The Obesity Epidemic and the Body Mass Index (BMI)

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Obesity is increasing globally. One way to 'measure' obesity is by using the bdy mass index (BMI). This article discusses both the increase in obesity and the use of the BMI

Increasing Numbers

According to the World Health Organization, the increasing life expectancy could possibly be put on hold by the increasing occurrence of obesity. The data, acquired in 2005, indicate that around 1.6 billion people are overweight globally, of which about half a billion are obese.

Most cases of obesity are found in the Western world, but it is no longer limited geographically, as obesity is on the rise in other countries as well.

BMI (Body Mass Index)

A general tool for diagnosing obesity, is the body mass index (BMI). This is calculated in the following manner:

Bodyweight (in kg) / (Height in m)²

So, for example, somebody who is 1.78 m (or 5 foot 10 inches) tall and weighs 75 kg (a little over 165 pounds), has a BMI of 76 / 1.78² = 24.

A ‘normal’ BMI is considered to lie between 18.5 and 24.9. below 18.5, a person is ‘underweight’; between 25 and 30, a person is overweight; and above 30, a person is obese.

Yet it should be kept in mind that these boundaries are arbitrary. If your BMI goes from 24.5 to 25, that doesn’t mean you suddenly got less healthy. Or if you eat healthy and exercises regularly, but have a BMI of 27, that doesn’t mean you have to lose weight. The BMI does not take in account the nature of the tissue, so if you’re very muscular, or have very dense bones, you will have a relatively high BMI, without being overweight or unhealthy.

This is a common heard remark about the BMI as indicator of health. Nevertheless, it can serve as a guideline and help people understand their situation.

BMI and Life Expectancy

The connection between BMI and life expectancy has been extensively studied in hundreds of thousands of Europeans, Americans and Asians. The results all show that the correlation between BMI and life expectancy follow a U-shaped curve, meaning that people with a very low and very high BMI have the lowest life expectancy.The lowest point on the curve lies around a BMI of about 25, but the valley stretches from about 21 to 28.

So, BMI is a good indicator of your ‘weight status’ and health, but it is by no means perfect, as it does not take into account individual differences in body structure.

References

  • Olshansky, S.J.; Passaro, D.J.; Hershow, R.C.; Layden, J.; Carnes, B.A.; Brody, J.; Hayflick, L.; Butler, R.N.; Allison, D.B. & Ludwig, D.S. (2005). A Potential Decline in Life Expectancy in the United States in the 21st Century. New England Journal of Medicine. 235, pp. 1138 – 1145.
  • Peeters, A.; Barendregt, J.J.; Willekens, F.; Mackenbach, J.P.; Al Mamun, A. & Bonneux, L. (2003). Annals of Internal Medicine. 138(1), pp. 24 – 32.
  • World Health Organization, Obesity: http://www.who.int/topics/obesity/en/

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