Significant Differences Between Bmi & Obesity

The body mass index became the medical community's primary way of measuring obesity in the 1980s. The BMI became popular because its formula for determining the correlation between height and weight was the most accurate height-weight formula in predicting people's body fat percentages, according to "Beyond BMI," an article in "Slate" magazine. However, the researcher who touted the BMI as a way of measuring a population's health, Ancel Keys, warned against using it for individual diagnoses.

Explanation

Belgian mathematician Adolphe Quetelet devised the BMI in 1832 because he wanted to define the normal man via statistical measurements. He found that weight changes depended more on height squared changes than other height changes. The BMI's weight divided by height squared equation, renamed the body mass index by Keys in the 1970s, predicts disease risk better than weight and replaced the height-weight table as the standard way of measuring obesity, according to the textbook "An Invitation to Health." The BMI classifies you as obese when your weight in kilograms divided by your height in meters squared is at least 30, overweight when it's 25 to 29.9 and normal when it's 18.5 to 24.9.

Body Composition

The most significant difference between body mass index and obesity is that the BMI doesn't differentiate between muscle and fat. Consequently, BMI measurements can be very inaccurate. "Highly-trained athletes may have a high BMI because of increased muscularity rather than increased fatness," according to the Centers for Disease Control and Prevention's "About BMI for Adults" report. An inaccurate measurement of obesity can have negative ramifications. It can give obese people with low BMIs because they have too little muscle a false sense of complacency and can spur people with high BMIs because they're heavily-muscled to diet unnecessarily.

Gender

The National Institutes of Health established the BMI's obese, overweight and normal classifications in 1985. It had separate standards for men and women, but it put all adults in the same category in 1998, although there is a significant difference between the BMI-obesity relationship in men and the BMI-obesity relationship in women, wrote Singer-Vine. The average fat/weight percentage is 27 percent for women and 15 percent for men, but women aren't nearly twice as obese as men. Women have more fat in their hips and thighs, while men have more in their stomachs. Stomach fat is a more dangerous sign of obesity. Keys also warned that the BMI should consider age because older people have more body fat.

Recommendations

There are more accurate ways of measuring obesity than the body mass index. They all tout waist circumference. Men who have a waist circumference of more than 40 inches and women whose waist circumference is above 35 inches are at increased risk of heart disease, wrote Dianne Hales in "An Invitation to Health." In addition, you can measure your body fat more directly. Hales reports that the simple, inexpensive and popular skinfold calipers test gives a fair measurement of body fat, while the underwater weighing test is very accurate, but complex and expensive.