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How much you weigh gets a lot of attention despite being one of the least telling measures of health.
On almost any trip to the doctor’s office, the first measurement is taken right there in the clinic hallway — on the scale. Others follow in the privacy of the exam room and lab, but that first one is prominent, prompt, and public. The nurse scribbles your weight on your chart like a grade, often before you even have a chance to say why you’re there.
There’s no doubt about it — in the world of healthcare, weight is given . . . a lot of weight.
But how important is that number really?
Media headlines and the medical establishment alike tend to conflate fatness with sickness. Alarms sound about the rising number of people who qualify as overweight or obese, and the presumed implications for public health.
Yet research suggests that the relationship between heaviness and disease is more complicated and less direct than we’ve been led to believe. In fact, the notion that weight is a reliable predictor of health and fitness appears to be simply incorrect.
Instead, what counts as a healthy body size is likely to be highly individual, and well-being is better gauged by measures not found on a scale, including good labs, stress levels, sleep, movement, and a positive relationship with food.
Indeed, a chart definition of health based on weight may cause more problems than it solves.
Public-health officials use body mass index (BMI) to classify people as underweight, normal weight, overweight, or obese, based on a simple equation — a person’s weight in kilograms divided by the square of their height in meters.
A BMI between 18.5 and 24.9 is considered “normal or healthy weight” for adult men and women, while a score of 25 to 29.9 is “overweight,” and anything over 30 is ruled “obese.”
But even the Centers for Disease Control and Prevention acknowledges that BMI alone is “not diagnostic of the body fatness or health of an individual.”
The BMI equation doesn’t differentiate between muscle and body fat, for starters, so a muscular athlete can easily have a BMI over 30. (According to the BMI scale, shown below, Dwayne “The Rock” Johnson qualifies as “obese.”)
And because the equation was developed using Western European bodies to determine averages, BMI has been shown to overestimate obesity in Black people; at the same BMI, Black people typically have less overall body fat than white people, according to research cited by the CDC.
What’s more, a 2013 study published in JAMA found no linear relationship between BMI and risk of premature death. Rather, researchers described a U-shaped curve, with the lowest risk of death for those in the “overweight” category (around 25 to 26 BMI).
People considered “mildly obese” had about the same risk of dying prematurely as those in the “normal” category. Death rates rose (slightly) at either end of the curve, for those considered underweight or obese.
Still, despite its limitations as a diagnostic tool, BMI is measured on almost any trip to the doctor’s office.
“It’s unfortunate that BMI has become a common measure of health,” says Dana Magee, RD, LD, a weight-inclusive nutrition coach in Annapolis, Md., noting that the index was originally intended for analysis at the population level, not to offer insight into an individual’s health. (It was introduced by Belgian mathematician Adolphe Quetelet in the 19th century as a way to gauge obesity rates across the general population.)
“Now every doctor’s-office printout mentions it, and it takes the focus off important things and puts it on something that doesn’t have a direct link to health,” says Magee.
Body-fat percentage may provide slightly more insight than BMI because it accounts for muscle and bone mass in its measurements. But according to Jennifer Campbell, MS, a nutrition and behavior-change coach based in British Columbia, it still fails to take into account that different kinds of fat — such as visceral abdominal fat versus subcutaneous fat throughout the body — may have different implications for health. Fat cells in the abdomen, for instance, can release molecules that contribute to systemic inflammation and insulin resistance, unlike more evenly distributed subcutaneous fat.
And measuring body-fat percentage still suggests that fat or body size in excess of what’s on a chart is automatically a health problem.
“All these different ways of measuring body size completely ignore emotional, mental, and social health,” notes Campbell.
So why does the medical establishment still rely on body-size measurements as critical indicators of someone’s overall health status?
“Weight is such an easy thing to measure,” says Sandra Aamodt, PhD, author of Why Diets Make Us Fat. “Most other more-indicative measures require blood tests or fasting first, so they’re much less convenient than weight. Weight is only a correlate of some of these more useful tests — and not a fantastic one at that — but it’s very easy to get.”
Yes! Strength and fitness are almost entirely independent of body size, and there are plenty of reasons to pursue them that have nothing to do with weight loss.
“Movement triggers tremendous changes in your musculoskeletal and cardiovascular systems and in the hormones and neurotransmitters involved in health, such as the all-important relaxation response,” write Bacon and coauthor Lucy Aphramor, PhD, RD, in Body Respect. They note that exercise helps to increase energy, improve sleep, enhance mood, and confer a sense of overall well-being.
A 2014 study in European Endocrinology showed that “obese” people who are at least moderately fit have a lower mortality risk than those who are “normal” weight but unfit. This means that fitness is a better predictor of health than weight — and the two do not necessarily go hand-in-hand.
The same researchers found that improving cardiorespiratory fitness plays a bigger role than weight loss in protecting individuals with type 2 diabetes from cardiovascular disease.
