BMI, or body mass index, is still the tool health care professionals use to determine whether a patient is a healthy body weight or is at risk of health problems related to being overweight or obese. However, many professionals question the utility of using BMI as a tool. On the plus, side, it’s a quick and easy measurement to make. You simply divide your weight in kilograms by the square of your height in meters. To simplify things, you can plug your numbers into an online calculator and your BMI will be quickly calculated for you.
Yet, BMI, as a measurement, misses the mark in many ways. Since the formula only takes into account your total body weight, it doesn’t distinguish between body fat and muscle. For example, a bodybuilder and an overweight couch potato of the same height have the same BMI if both weigh the same, yet the bodybuilder is mostly muscle. BMI also falls short as a measurement in older people who have lost a lot of muscle. Their BMI may fall in the normal range even though they have an unhealthy body fat content due to muscle loss. Their body weight is predominantly fat.
For these reasons, many experts believe it’s time for an overhaul and a better method for monitoring obesity. Rather than using BMI as a measure of a healthy body weight, one of these three tests might be better.
It’s not hard to measure your waist-to-hip ratio. Simply stand up straight and exhale the air from your lungs. Then, use a tape measure to measure the widest part of your hips. Repeat the measurement at the narrowest part of your waistline. Now, calculate your waist-to-hip ratio by dividing the circumference of your waist by the circumference of your hips. What number did you get?
It matters! A study published by the American Heart Association followed almost half a million men and women. What they found was having a larger waist-to-hip ratio is linked with a higher risk of a cardiovascular event such as a heart attack.
What is a healthy ratio? According to the World Health Organization, men should have a ratio of 0.9 or lower while women should have a ratio no higher than 0.85. The study also showed that a high waist-to-hip ratio is riskier for women than for men.
Waist size, in general, is also a marker for cardiovascular risk. Studies show that people who have a wide waistline have poorer metabolic health and are at higher odds of developing type 2 diabetes and cardiovascular disease. Therefore, you can gain some insight by simply measuring the size of your waist. Research shows that women having a waist size larger than 35 inches are at higher risk of cardiovascular events, while the upper healthy range is 40 inches for men.
Why is a larger waist size risky? It’s a marker for greater quantities of visceral fat, a metabolically unhealthy type of fat linked with insulin resistance. Visceral fat isn’t the superficial adipose tissue you pinch, but deeper fat that clusters in the pelvic cavity and lines the outside of organs. This most dangerous type of fat produces inflammatory chemicals called cytokines that fuel insulin resistance. As you probably know, insulin resistance is associated with a higher risk of type 2 diabetes and cardiovascular disease.
By measuring your waist size, you can get a better idea of whether you’re at high risk for these conditions. However, these waist size parameters aren’t as reliable for men and women of South Asian and Chinese descent, as these ethnic groups have higher levels of adipose fat at a given waist size relative to people of European origin.
Both waist size and waist-to-hip ratio are markers of higher cardiovascular risk and are better at predicting heart disease risk than BMI. Still, many health care professionals use BMI as a screen for whether a person is overweight or obese or is at higher risk of health problems related to body weight. Yet, there’s growing evidence that waist size and waist-to-hip ratio are better markers for weight-related risks.
Body Fat Percentage
Another useful measure is body fat percentage. The most reliable way to determine it is with a DEXA scan, a type of x-ray that determines how much of a person’s body composition is bone, fat, and muscle. A DEXA scan can also tell you the distribution of your body fat. Other reliable ways to measure body fat percentage are underwater weighing or with whole-body plethysmography, also known as Bod Pod. Some exercise clubs and sports clinics offer these two techniques.
Fortunately, there are less cumbersome and expensive ways to measure body fat percentage. You can also use skin calipers to measure skinfold thickness at three or more sites. The average of these values will tell you your approximate body fat percentage. However, the values may be off by as much as 8%, as the accuracy will depend on the measurement technique. Bioelectrical impedance scales you can use at home are also popular. These techniques are most useful as a way to monitor changes in body fat composition over time. It’s important to follow the instructions carefully if you use a body fat percentage scale and, preferably, weigh first thing in the morning after emptying your bladder for consistency. Many factors can alter the results, including how hydrated you are and whether you’re constipated or not.
Body fat percentage offers more information than BMI, as it distinguishes between fat and muscle. Having more muscle on your frame is beneficial from a health standpoint, and because more muscle raises BMI, a muscular person with a high BMI might be labeled as obese when they’re actually quite healthy! In fact, a study published in the American Journal of Clinical Nutrition found that measurement of body fat percentage may better predict future health problems related to weight than BMI. Yet, BMI is still the standard most health care professionals use.
The Bottom Line
BMI is still the standard used by health professionals for monitoring obesity, but you can learn more by knowing your waist size, waist-to-hip ratio, and body fat percentage. Measuring your waist and hip size is straightforward and there are also ways to measure body fat percentage with varying degrees of accuracy.
Waist Circumference and Waist-Hip Ratio. Report of a WHO Expert Consultation. Geneva, 8–11 December 2008.
Science Daily. “BMI Not a Good Measure of Healthy Body Weight, Researchers Argue”
WebMD. “Body Fat Measurement: Percentage Vs. Body Mass”