Body Mass Index (BMI)

Body mass index (BMI), refers to the measurement of a person using weight in relation to height. Despite its limitations, many studies have found correlations of correct BMI assessments with body fat rate, making it a reliable method. It is also useful to help assess the health risks of people who suffer from eating disorders such as anorexia nervosa and bulimia. It is not, however, a diagnostic tool. Improvements have been done on the BMI calculations through the decades. There are several ways to calculate BMI, and the most common relies on the mathematical formula weight(kg)/height(m2). In general, the higher the BMI number, the more fat the body has. A high BMI may put the person at risk for chronic diseases such as heart disease and diabetes.

Brief History

The BMI measurement is also known as the Quetelet Index after its French inventor, Adolphe Quetelet, who designed it in the mid-nineteenth century. It became known as BMI and popularized in the early 1970s, after a study published by Ancel Benjamin Keys, the American scientist and nutritionist who invented the K-rations for US soldiers during World War II. Keys also identified the Mediterranean diet as a healthful alternative to the typical American diet. Based on the traditional diets of southern Europe, the Mediterranean diet has been linked to the health and longevity of the populations who consume it.

Since its invention in the 1800s and its revival in the 1970s, several organizations, such as the World Health Organization (WHO) and the US Centers for Disease Control (CDC), among others, have worked to consistently improve and modify the BMI measurement system. In general, BMI is an index to measure fatness or fat levels, which applies to adults preferably over 20 years of age. It can be also be used to measure weight levels in children and adolescents, but weight levels fluctuate so often through age and sex among children, that the CDC created weight charts for underage people based on percentiles according to sex and age.

The CDC has also added modifications to the BMI, in order to better assess the fat levels of some populations, such as the elderly and athletes. The basic BMI categories are as follow:

Underweight = 18.5 and below

Normal weight = 18.5 to 24.9

Overweight = 25 to 29.9

Obesity −30 or greater.

BMI is considered important because of the health risks associated with being overweight. According to some medical studies, excessive body weight—especially after middle age—is associated with myriad chronic diseases, health problems, and even death. For most of the adult population, BMI measurements are a good tool to estimate the healthy weight range of individuals. Therefore, medical personnel often use BMI to determine if a patient is overweight and often try to make some adjustments related to age and sex; the elderly, for example, may report a lower BMI due to muscle loss yet be overweight in reality.

Overview

Even though it is considered a reliable fat rate measurement and health risk predictor, experts warn against considering BMI estimates as a diagnosis. An in-depth examination aimed at determining a person’s level of overweight and health risks needs to include other elements, such as measuring body fat by way of skinfold thickness using calipers, waist measurements, family medical history, ethnicity, occupation, and myriad other factors that should be taken into account when determining an individual’s ideal weight and health risks. These should be performed by medical personnel or those highly trained in performing health screenings.

Despite its challenges and limitations, according to the CDC, paying attention to BMI is important because people who are extremely overweight or obese are at increased risk for many diseases and harmful health conditions, including hypertension, or high blood pressure, high low-density lipoprotein (LDL) cholesterol, type 2 diabetes, strokes, osteoarthritis, some cancers, some chronic conditions, and even mental illness, such as anxiety and depression, among others. The CDC also recommends combining BMI calculations with other measurements when available, such as underwater weighing, bioelectrical impedance, dual energy x-ray absorptiometry, and isotope dilution. However, since these require trained personnel and are not always available, BMI remains a simple and inexpensive way of calculating healthy weight levels in individuals.

Although BMI is a common measure, it is also the subject of several criticisms. Among the most common critiques is that BMI is too general and even inaccurate; it does not, for instance, take into account that different populations have different degrees of fatness due to genetics or natural body shapes or proportions. It also cannot distinguish between healthy and unhealthy types of body mass. Fat gets distributed differently among different groups; for example, differences exist between Asian and some Pacific Asian groups. Moreover, some athletes may be perfectly healthy and not overweight, yet report a higher BMI due to increased muscle mass.

Therefore, BMI interpretations should take into account several biological and societal factors. Some experts have proposed that the definitions for overweight in the WHO classification be amended to include these variants. In response, the WHO added cut-off points for observed health risks among different populations, which allows for better international comparisons.

The importance of using BMI has become clearer in the last decades, as the number of health studies grows which link body weight, health risks, and longevity. For example, close to 80 percent of individuals diagnosed with type 2 diabetes are also overweight or obese. Other chronic diseases that correlate with being overweight are hypertension, high cholesterol, heart disease and as a consequence of these, kidney damage, stroke, liver and gallbladder disease, as well as several types of cancer, among others. In some of these cases, scientists have not yet found the reason for these correlations. However, it is believed that excess weight serves as a catalyst for changes in cell structures and functions, and in other important bodily functions such as heart pumping and blood circulation, due to the overwork the organism undergoes because of the increased body mass caused by obesity.

Bibliography

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Bacon, Linda, and Lucy Aphramor. Body Respect: What Conventional Health Books Get Wrong, Leave Out, and Just Plain Fail to Understand about Weight. Benbella, 2014.

"Body Mass Index (BMI)." Cleveland Clinic, 9 May 2022, my.clevelandclinic.org/health/articles/9464-body-mass-index-bmi. Accessed 1 Nov. 2024.

“BMI Classification.” Global Database on Body Mass Index, World Health Organization, www.assessmentpsychology.com/icbmi.htm. Accessed 1 Nov. 2024.

Brown, Harriet. Body of Truth: How Science, History and Culture Drive Our Obsession with Weight—And What We Can Do about It. De Capo, 2015.

Flegal, Katherine M., Brian K. Kit, Heather Orpana, and Barry I. Graubard. “Association of All-Cause Mortality with Overweight and Obesity Using Standard Body Mass Index Categories: A Systematic Review and Meta-analysis.” The Journal of the American Medical Association, vol. 309, no. 1, 2013, pp. 71–82.

Keys, Ancel, Flaminio Fidanza, Martti J. Karvonen, Noboru Kimura, and Henry L. Taylor. “Indices of Relative Weight and Obesity.” Journal of Chronic Diseases, vol. 25, no. 6/7, 1972, pp. 329–43.

Sook Hee, Yoon, et al. “Combined Effect of Body Mass Index and Body Size Perception on Metabolic Syndrome in South Korea: Results of the Fifth Korea National Health and Nutrition Examination Surveys (2010–2012).” BMC Public Health, vol. 15, no. 1, 2015, pp. 1–15. Academic Search Complete. Accessed 1 Nov. 2024.