Why The Body Mass Index Scale Is Unreliable


The Body Mass Index Scale was created in the 1830’s as a way for Belgian scientists to easily study human growth. However, it was never meant to be a way to measure individual body weight. It was just a way to easily group averages of people into categories and follow their weight changes. Despite this fact, it was adopted to be a simple and easy way for doctors and people at home to have a quick answer to figuring our whether they were fat or not.

The way to find out your body mass index is by using the mathematical formula (kg)/height (m)^2 = 703*weight (lb)/height (in)^2. Using this formula and plugging in all of the numbers that apply to a person can be used the end number used on the scale itself. The scale itself is what determines how healthy a person is. The scale says that 18.5 and below is too normal weight, 18.6 through 24.9 is normal weight, 25 through 29.9 is overweight, and 30 or greater is obese. (National Heart, Blood, and Lung Institute) Those numbers have been changed before however, and are not permanent.

The BMI scale is also inconsistent. The definition of obese is thrown around and where a person stands on the BMI scale can be changed from healthy to obese fairly quickly. “In July 1998, the National Institutes of Health changed what it means to be overweight . . . so suddenly about 29 million Americans who had been considered normal became overweight even though they hadn’t gained an ounce.” (Brody, 2014) This can leave people confused and unsure about where they really stand on the obesity scale. This inconsistency creates even more inaccuracies in the BMI scale because the obesity cutoff is not obsolete.

Adolphe Quetelet created the Body Mass Index Scale, but it was not for the reason that it is used today. Quetelet is considered to be the founder of the social sciences. From an early age he was seen as a math genius, but he decided to dedicate his life to humanities instead. “His concern was defining the characteristics of ‘normal man’” (Eknoyan, 2007). In his studies on this subject, he wanted to experiment with what made a normal man, and that included what the average normal weight was. Thus, the BMI scale was invented.

In the body, there are many different types of fats. The BMI scale does not take separate fat from the rest of the body. Even if the result one got was overweight, they could actually be perfect health. A major area that the BMI scale just lumps together into one calculation is the abdominal fat. This makes for an inaccurate measurement because some of these fats may not factor into the scale or factor in too much, leaving the person at risk for diseases they did not know about. There are different types of abdominal fats- some good, some bad. The two main types are subcutaneous fat and visceral fat.

The kind of abdominal fat that is okay for one to have is subcutaneous fat. Subcutaneous fat lies directly underneath the skin on the abdominal area. Though it does contain fatty tissues, it also contains things that are vital to living. It has blood vessels to supply the skin with oxygen and nerves that can send signals of pain. This fat is also a cushion, so when trauma happens to that area, it can be absorbed slightly by it. Because subcutaneous fat stores energy, it is also easy to burn off by exercise, leaving it fairly harmless to the body.

Visceral fats are what are really harmful the body. “Visceral obesity was linked to over activity of the body’s stress response mechanisms, which raise blood pressure, blood sugar levels, and cardiac risk.” (Harvard Education, 2005). The reason visceral fats do this is because they encase important arteries such as the liver, pancreas, and intestines. A high amount of visceral fats can lead to high levels of glucose intolerance. Visceral fats link to many diseases such as type 2 diabetes, heart disease, breast cancer, Alzheimer disease, and colorectal cancer.

The best way to find out if one has an abundance of visceral fats is by getting a computed tomography or magnetic resonance imaging. These are both also known as CT scans and CT scans. However, this solution is not very obtainable because it is expensive and is reserved for more serious threats. An easier method that is available at home is the waist-to-hip ratio. It is another mathematical formula, but it is specifically created for abdominal fats, making it much more accurate than using the BMI scale.

An Oxford mathematician, Nick Trefethen, believes that the Body Mass Index scale is flawed as well. He says that the system is flawed because it does not account for people who have different body types. In a letter to The Economist Trefethen says that “No single number can be right, and indeed, the extreme reliance of today’s medical and insurance establishments on a simple formula worries me a great deal.” (Trefethen, 2013) Though he says no number is correct for very person, he still gives a formula that would more accurately represent a wider range of body types, especially taller people. His formula is 1.3*weight (kg)/height (m)^2.5 = 5734*weight (lb)/height (in)^2.5.

Nick Trefethen says that even though the small change might seem insignificant, it would affect millions of people’s lives. Anyone that is around five feet would get a point added to his or her number and anyone that is around six feet would get a point subtracted. This takes out the problem of natural weight as the body grows taller not being accounted for. Just the change of one digit could determine whether a person is obese or just overweight. As it currently stands, the BMI scale leans heavily in favor of shorter people because it makes them seem skinnier than they might actually be. The percentage of people affected by this change would be much higher than the people affected by their muscle being grouped in with their fat and making a large difference to their scale number. That percent of people is just 1.8% (Trefethen, 2013). Thought Catalog Logo Mark

Works Cited:

Brody, J. (2014, April 21). Body Mass Index a Flawed Measure of Obesity.

Eknoyan, G. (2007, May 24). Adolphe Quetelet (1796–1874)—the Average Man and Indices of Obesity. Houston, TX, USA.

Harvard Education. (2005, September 5). Abdominal Obesity and Your Health. Cambridge, MA, USA.

National Heart, Blood, and Lung Institute. (n.d.). Calculate Your Body Mass Index. Bethesda, MD, USA.

Trefethen, N. (2013, January 5). BMI (Body Mass Index). Oxford, Wellington, UK.

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