At present, Body Mass Index (BMI) is the most widely utilized gauge in determining whether a person is overweight or obese. For a long, long time, experts used standard sex and age-adjusted height and weight tables to estimate a person’s “ideal” body weight, but in 1985, the US National Institute of Health recommended BMI to measure obesity because it is a more accurate estimate of a person’s body fat than the traditional tables. In 1997, the World Health Organization jumped on the BMI bandwagon.
How to compute and interpret BMI
You can compute for your BMI by dividing your weight (in kilograms) with the square of your height (in meters). BMI cut-off values vary from country to country. For adult Filipinos and Southeast Asians, they are as follows: Underweight – BMI of less than 18.5; Normal – BMI of 18.5 to 22.9; Over-weight or Pre-obese – BMI of 23 to 24.9; Class I obese – BMI of 25 to 29.9; and Class II obese – BMI of 30 or higher
Limitations of BMI
BMI is a reasonable indicator of body fat, but many experts do not recommend its use as a diagnostic tool. That’s because BMI doesn’t distinguish between fat and muscle—the weighing scale needle moves for both. Broad-framed and muscular people, including athletes, are often labeled overweight by BMI calculations. Yet, they do not have the level of body fat that will threaten their health. BMI also underestimates the threat for people who are skinny but have big bellies. Researches show that belly fat is in fact more dangerous for health than excess fat elsewhere in the body.
Results of a study published in the journal Frontiers in Public Health showed that using BMI as the lone measure for obesity missed 50 percent of cases of people who had what was determined to be the amount of fat that could be dangerous to their health.
If BMI is not a reliable measure of body fat, what is?
There are more exact ways to measure obesity, but they can be expensive. The DEXA (Dual-energy X-ray Absorptiometry) Scan estimates lean tissue, bone, mineral, and fat across regions of the body with amazing accuracy, but it uses x-rays. Another accurate method is with the use of a machine for a bioelectrical impedance analysis, which runs an electric current through body tissue to determine fat composition. The Mayo Clinic meanwhile uses a Bod Pod, which takes measurements based on body volume.
How much body fat is allowable and why is excess fat bad?
On the average, fat accounts for only 14 to 17 percent of the body weight of physically fit male adults and 21 to 24 percent of the body weight of physically fit female adults. Males are obese if fat represents 25 percent or higher and females 32 percent or higher of their body weight.
Excess body fat entails numerous health risks. In fact, obesity is the single greatest contributor to chronic disease and it increases one’s risk of dying prematurely by two to three times. It contributes to the development of type 2 diabetes mellitus, hypertension, high blood levels of cholesterol, gallbladder disease, sexual and reproductive problems, sleep apnea and respiratory problems, osteoarthritis, and some cancers.
Obesity also impairs a person’s quality of life. Excess weight stresses the body’s joints particularly the hips, knees, and ankles, which results in or aggravates osteoarthritis. Excess weight is also a common cause of low back pain and is a predisposing factor to the development of varicose veins.
Practical ways to tell whether you have excess body fat
There are actually practical and fairly accurate ways to find out if you are fat or not. Measure your waist circumference at your belly button. If it is half your height or less, you are healthy, otherwise, you are fat. Alternately, look at your hip to waist ratio. If your waist is bigger than your hips, you are in trouble.
Written by: Eduardo Gonzales, MD