Taking measure of body-fat test
The tool most commonly used to determine whether people are overweight or obese appears to give some racial groups a false sense of security -- and others unnecessary cause for concern.
The well-known body mass index (BMI) relies on a calculation using height and weight to produce a number. That number enables scientists to gauge the risk of weight-related illnesses such as heart disease, high blood pressure and Type 2 diabetes in populations. A BMI of 18.5 to 24.9 is considered healthy; 25 to 29.9 overweight; and 30 or higher, equal to 186 pounds or more for someone 5 feet 6 inches tall, obese.
But in June, a study of nearly 1,200 people of South Asian, Chinese, Aboriginal and European heritage became the latest to show that current BMI thresholds significantly underestimate health risks in many non-Europeans.
Even when waist size and waist-to-hip ratios were considered, the study found that many in the Asian, Chinese and Aboriginal groups who had “healthy” BMI levels were at high risk of weight-related health problems and didn’t know it.
BMI and other body measurement thresholds “do not apply to non-European ethnic groups, and warrant revision,” concluded Salim Yusuf, director of the Population Health Research Institute at McMaster University in Hamilton, Canada, in the International Journal of Obesity and Related Metabolic Disorders.
This isn’t the first time that the body mass index has been called into question. In 2000, the World Health Organization’s Pacific Group suggested setting a BMI of 23 as the threshold for being overweight and 25 for being obese in Asian populations.
Other studies have found that the index can overestimate risk in African Americans and South Pacific Islanders, populations that generally have a lower percentage of body fat and more lean muscle mass than whites and Asians. For this reason, some scientists believe that for these groups, a BMI of 26 should be the threshold for being overweight and 32 for being obese.
The National Heart, Lung and Blood Institute also cautions at its Internet-based BMI calculator that the measurement is less accurate at determining who is overweight and obese among muscular people, who have a BMI of 27 to 30, as well as among the elderly, who lose muscle as they age and may be fatter than the numbers suggest.
“Many of us have begun to realize that body mass index is a very poor measure of adiposity -- how fat you are -- and how much health risk you face,” Yusuf said.
As scientists note, the BMI is frequently misused by health professionals and the public. It was intended to screen populations, not individuals, said Wilfred Y. Fujimoto, professor emeritus of medicine at the University of Washington’s School of Medicine in Seattle.
Weight-related health risks are best determined, he said, “not only by looking at BMI, but also at what other tests might show,” including waist size, blood cholesterol levels and blood pressure.
Until there’s more scientific consensus, here’s what experts recommend to gauge weight-related health risks:
* Use the BMI as a starting point. Ask your doctor or other health professional to measure blood pressure and levels of blood cholesterol, triglycerides and blood sugar. Don’t assume you’re at elevated risk -- or home free -- based on BMI alone.
* Watch the trend. If body weight, BMI, waist size and other measurements increase, lose some weight to lower them, even if they’re still in healthy ranges. If your blood tests and blood pressure are stable, but your weight and waist are growing, work to maintain your weight.
* Do a stomach check. No matter what your race, gender or age, large abdomens “almost always indicate too much body fat,” Yusuf said.
While you’re at it, measure your waist. Use a soft tape measure. Stand with your feet together, abdomen relaxed. Place the tape measure at your natural waistline, which is the narrowest part of your upper body. Current guidelines are for women to aim for a waist of 35 inches or less; men, 40 inches or less. But Fujimoto and others believe that those of Asian heritage should aim for 30 inches or less for women and 35 for men. For now, other racial groups should aim for the standard goals.
* Decrease risk by staying active throughout the day. Doing so not only burns calories, but can help boost muscle mass, which seems to help lower risk. Even just taking the stairs can help.
At McMaster University, Yusuf takes walking meetings with colleagues instead of going out to lunch with them. In helping to design a new research building, he’s made sure that the elevators are in obscure corners with a sign noting that their use contributes to obesity. Stairs are in an open area of the building to invite walking.
“The key,” he said, “is to build more physical activity into everything you do.”
