Uses of Body-Mass Index in Health Care Called Into Question

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Uses of Body-Mass Index in Health Care Called Into Question

A growing number of doctors and other health experts are questioning the way a person’s body-mass index (BMI, a measure of body weight that takes height into account) is used to make medical decisions, as noted in a recent article at Kaiser Health News.

In the current health care system, BMI is a widespread measure used to designate a person’s body weight as falling in the categories of underweight, normal weight, overweight, obesity, and extreme obesity. While BMI undoubtedly is useful as a way to get doctors and patients to take a second look at a person’s body weight and what it could mean for health, there are potential problems with how BMI is currently used in many area of health care, the experts point out.

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For example, many health insurance plans will only pay for weight-loss drugs or bariatric (weight-loss) surgery if someone has a BMI above a certain threshold — such as 35 for bariatric surgery, or 30 for many weight-loss drugs. While it may be possible for a doctor to argue that someone’s overall health situation justifies the surgery or drug, getting approval can be an arduous process if someone’s BMI falls even just outside the approved range.

Even when someone starts out at a BMI that qualifies for insurance coverage of a weight-loss drug, their insurance company may no longer cover the drug once their BMI drops below the qualifying threshold — essentially taking the treatment away because it’s working. And without continuing to take the weight-loss drug, a person’s body weight can rise again.

The issues with BMI cutoffs

BMI cutoffs are a problem in general, critics say, because BMI carries limited value as a measurement. It doesn’t differentiate between fat and muscle, or between different types of fat — all of which can have a large effect on a person’s metabolic and overall health. As a result, people who are at a healthy body weight may have a BMI that categorizes them as overweight, while other people with an unhealthy level of body fat may be categorized as having a normal body weight.

Another area where BMI can be problematic is eating disorders, since it’s often used as a tool to screen people for them — not part of the diagnostic process, but as a way to prompt health acre providers to ask certain questions that may lead to a diagnosis. But some people with eating disorders — such as anorexia and bulimia — aren’t underweight, which means they might not get the attention and treatment they need.

Studies also suggest that BMI might underestimate or overestimate the health risks linked to excess body weight in certain racial or ethnic groups. Compared with other groups, there is evidence that people of Asian descent have a higher risk for diabetes at lower body weights. This evidence is so strong, in fact, that countries including Japan and China have set lower thresholds for overweight and obesity for people of Asian descent (the vast majority of their populations). At the same time, there is evidence that Black women tend to have fewer health problems at a BMI just above 30 — the official cutoff for obesity — than other groups.

Another problem with BMI, according to an article at MedPage Today by two eating disorders experts, is that it can lead to “unproductive weight-related conversations” between doctors and their patients that make patients feel ashamed or stigmatized — and less likely to follow their doctor’s advice about healthy behaviors. There is even some evidence that a fear of getting weighed keeps many people with overweight or obesity away from their doctor’s office, which is clearly not the intended effect of BMI measurements. The authors argue that if BMI were not already a common measurement in health care and you heard a sales pitch for why it should be used, that pitch would fall flat — there are better measurements of body composition, and BMI performs worse in older people and athletes. It’s only real advantage, they write, is that it’s cheap and easy to use.

A possible BMI alternative

But, in fact, many experts recommend an alternative to BMI that is arguably even cheaper and easier to use — waist size, which requires nothing more than a tape measure. That’s because excess body weight in your midsection — also known as abdominal obesity — is a much better indicator of poor metabolic health than excess weight in your legs or other areas. Meanwhile, there is ongoing research aimed at developing better measurement of health risks linked to excess body weight, which may take multiple factors into account — such as your weight, height, waist size, and race or ethnicity. But it will probably be a long time before any newly developed index gains widespread acceptance throughout the health care system.

Want to learn more about abdominal weight? Read “Eight Ways to Lose Belly Fat.”

Quinn Phillips

Quinn Phillips

Quinn Phillips on social media

A freelance health writer and editor based in Wisconsin, Phillips has a degree from Harvard University. He is a former Editorial Assistant for Diabetes Self-Management and has years of experience covering diabetes and related health conditions. Phillips writes on a variety of topics, but is especially interested in the intersection of health and public policy.

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