All About Body Fat Measurement

Body Fat Measurement for Health and Sports

By Paul Rogers

Determining your body fat percentage is useful for weight management, bodybuilding, sports training, and health risk assessment. You can find out:

1. Approximately how much body fat you have
2. If you have too much body fat
3. How your body fat may affect your health risk

How to Use Body Fat Knowledge

It's worth knowing that all body fat measurement methods have limitations. Some tools, like body calipers, may not sufficiently evaluate the fat that is stored around internal organs (visceral fat). This type of fat increases risk for heart disease and diabetes more than fat stored in tissue just under the skin. Further, individuals who are on the overfat side but who exercise consistently may be fitter and perhaps healthier than, for example, a skinny smoker who does not exercise.

Although you should feel free to monitor your body fat for fitness and weight management purposes, your doctor (perhaps with the assistance of a nutrition professional) is the best person to make health risk assessments. He or she will take all of your disease risk factors into account, such as blood cholesterol, glucose measurements, body fat, and fitness level.

Body Fat Charts

Defining absolute “healthy” body fat levels is less desirable than setting ranges of acceptable fat percentages. Women naturally carry more body fat than men, and a healthy range could be from 18 to 25 percent for relatively inactive women and 12 to 20 percent for athletes and fitness enthusiasts, although the distinction is contrived. For men, 12 to 18 percent for non-athletes and 5 to 12 percent for fitness enthusiasts are the normal ranges, even though some charts have higher maximums. For men and women over age 40, the percentages are usually adjusted upward, although this needs reviewing in my view.

Frankly, many of the professional body fat charts project an unfortunate spin on body fatness even though they are only meant as a guide. Some use categories like “underfat," “healthy,” "lean,” or "ideal.” In my opinion, that suggests that being in the "underfat" or "lean" sectors is unhealthy. This is just untrue for many fit people. I don’t accept that a 20 year-old woman with 15 percent body fat who runs more than six miles in 50 minutes and deadlifts 100 pounds should be categorized as underfat and by inference, unhealthy. The notation in these charts is plainly unhelpful and needs updating that's in line with current community standards of health and fitness.

One point to note is that women who get down to around 12 percent body fat experience hormonal disturbances that may result in loss of periods, bone loss, and disordered eating. This is called the “female athlete triad” in sports medicine. Endurance athletes and some women strength trainers may compete effectively at this body fat level, so this is not necessarily unhealthy. But it does require the management and advice of a sports medicine professional.

Body Mass Index or BMI

The body mass index is a body weight and height formula designed to provide a snapshot of your body fatness. It is calculated by dividing your weight in kilograms by your height in meters, squared. The easiest way to calculate this is to use an online calculator like this one from the US Heart Blood and Lung Institute. It allows you to calculate your BMI using pounds, feet, and inches as well as in kilograms and meters.

The BMI categories of are as follows:

• Normal weight = 18.5 to 24.9
• Overweight = 25 to 29.9
• Obese = 30 or greater

The BMI gets consistently criticized by exercise professionals because, like the charts above, athletes or other heavily muscled people are not factored in. That tends to skew the results by placing bodybuilders and heavily built people in the overweight category.

In a sense, this criticism is unjustified because the BMI is only one tool in the hands of experienced health professionals. A keen eye plus a waist measurement is often all that is required to establish if someone is overweight.

Waist Measurement

Waist measurements have evolved to be a useful risk assessment tool for both men and women. Naturally, a thin waist does not a healthy person make--you could be malnourished or ill from any number of chronic diseases. Yet waist measurements--being a measure of body fatness--can be indicative of one's risk of chronic diseases such as heart disease, metabolic syndrome, and type 2 diabetes.

Healthy waist measurements Here are the healthy waist sizes for men and women based on the International Diabetes Federation consensus worldwide definition of metabolic syndrome:

• Caucasian men: 37 inches (94 centimeters)
• Caucasian women: 31.5 inches (80 centimeters)

Values for other groups may be different; Asians' may be lower while those for Pacific Islanders may be higher.

That sounds slim, doesn’t it? And it is, but don’t panic. The best way to apply this is to consider that your risk of metabolic syndrome, and subsequently heart disease and diabetes, will start to rise as you exceed these baselines. And your other disease risk factors play into this, as well.

Waist to Hip Ratio

The waist to hip ratio compares the measurement of the narrowest part of the waist to the broadest section of the hips. Measure your waist between the rib cage and the hip bone as viewed from the front. The broadest hip/butt measure is best estimated from the side. Do not pull in your stomach while taking your measurements.

Divide the waist measurement by the hip measurement. The ratio should not be more than 0.9 for men and 0.8 for women. For example, a man with a 44-inch waist and 42-inch hips would have a waist/hip ratio of 1.05. As a health indicator, some health practitioners consider this ratio superior to outright waist measurement, especially for heart disease risk assessment. One study found an increased risk of heart disease when this ratio exceeded 0.8 for women and 0.9 for men.

Body Weight and Height Charts

Charts that plot height and weight are used to indicate body mass index. They may also represent healthy weight ranges for men and women. You can see these hanging in many doctors’ and dietitians' offices. Some may be enhanced by including extra information on body frame, age, and more.

Charts are useful tools for getting a snapshot. But to get a more accurate evaluation of health risk in relation to body fatness, other factors need to be considered, too.

Body Calipers

Body calipers are used to measure skinfold thickness at various sites to estimate body fat percentages. Because the degree of error is potentially high, this method of fat measurement is just about useless if not in the hands of an expert-–and that means someone with a lot of practice and validation in order to judge the correct places on the body and the right amount of skinfold to capture. A quality pair of medical calipers is a good start. 

Bioelectrical Impedance Analysis (BIA)

BIA uses a small electronic pulse that passes through muscle and fat at different rates. However, its measurements may be thrown off by how hydrated you are and how much you've eaten; it may be too inaccurate for anything other than comparative use. Users are encouraged to establish a baseline measurement and repeat measurements under consistent conditions over time to detect changes. Tanita is a popular brand.

DEXA Scanning

DEXA stands for dual energy x-ray absorptiometry and is sometimes simply called DXA. DEXA is most often used to measure bone density and lean mass, but it can also deliver fat mass readings. The system uses a body scanner, and the process can take about 15 minutes and cost upward of $100 depending on where you live and the availability and use of such technology. It appears to be quite accurate within about a 3 percent error.

Water Weighing

Essentially this entails dunking you completely underwater while you sit on scales and expel all air from the lungs. The technology is based on the displacement of water and the different density of fat and lean muscle mass. This is also an accurate method, although mainly restricted to academic and research establishments because of the enveloping nature of the procedure.

The Bod Pod

This device has been around for about 10 years and may be the best of all. The Bod Pod is an egg-shaped cocoon within which you are enclosed for about 5 minutes. It works on the same principle as water weighing except you displace air instead of water. It's called "plethysmography". No mess, no fears of drowning. It is reported to have an estimated error of only 2 percent.

Summary

You don’t necessarily need a measure of body fat to know you’re making progress on a diet and exercise program. For bodybuilders and sportspeople with critical standards for body fat, measurement may be more crucial. Sometimes though, it helps to know that you are losing fat and holding on to, or even gaining, muscle. Ordinary bathroom scales do not necessarily reflect this.

Sources
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Brunet M 2nd. Female athlete triad. Clin Sports Med. 2005 Jul;24(3):623-36, ix. Review.

International Diabetes Federation. The IDF Consensus Worldwide Definition of the Metabolic Syndrome. www.idf.org/

Welborn TA, Dhaliwal SS. Preferred clinical measures of central obesity for predicting mortality.Eur J Clin Nutr. 2007 Feb 14.

Alvarez VP, Dixon JB, Strauss BJ, et al. Single frequency bioelectrical impedance is a poor method for determining fat mass in moderately obese women. Obes Surg. 2007 Feb;17(2):211-21.

Vescovi JD, Zimmerman SL, Miller WC, et al. Evaluation of the BOD POD for estimating percentage body fat in a heterogeneous group of adult humans. Eur J Appl Physiol. 2001 Aug;85(3-4):326-32.