Measuring Body Fat and Body Fat Distribution

We have discussed that BMI may have limitations in predicting body fatness and disease risk, so let’s learn more about other ways we can measure body fat and why body fat distribution may be important.

Measuring Body Fat Content

Water, organs, bone tissue, fat, and muscle tissue make up a person’s weight. Having more fat mass may be indicative of disease risk, but fat mass also varies with sex, age, and physical activity level. Females have more fat mass, which is needed for reproduction and, in part, is a consequence of different levels of hormones. The optimal fat content of females is between 20 and 30 percent of total body weight and for males, it is between 12 and 20 percent. Fat mass can be measured in a variety of ways. The simplest and lowest-cost way is the skinfold test. In a skinfold test, a health professional uses a caliper to measure the skin thickness on the back, arm, and other parts of the body and compares it to normative standards to assess body fatness. It is a fairly accurate method of measuring fat mass, but similar to BMI, it is compared to standards of mostly young to middle-aged adults. Another issue with skinfold tests is that they can be perceived as modestly invasive and uncomfortable procedures since they involve the pinching of subcutaneous fat with a caliper. Because of this, healthcare professionals may choose to avoid using skinfold measurements, especially among individuals who experience body insecurity or body image issues.

Other methods of measuring fat mass are more expensive and more technically challenging. They include:

1. Underwater weighing: This technique requires a chamber full of water big enough for the whole body to fit in. First, a person is weighed outside the chamber and then weighed again while immersed in water. Bone and muscle weigh more than water, but fat does not—therefore a person with a higher muscle and bone mass will weigh more in water than a person with less bone and muscle mass.
2. Bioelectric Impedance Analysis (BIA): This device is based on the fact that fat slows down the passage of electricity through the body. When a small amount of electricity is passed through the body, the rate at which it travels can be used to determine body composition. These devices are also sold for home use and are commonly called body composition scales.

3. Dual-energy X-ray absorptiometry (DEXA): This can be used to measure bone density. It can also determine fat content via the same method, which directs two low-dose X-ray beams through the body and looks at the amount of energy absorbed from the beams. The amount of energy absorbed is dependent on the body’s content of bone, lean tissue mass, and fat mass. Using standard mathematical formulas, fat content can be accurately estimated.

Measuring Fat Distribution

Considering body fat distribution is also important for health. You may have heard that fat on the hips is better than fat on the belly—this is true. Fat can be found in different areas of the body and it does not all act the same, meaning it differs physiologically based on location. Fat deposited in the abdominal cavity is called visceral fat and is a better predictor of disease risk than total fat mass. Visceral fat releases hormones and inflammatory factors that contribute to disease risk. The only tool required for measuring visceral fat is a measuring tape. The measurement (of waist circumference) is taken just above the belly button. Men with a waist circumference greater than 40 inches and women with a waist circumference greater than 35 inches are predicted to face greater health risks.

The waist-to-hip ratio is often considered a better measurement than waist circumference alone in predicting disease risk. To calculate your waist-to-hip ratio, use a measuring tape to measure your waist circumference and then measure your hip circumference at its widest part. Next, divide the waist circumference by the hip circumference to arrive at the waist-to-hip ratio. Observational studies have demonstrated that people with “apple-shaped” bodies, (who carry more weight around the waist) have greater risks for chronic disease than those with “pear-shaped” bodies, (who carry more weight around the hips). A study published in the November 2005 issue of Lancet with more than twenty-seven thousand participants from fifty-two countries, concluded that the waist-to-hip ratio is highly correlated with heart attack risk worldwide and is a better predictor of heart attacks than BMI.^[1] Abdominal obesity is defined by the World Health Organization (WHO) as having a waist-to-hip ratio above 0.90 for males and above 0.85 for females.