Does BMI effectively indicate obesity in individuals? Can we trust it as the standard for determining whether we are obese, overweight or healthy?

BMI, or body mass index, is so well known by most people as the measure of the health of the body that most people don’t question its authority. It is used by doctors, personal trainers, dietitians and life insurance companies to determine whether or not a person is overweight, healthy or obese.

Unfortunately, BMI has some serious flaws. Ask a serious bodybuilder what he thinks about the fact that his BMI indicates he’s overweight and he’s likely to laugh – these guys often have body fat levels below 10%. It’s not body weight or body mass that’s at issue as far as Type 2 diabetes, cardiovascular disease or hypertension are concerned, it’s fat levels. The fatter you are, the greater the risk of disease. It just happens that BMI has been the accepted tool to determine body composition since 1985. Why? It’s really easy to work out, you just need to know a person’s weight and height then run a simple formula and, voila! He’s “normal”, “overweight” or “obese”.

Here are some interesting BMI facts that might surprise you and should get you thinking about its usefulness (or lack thereof) as a tool you use to determine what shape your body is in:

1. The formula for BMI was devised by Belgian mathematician, Adolphe Quetelet, between 1830 and 1850. He warned that the calculation was only meant to be used for large diagnostic studies on general populations and was not accurate for individuals.

2. The height and weight tables used to determine what your score means came from the life insurance industry initially in 1908. In 1985 the National Institute of Health (NIH) began defining obesity according to the BMI, which defined the 85th percentile for each sex as the official cutoff for “obesity”, based on the standards for underweight, average, overweight and obese that were set by the Metropolitan Life Insurance Company mortality tables. It pays to think about the motives of life insurance companies in using, and determining what would be termed “obese” when drawing up policies – it’s unlikely those “obese” customers got a discount on their insurance premiums.

3. The NIH introduced the BMI standard with the view that it would be only used by doctors to warn patients who were at especially high risk for obesity-related problems. It was never intended that it be used by individuals as a diagnosis of whether or not their weight is healthy but this is how it is used today – individuals are encouraged to easily diagnose their own BMI via the NIH website BMI calculator.

4. The standardized BMI tables (put together by the life insurance companies) fail to take body frame or build into account (“small”, “medium” or “large frame”, for example).

5. The BMI is based on a Caucasian standard and can be inaccurate for other races. Some Pacific Island populations and African Americans in general have a lower percentage of body fat at a given BMI than do white or European populations (Stevens, 2002).

6. In 1998 the NIH reclassified the definition of “overweight” overnight by lowering the threshold by 10 pounds. On Jun 16, 1998, the “average” woman was 5 feet, 4 inches tall and weighed 155 pounds. On June 17, 1998 that same woman became “overweight” as the weight for “average” dropped to 145 pounds. Keep in mind that the much-publicized US obesity crisis has risen to the forefront of national attention only since the late ‘90s, after the NIH changed the standard for what constitutes overweight and obesity.

Does all of this mean there isn’t an obesity problem or that having too much body fat isn’t detrimental to health? Obviously not, but using the BMI as a standard to determine the condition of your body probably isn’t the best idea either. Especially when you realize the definitions for “overweight” and “obese” are arbitrary and at the whim of insurance companies or the NIH and that people with extremely low body fat and in superb physical condition can be labelled as “overweight” per their BMI.

What’s a better way to determine fat levels in the body? The gold standard currently is hydrodensitometry testing and involves getting into a tank of water. Based on the amount of water displaced, your body density and body fat can be calculated. It’s used by universities primarily and costs $25 to $75 per test. Then there’s DEXA scanning, the same imaging technology doctors use to measure bone density to determine osteoporosis risk. Your body fat, muscle and bone mineral density are measured. It’s extremely accurate and non-invasive but costs $200 to $300 per test.

If you’re looking for a simple method to predict heart attack risk and other obesity-related diseases that you can use at home and costs next to nothing, consider checking out your waist to hip ratio. What’s healthy? For men, anything below 0.95. For women, below 0.86 per the American College of Sports Medicine.

Here’s how you find your waist to hip ratio (WHR):

Measure the circumference of your waist just above your belly button
Measure the circumference of your hips around the buttocks (widest point)
You can measure in inches or centimeters
Divide the waist measurement by the hip measurement
WHR = waist circumference/hip circumference

Always remember, exercise is a key factor in alleviating the risk for cardiovascular disease, Type 2 diabetes, hypertension, osteoporosis and many other potentially deadly conditions. You can exercise no matter what shape your body is in now and it will improve so long as you do it properly and consistently. Being educated and seeking advice from exercise professionals to make sure you’re on the right path should be part of your overall health plan.

Tracey Thatcher

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