You’ve likely heard the term “BMI” before, or seen “BMI calculators” online, but you may have struggled to understand what it means or how useful it really is. Here’s what it’s all about.
“BMI stands for body mass index, and is just one of many types of calculations that are helpful in providing a quick glimpse into one’s health, based on weight and height,” says Hannah Daugherty, NASM- and ACE-certified personal trainer and health coach.
“By dividing weight in kilograms by height in metres squared, the given number then falls into a category (underweight, normal, overweight or levels of obesity). While an initial glance at BMI calculations may make it seem like an excellent way to determine if someone is at a healthy weight, it does have some flaws,” she says. “Body composition is different between men and women, yet the BMI calculation for both genders is the same; this means that regardless of how much muscle or fat someone has, the calculation can’t determine between the two – just the end result of pounds on the scale. BMI also doesn’t take into consideration any other lifestyle factors, such as diet, sleep quality, exercise habits or even medications, so it doesn’t paint a full picture of one’s health.”
Registered nurse and specialist at Health Canal Krista Elkins says BMI is the current standard to determine if a person is at a healthy weight.
“BMI determines a person’s body fat, and if it is under or above what is considered ‘normal,’ it can be a good indicator of whether or not a person is at a higher risk for poor health. It can help a doctor determine if a person is at a higher risk for developing diseases such as heart disease or diabetes,” she says.
“To some, BMI is considered outdated and oversimplified, as there are many variables to consider when determining a person’s health, such as diet, exercise, and genetics. It is current best practice to use how much fat a person carries at their waistline as one indicator of their risk for disease.”
“Like any indirect measure, the BMI calculation has disadvantages when used as a marker of health for an individual,” explains Emma Laing, PhD, RDN, director of dietetics at the University of Georgia and a spokesperson for the Academy of Nutrition and Dietetics.
“For example,” Laing says, “BMI cannot accurately estimate the amount of fat or muscle mass that a person has, nor is it reliable among very tall or very short people. Also, it does not take into consideration ethnic variations that may impact body composition or size.”
Laing adds, “There is no such thing as a one-size-fits-all approach to health. The BMI is a proxy that is often used to assess someone’s general health, but there are other measures that can tell us more useful information. For example, fluctuations in weight and therefore BMI can happen due to changes in muscle mass, hormonal status, and hydration. Other factors like strength, endurance, blood pressure, blood sugar, and cholesterol levels might change in response to your eating and movement patterns – even if BMI doesn’t. Paying attention to these objective markers, as well as your energy levels, sleep patterns and emotions are important for making decisions about your health.
Hyper-focusing on your BMI can often lead to feelings of shame, guilt, and anxiety, and any one of these can have a profound impact on a person’s life. Despite the personal responsibility that is typically expected of people to control their body size, the BMI is not something many people can control, at least long-term.”