What I learned about BMI
What I learned about BMI
Remember that time 29 million Americans went to bed with normal, healthy bodies, then woke up the next day and were "fat."
Everyone tells writers not to read the comments, and I tell all my sources not to read the comments, but here's a secret: We all read the comments. I've been reading the hundreds rolling in on my new New York Times Magazine feature, which was published online last week as “When You're Told You're Too Fat To Get Pregnant” and appeared in Sunday's issue of the magazine under the more understated “Hard to Conceive.”
Most of the comments on my Instagram and many on the piece itself are from women who, like Gina, Chelsea and Stephanie, have been turned down (often repeatedly) for fertility treatments on the basis of their Body Mass Index scores. Many other comments, especially on the NYT's Facebook page, are from people who think these women just don't want to face hard facts. If they have a high BMI, they must be unhealthy and unhealthy people can't have babies...or so their logic seems to go.
Except here's what I learned about BMI while reporting this piece: It's a pretty terrible metric for health. To be fair, that’s because it was never designed for this purpose. BMI is calculated by dividing a person’s weight in kilograms by the square of his or her height in meters. A Flemish astronomer and statistician named Lambert Adolph Jacques Quetelet developed the formula in 1835 as a way to determine the characteristics of an “average man.” Quetelet intended to measure only size, not health or even fatness, for that matter. As a result, BMI is a rather crude measure of body fat because it doesn’t consider gender, age or muscle mass, all of which factor into body composition. This is why many professional athletes have high BMIs when they're all muscle. And why research shows that folks who fall into the "overweight" range of the index are often healthier than folks in the "normal weight" range...because it's not measuring health.
But the World Health Organization adopted the BMI scale as its official classification of body weight for height in 1995, and it has since become medicine’s standard metric for measuring and categorizing patients by weight. A BMI below 18.5 is considered “underweight;” between 18.5 and 24.9 “normal,” 25 to 29.9 “overweight.” A BMI of 30 or above is classified as “obese,” the term still used by doctors, researchers and the media, although surveys of larger patients show that many now consider it derogatory. And to many, many doctors practicing across all specialties today, "obese" is synonymous with "unhealthy."
My big takeaway from reporting out how weight impacts a woman's fertility and prenatal health is that the relationship is far more complex than we think. High body weights are associated with some increased risks. They're also associated with many perfectly healthy outcomes. And that may be because so much of the science done on weight, and the medicine being practiced, rely on using BMI to define health.
As I wrote in Chapter 6 of my book: While researching her dissertation on the relationship between health and weight in the late 1990s, Linda Bacon, PhD, now an associate nutritionist at the University of California at Davis, was shocked to discover a large swath of research suggesting that the Body Mass Index, the system of tracking weight used by everyone from researchers to insurance companies, was deeply flawed. “Every study I found suggested that the BMI cut-off points for overweight and obese should actually be raised; that we were putting too many people in those categories when their weight didn’t actually correlate to much in the way of health problems,” she says. Instead, in June 1998, the National Institute of Health’s Obesity Task Force lowered all of the cut-off points. “Just like that, 29 million Americans who had gone to bed with normal, healthy bodies, woke up the next day and were fat,” Bacon explains. “The task force had looked at all of the same evidence as me and essentially thrown out the data.” Bacon draws a line between that decision and the subsequent marketing of two weight loss drugs by major pharmaceutical companies. “If you make more fat people, you have a bigger market.”
But one thing I struggled to understand when reporting this new piece was why doctors would turn away fat women, who, after all, represent paying customers as well as patients in need. It felt like the opposite of Bacon's contention that we created the obesity epidemic to sell diet pills. Then I learned about a popular marketing tool known within the fertility industry as a “shared-risk program” because it’s designed to reduce the financial risk borne by both patients and doctors. Clinics that offer such a program give patients a flat rate for three or four cycles of IVF. When patients get pregnant in the first cycle, clinic make a lot of money. If not, they have to reimburse patients for the cycles that don't work. "But these programs are money makers because they carefully select patients," one doctor told me. Clinics have a strong incentive to choose only the patients who seem likely to respond in the first cycle, which means that women who have a high BMI and might take longer to conceive are seen as financially risky — and often excluded, as are older women or women who already have a history of failed IVF attempts.
After I learned that, I saw that doctors’ refusal to serve heavier women might not have much to do with health at all.
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Inside story: Readers of the print edition were privy to a bit more behind-the-scenes detail via the Contributors page: During my reporting, one doctor asked about my weight, implying they shouldn't talk to any fat reporters about this. They played it off as a joke.
On the small screen: The Times story was also featured on Good Morning America! Watch here.
On the blog: Am newly OBSESSED with this new at-home yoga program by Jessamyn Stanley. Read all about it here.
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You're reading Burnt Toast, Virginia Sole-Smith's monthly newsletter. Virginia is a feminist writer, co-host of the Comfort Food Podcast, and author of The Eating Instinct. Comments? Questions? Email Virginia. If a friend forwarded this to you and you want to subscribe, sign up here.