Because muscle is more dense than fat, bodybuilders can be categorized as obese.Abhishek Chinnappa / Reuters

Have you ever stepped on a bathroom scale and thought, This must be off. I’ve been blasting my core, and sleeping, and eating perfectly. Why am I not losing weight? I’m getting rid of this scale.

So you throw the scale in the trash? But then you get it out, because it was a gift? (Who gives a person a scale?)

That sort of sequence—so familiar—could be the result of the common misconception that body weight is the fundamental, ineffable metric of health. There are industries built around the idea, billboards and books and potions sold to advance the cause: Losing weight means we’re getting healthier, and gaining means the opposite.

Of course the total mass of our bodies isn’t meaningless, but it can be misleading, especially when taken as the central idea of fitness. A body of research suggests that a cultural obsession with bathrooms scales and “weight-loss” programs as the cornerstones of health could have us missing the point. In terms of health and longevity, the more important measurement is body composition—how much fat (adipose tissue) we have, and how much lean muscle.

To that end, a group of researchers this month is calling for everyone (doctors, journalists, everyone) to stop using the term “overweight.” We should all stop focusing on body weight and stop wantonly weighing ourselves. The advocating scientists, from the University of Auckland and elsewhere, wrote an exhaustive case in the journal Frontiers in Public Health, culminating with a call for replacing the term “overweight” with “overfat.”

I know, I know. That’s what I thought, too.

But then I tracked down one of the authors, Phil Maffetone, a recently retired primary-care clinician. He agreed that no term is perfect. But he’s convinced that overweight is more imperfect. In his former practice, he recalls, some patients would bring in spreadsheets of their daily bathroom-scale weights—hyperanalyzing every minor fluctuation and developing odd beliefs and superstitions about what caused weight loss, when in fact the changes in the body’s composition of water, fat, and muscle were all at play.

Obsession of that sort is only more problematic when the metric itself is flawed. The total weight of a person is a crude estimation of metabolic health, yet weight is the single most pervasive data point that most people—and their doctors—use in assessing and guiding health. The term “obesity” is currently defined by body mass index (BMI), a ratio of height and weight. “Overweight” is greater than 24, and “obesity” is greater than 29.

The scientific community has long known and accepted that BMI is imperfect. For example, because muscle is more dense than fat, bodybuilders can be categorized as obese. The more insidious problem is that people with lower BMIs, of “normal” body weight, may not be as healthy as the number suggests. These scenarios taken together have led the CDC to warn that while BMI “can be an indicator of high body fatness,” the measurement “is not diagnostic of the body fatness or health of an individual.”

Yet the world of consumer health and fitness is oriented around body weight. Almost all research about preventing cardiometabolic disease is predicated on BMI. When you hear, for example, that 66 percent of Americans (and around 40 percent of the world’s adults) are “obese or overweight”—statistics floating around news media and medical journals for years—that may be confusing the problem.

And Maffetone and colleagues see this as anything but a simple semantic quibble. They argue that people exposed to the term overfat versus overweight stand to make better-informed choices and set more meaningful health goals, because the term more accurately describes the pathology at play. Using BMI as the main indicator of obesity, meanwhile, “poses serious challenges to the accurate diagnosis, prevention, and treatment of obesity-related diseases.”

BMI might even underestimate the current scope of metabolic disease in the world. The researchers estimate that American rates of overfat may be as high as 76 percent––though by their own clear admission, the numbers are a preliminary, very rough estimate. Different techniques for measuring body fat tend to yield different results, and relatively few people have had it done by a reliable technique. Because of that, it’s also unclear where to draw a line between overfat and “normal” (and underfat). Thresholds will vary from population to population. The best example is that females have significantly more body fat than males but live longer, on average.

Still, just because BMI is easier to measure than body composition doesn’t mean it should be taken as sufficient. The most comprehensive U.S. data on body fat percentages comes from the National Health and Nutrition Examination Surveys (NHANES) and is based on dual-energy X-ray absorptiometry (DXA) scans. Based on that, U.S. men and women average 28 and 40 percent body fat respectively. And Americans with low BMIs tend to have more body fat that people with similar BMIs in other countries.

The Columbia University nutrition research associate Marie-Pierre St-Onge called these numbers “disconcerting” at the time of their publication, writing that “the notion that Americans may be over-fat warrants attention.” But she also cautioned that we don’t know exactly what percentages constitute what degrees of risk, so it’s difficult to give patients or doctors a concrete goal.

Of course, even if there were a clear, concrete goal, most people don’t own X-ray machines to measure our fat. And even if we did, it would be far from advisable to radiate ourselves daily, even weekly. For now, Maffetone thinks that people who are insistent on quantifying their bodies would simply be better off measuring their waist circumference than their total body weight. As he put it, replace the scale with a tape measure.

“And do it monthly––not daily, monthly,” he insists, again warning against obsession and concerns over day-to-day fluctuations.

Waist circumference does tend to be a meaningful indicator of health (though also, by itself, imperfect) because “central obesity” is the most dangerous sort. Adipose tissue that accumulates in the abdomen (not necessarily a “gut” or “love handles,” but deeper around the internal organs) is the type most strongly linked to serious disease. Adipose in the subcutaneous tissue, meanwhile, seems to be less dangerous. (This type accounts for much of the differences in male-female average body-fat percentages; while females have more overall body fat, males are more likely to carry pernicious stockpiles deep in their abdomens.)

Amid so many distinctions, a move toward more precisely characterizing the metabolic underpinnings of the leading causes of death seems worth considering.  A simple move away from scales and thoughtless usage of “overweight” could begin to more accurately frame the fundamental health problem of the era; to eliminate some undue concern among heavier people, and complacency among lighter ones.

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