weight. However, the body fat cutoffs apply to Asians as well, and may occur at a lower BMIs than for whites and blacks.

  • Men Aged 20-29

    Percent Body Fat

    Underweight (BMI<18.5)81012
    Overweight (BMI>25)212324
    Obese (BMI>30)262830

The following shows the maximum percent body fat allowed for each U.S. military service:

U.S. Army Males

Percent Body Fat

Age 17-20Age 21-27Age 28-39Age 40+
After Boot Camp20222426
Note on Army standards: Using the above body fat criteria, the Army allows recruits aged 17-20 to be overweight, and those above 20 to be obese. After basic training, those aged 17-20 must be normal weight, but those over 20 may still fall within the overweight category.

U.S. Coast Guard Males

Percent Body Fat

Age 17-29Age 30-39Age 40+
All Males232527
Note on Coast Guard standards: Using the above body fat criteria, the Coast Guard allows its men to fall within the overweight but not the obese category.

U.S. Air Force Males

Percent Body Fat

Age 17-29Age 30+
After Boot Camppoints based on waist sizepoints based on waist size
Note on Air Force standards: Using the above body fat criteria, Air Force recruits must not be overweight. But after boot camp, the Air Force has no specific cutoff for body fat percentage. However, waist size is measured as part of the Air Force physical fitness test and a larger waist results in a lower overall fitness score.

U.S. Navy Males

Percent Body Fat

Age 17-39Age 40+
After Boot Camp2223
Note on Navy standards: Using the above body fat criteria, the Navy allows its men to be slightly overweight.

U.S. Marines Males

Percent Body Fat

All Ages18
Note on Marine standards: Using the above body fat criteria, Marines must fall well within the normal weight standard. The allowable body fat limit does not increase with age making the standard more difficult for aging Marines to attain.

Methods of Estimating Percent Body Fat

None of the following body composition methods for estimating percent body fat are perfect as no direct method exists for measuring body fat content in a living subject. All of the methods involve some assumptions and generalizations.

  • Department of Defense tape measurement: This method is used to estimate the percent body fat of members of the U.S. Army, Navy, Air Force, Marines, and Coast Guard if they exceed the tabular weight-for-height limits. It estimates percent body fat from height and the circumferences of the neck and waist. It has fair predictive value for a man's percent body fat. Waist size is affected by the amount of food and liquid in the stomach, so it is best to do this procedure either in the morning before eating or at least 2 hours following a meal. Otherwise, percent body fat will be overestimated.

  • Skinfold Measurement: These estimate your percent body fat from the thickness of skinfolds at various body sites. A skinfold caliper is needed for such measurement. Professional ones are expensive but less costly ones are available. However, the method is only considered reasonably valid and reliable if an experienced technician makes the measurements. There are several different body fat prediction equations using various numbers of skinfolds, the most appropriate of which will be published here.

  • Underwater Weighing: This 2-compartment (fat and lean) method is considered one of the best body composition methods for estimating percent body fat. Since fat is lighter than bone or muscle, the less you weigh underwater relative to your out-of-water weight, the less dense your body is, indicating more fat. By weighing you both out-of-water and underwater using a precise scale your body volume can be determined. Your body density then equals your weight divided by your body volume. However, before body density can be accurately calculated, the volume of the air in your lungs while you are being weighed underwater must be estimated and subtracted from your body volume. All of this requires specialized equipment and trained personnel. Body density is then entered into an equation to estimate percent body fat. The method is expensive and usually only available in laboratories. It doesn't work well for men uncomfortable with holding their breath underwater.

  • Dual X-Ray Absorptiometry (DEXA or DXA): In this 3-compartment (bone, non-bone lean, fat) body composition procedure, you lie on a table for 10-20 minutes while low-dose x-rays scan your body. The method is based on the fact that fat, bone, and muscle attenuate (weaken) the x-ray beams passing through the body to different degrees. Proprietary (black box) software is used to make the body composition analysis. This is currently considered the best method for quantifying body fat, muscle, and bone. In addition to overall percent body fat, it measures fat and lean tissue in each individual body segment and also provides an estimate of bone density. It requires extremely expensive, specialized equipment and trained personnel,usually available only in a laboratory. Results are affected by body hydration. So it is not a good idea to do such measurement after either heavy sweating or drinking a lot of fluid.

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