Body Mass Index (BMI) Can't Measure Your Overall Health
Body-Mass index is a ratio of your weight to your height. Too low of a BMI may indicate that you are underweight - undernourished or suffering some kind of illness that leads to unintentional weight loss. Conversely, a higher than normal BMI correlates with being overweight.
What Conditions Are Associated With High BMI?
Having a high BMI correlates with a higher risk for conditions including:
-high blood pressure
But there’s a limit to how useful the BMI is in telling you about the state of your health.
So What's The Limit?
David S. is a 40-year-old art director; he weighs 240 pounds and is 6 foot tall. According to his insurance agent’s BMI calculator, David’s BMI is 32.5, well above the threshold for obesity. David chuckles as he recounts the story of talking with his insurance company about insurance: “Before I went to see her, she must have thought I was a candidate for a heart attack. When I visited, she realized that I wasn’t about to have a heart attack, but I think she almost did!”
In his spare time, David is a body builder. He lifts weights nearly every day, gets regular aerobic exercise in the forms of bicycling and karate, and eats well-balanced meals emphasizing lean meats, vegetables and fiber-bearing carbohydrates. Despite his BMI, his cholesterol levels are healthy, his blood pressure that of an average 25 year old, and his activity level - well, it’s obviously pretty good.
While we’re not all like David, there are two take-home lessons from his story:
1) BMI may not be a good indicator of your health and fitness.
2) A given BMI number suggests that you might be at risk for certain diseases, but it doesn’t guarantee it.
A high BMI does not mean that you have diabetes, cancer, or high blood pressure, nor that you are destined to have one of those conditions. It suggests that you may be at risk, but that’s all.
Because it presumes a certain ratio of body-fat to muscle, it may not accurately reflect whether you have a healthy metabolism, what condition your heart is in, and how you look and feel.
So what indicators should you consider in addition to BMI in trying to determine your state of fitness and what changes you might want to take in your activities and diet? Other risk factors for diseases like diabetes and cancer include:
Just like BMI, no one of these indicators guarantees that you will have, or avoid having, a particular condition. David’s father has a genetic condition that leads to very high cholesterol; David has no cholesterol issues at all. In contrast, another designer, Laurie M., has no family history of high cholesterol, and yet she been taking medication for high cholesterol since she turned 20.
Balance Is Key:
So how do you take all these factors into consideration in designing an exercise and nutritional program that’s right for you? The key is balance. If your BMI is high and you have other risk factors indicating risk for particular diseases, then work with your health care provider to change your exercise type and level, modify your diet, and add medications if needed to reduce the chances of developing the disease in question. If your BMI is high, but your other indicators suggest that you’re healthy, it may be a matter of your comfort - do you like how you feel? are you able to accomplish the activities that matter to you? If so, check with your physician to see whether maintaining your current weight and diet might be just what you need!
Calle EE, et al. “BMI and mortality in prospective cohort of U.S. adults” New England Journal of Medicine, Volume 341 pages 1097–1105, 1999 Centers for Disease Control, “Using the BMI-for-Age Charts,” http://www.cdc.gov/nccdphp/dnpa/growthcharts/training/modules/module1/text, 2005
Garrow JS and Webster J. “Quetelet's index (W/H2) as a measure of fatness,” International Journal of Obesity Volume 9 pages147–153, 1985 Gallagher D, et al. How useful is BMI for comparison of body fatness across age, sex and ethnic groups? American Journal of Epidemiology Volume143, p 228–239, 1999
National Institutes of Health, “Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults,” 1998
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