Does a Low BMI Mean I’m Healthy?
Unfortunately, not necessarily
The infamous BMI scale is still the standard to determine whether a person is underweight, normal, overweight, or obese.
I’ve been subject to it at every annual physical. When my doctor saw that I was a “normal” BMI two years ago, she sent me off and basically told me to keep doing what I was doing. But I knew that my eating habits at the time were the worst that they had ever been! But since the BMI said that I was “normal,” I figured that meant I was healthy enough… Turns out the BMI should stand for bring more information, because having a low or normal BMI isn’t synonymous with healthy.
Low BMI is Good, Right?
Most people think that a low BMI is correlated with an active, healthy lifestyle and a high metabolic rate. Why else would the BMI say body fat percentage was so low? But researchers have found that this is not usually the case.
In the study, those with lower BMIs had lower food intakes AND lower activity. Their metabolic rates were higher, but not for a very “healthy” reason…they had elevated levels of their thyroid hormones.
Many reasons can affect why a BMI reading is not accurate. A BMI doesn’t take into account anything related to body composition, such as muscle, fat, or bone density.
It’s also possible to have a “normal” BMI while also having too much fat and too little muscle in the body. This is most commonly related to visceral fat. Visceral body fat is also known as ‘hidden’ fat because it’s fat stored deep inside the abdomen and around the organs. It should make up only one tenth of all fat stored in the body. The BMI isn’t able to take into account how much of this fat you really have, and even a “normal” BMI person could have too much visceral fat stores in comparison to muscle.
What’s a Better Way to Measure Health?
A simple method is the waist-to-height ratio, which is shown to be better than the BMI. This compares the waist circumference to height, so it takes your central fat into consideration. Researchers have also analyzed separate studies and found that the waist-to-height ratio was more accurate than BMI at predicting certain diseases. A simple index used that utilizes the waist to height circumference is the RFM, which is calculated by:
Men RFM = 64 — (20 x height/waist circumference)
Women RFM = 76 — (20 x height/waist circumference)
Skin fold thickness is also a measurement that is reliable, simple, and cheap. It measures the thickness of subcutaneous fat (or fat under the skin) at different sites in the body. A skinfold caliper is used to assess the skinfold thickness, and then a prediction of the total amount of body fat is made. One study particularly showed how skinfold thickness was a better predictor of body fat than the BMI.
If you want to be super accurate, then an interesting new method of fat composition that I came across is hydrostatic weighing, which is an underwater weighing technique. It measures both body density and composition.
To do hydrostatic weighing, you first weigh yourself on land. Then, you sit in the water on a chair that is on a scale. Next, you expel all the air from your lungs and stay still until the measurement for the underwater weight is taken.
Because muscle weighs more than fat, a person with more muscle will weigh more underwater. Those with more fat will be more buoyant underwater. Hydrostatic weighing tests are available at many fitness centers and local providers.
Conclusion
It’s time to seriously reconsider using the BMI as a standard for healthy. Although it is the go-to measurement for most healthcare providers, there are many measurements that are more accurate and can give you a better indication of your health!
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