Why Your BMI is (Partly) BS

According to the Centres for Disease Control, 40% of American adults are obese. Obesity is a serious health issue, increasing the risk of heart disease, stroke, diabetes and some cancers. But how does the CDC know how many people are obese and how do they measure that? Are you considered obese?

To answer these questions, it helps to understand how Body Mass Index (BMI) was developed and why it is used by doctors, insurance companies and government researchers as a general measurement of body composition and health risk. We’ll also look at some of the ways BMI can be misleading, and we’ll suggest how BMI can be weighed against other simple body fat measurements.

Where Did BMI Come From?

The use of a height-to-weight ratio for measuring obesity began with the 19th century Quetelet Index.    In a 1972 research paper by Dr. Ancel Keys, the old Quetelet index was combined with a modern analysis of subcutaneous fat and adipose density in 7400 European men. Dr. Keys proposed using Body Mass Index as a tool for estimating disease risk based on degrees of obesity.

BMI gave doctors a handy way to turn quick, inexpensive and non-invasive measurements into a general estimate of disease risk. It also gave insurance companies and government researchers a way to gather data on the prevalence of obesity in the general population.

Here’s how your BMI is calculated:

·        Convert your height to inches and square that number

·        Divide your weight by your height squared

·        Multiply the result by 703

The average American male stands five feet nine inches and weighs 199.8 pounds. His height of 69 inches squared is 4761. His weight of 199.8 pounds divided by 4761 is 0.04196597. This quotient times 703 gives us a Body Mass Index of 29.5.  What does a BMI of 29.5 tell us?

Standard CDC Interpretations of BMI:

·        18.49 or Lower = Underweight

·        18.5 to 24.9 = Ideal

·        25 to 29.9 = Overweight

·        30 or Higher = Obese

On the CDC scale, our average American man is very “Overweight” and heading for “Obese”. For American women, the picture is about the same. Our average woman is 63.5 inches tall and weighs 170.8 pounds. That gives her a BMI of 29.78, scoring about the same as her male counterpart.

But given our basic differences in muscle mass and subcutaneous fat, why is the same calculation used for both genders? How can one BMI apply to all ages, body types and world cultures? Health researchers are increasingly skeptical, and have pointed out some definite problems with BMI.

Where BMI Goes Awry

BMI does not account for some important health markers, such as where you live, what you eat, the quality of your sleep, how often you exercise and whether you are exposed to high levels of stress.

BMI relies on body weight, but since muscle weighs 18% more than fat, how accurate is BMI for the body composition of men and women who train with weights? Here are some telling examples:

Obese and Overweight Champions

Leonard Fournette, the NFL running back and star of the 2021 Super Bowl, stands 6 feet even and weighs 228 pounds. That gives him a BMI of almost 31, decidedly in the “Obese” category.

Conor McGregor is the current UFC “Lightweight” champion. His body is so lean and ripped, he looks like a walking anatomy chart. However, his BMI of 25.10 says he is “Overweight”.

The Benefits of Muscle Mass

Not only are Fournette and McGregor definitely not at risk due to their body weight, their extra muscle mass increases their metabolic rate, fortifies bone density, strengthens joints, tendons and ligaments, improves blood flow, enhances balance, and yields many other benefits which reduce health risk. Taken together, these factors make BMI essentially meaningless when applied to muscular individuals.

More Reasons to Question BMI:

·        Is the BMI Formula Sound? Mathematicians have pointed out numerous ways in which the calculation of BMI does not properly reflect human shapes with logical ratios. In general, BMI tends to make short people rank as “thinner”, while tall people skew “fatter”. 

·        Is BMI Biased Toward Europeans? The original study by Dr. Keys was based on the adiposity and subcutaneous fat of European men. More recent studies have noted that Asian men with the same measurements have very dissimilar health states and outcomes.

·        Is BMI Biased Toward Women?  Women generally have more body fat and less muscle mass than men, but even world-class athletes with plenty of muscle, like tennis champion Serena Williams and kickboxer Rhonda Rousey still have BMI numbers in the lower “Ideal” category.

·        Is BMI Relevant for Seniors? Research shows that a supposedly “ideal” BMI of 23 is associated with higher health risks in people over 65. Meanwhile, seniors in the “medium-overweight” range (BMI about 27) have much better health outcomes. This may be because more muscle mass improves metabolism and immunity, strengthens balance and provides more protection in a fall.

Easier Ways to Monitor Body Fat

The CDC stands firm on the value of the correlation between the Body Mass Index and general health, but they also recognize other easy and non-invasive ways to keep an eye on your body fat. Some of these may be better suited to your body type than BMI.

There is no disputing the fact that fat around the abdomen increases the risk of heart disease and metabolic disorders, or that extra fat overworks the liver, heart and kidneys. Here are some of the best ways to forget about BMI, and instead apply the traditional wisdom of watching your waistline.

Waist to Height Ratio – The ideal ratio is 0.5 for both men and women. If you are a typical 69-inch man, your ideal waist measurement is 34.5 inches. If you are a 64-inch woman, your ideal waist is 32 inches.

Waist to Hip Ratio – The ideal ratios are 0.9 for men and 0.85 for women. A woman with a 32-inch waist and 38-inch hips is right in the zone, with a waist-to-hip ratio of just over 0.84

Waist Measurement…Period – This one is really simple. The danger zone for abdominal fat begins at about 40 inches for men, and 35 inches for women.

To learn more about maintaining a healthy body composition, call Future Fitness at (817) 803-4846, or stop by the club at 1919 Golden Heights Road, #100, Fort Worth TX 76177.

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