Surprisingly, the BMI, or body mass index, was created back in the 1830’s by Adolphe Quetelet, a Belgian mathematician, astronomer and statistician, who developed a passionate interest in probability calculus that he applied to study human physical characteristics and social aptitudes. Disregarding growth spurts after birth and during puberty, Quetelet concluded that “weight increases as the square of height.” Known as the Quetelet Index until 1972, when it was termed Body Mass Index by Ansel Keys, BMI is the standard metric used to determine whether a person is under weight, normal weight, overweight or obese. The measure is revealed by dividing weight in kilograms by height in meters squared. As well, BMI calculators can be easily found online.
- Underweight: Below 18.5
- Proper weight: Between 18.5 and 25
- Overweight: Between 25 and 30
- Obese: Above 30
Well over a century later, BMI is still utilized as a measure of health, although it expresses the relationship between height and weight as a single number regardless of frame size and musculature. Proponents of the use of the BMI say that it remains relevant to an individual’s disease and mortality risk. Generally, those with excess weight are at a higher risk of developing a range of chronic conditions, including diabetes, arthritis, liver disease, sleep apnea, hypertension and high cholesterol, as well as breast, colon and prostate cancers. Independent of disease risk, those with high BMIs often report feeling better physically and psychologically with weight reduction.
Although it’s a useful starting point for the realization that disease risk rises along with weight, BMI, as a single measure, has its limitations. A recent study published in the International Journal of Obesity, examined cardiometabolic health misclassifications given standard BMI categories. Utilizing data such as blood pressure, triglyceride, cholesterol, glucose, insulin resistance and C-reactive protein, a marker of inflammation, the researchers found that nearly half of those considered overweight by BMI had a healthy cardiometabolic profile, including normal blood pressure, cholesterol and blood sugar. They also found that 30 percent of individuals with normal BMI measures had an unhealthy cardiometabolic profile.
While it remains a good idea to know your BMI number, it’s also important to recognize that it is simply a measure of size, and not a measure of health that indicates the absence or presence of disease. Indeed, there are those who have a high or low BMI who are healthy, as well as those with a normal BMI who are unhealthy. When relying solely on the one size fits all BMI measurement as the main indicator of health, more than 75 million adults may be mislabeled as cardiometabolically healthy or unhealthy. In fact, a person with a normal BMI who smokes and has a family history of cardiovascular disease is likely to have a higher risk of early cardiovascular death than someone who has a high BMI but is physically fit and a non-smoker.
BMI is widely used because it’s an easy and simple way to provide a reasonable measure of body fat. It does not consider the location of fat within the body and fails to account for differences in race, gender, age, height loss in older persons, or muscle weight in athletic individuals. While groups of researchers continue to debate the science of weight and poor health, some studies suggest that carrying a small amount of extra weight can improve survival of chronic disease. Just as a low BMI can indicate an illness, a recent UCLA study concluded that tens of millions of people who had overweight and obese BMI scores were in fact perfectly healthy. For those who follow a wholesome lifestyle and consume a nourishing diet, exercise, prioritize sleep and maintain healthy blood pressure, cholesterol and glucose levels, an extra few pounds may not be so unhealthy after all.
Adolphe Quetelet (179-1874)—the average man and indices of obesity. https://www.ncbi.nlm.nih.gov/pubmed/17890752
Misclassification of cardiometabolic health when using body mass index categories in NHANES 2005-2012. https://www.nature.com/articles/ijo201617
How useful is the body mass index (BMI)? https://www.health.harvard.edu/blog/how-useful-is-the-body-mass-index-bmi-201603309339
BMI Not a Good Measure of Healthy Body Weight, Researchers Argue. https://www.livescience.com/39097-bmi-not-accurate-health-measure.html