We’re still living large. Very large. According to the latest statistics from the Centers for Disease Control, 39.8 percent of adult Americans and 18.5 percent of American youths were obese in 2016. While these rates aren’t much worse than those from a couple of years ago, they’re not any better either. Obesity, in short, is a slow motion crisis that is stripping health and ultimately longevity from almost half the population.
Or is it? Obesity isn’t strictly a matter of public health. It is also a social and political issue, nearly as fraught with conflict as race and class. And for some time, a “fat but healthy” meme has been building, with proponents maintaining weight alone doesn’t determine fitness and vitality and that public preoccupation with obesity is a symptom of a fat-phobic culture.
Recent studies indicate that both sides may have a point: Yes, for most people, obesity is a deleterious condition, leading to hypertension, elevated fasting glucose (pre-diabetes), diabetes, elevated triglycerides (i.e., fat in the blood), low HDL cholesterol (the “good” cholesterol), and increased cancer risk. But for a significant minority of obese people, roughly 30 percent, such conditions don’t apply. They are, in medical parlance, within normal limits.
Such people, says UC Berkeley School of Public Health assistant professor of epidemiology Patrick Bradshaw, have a normal metabolic profile, an indication that metabolic stability is a better indicator of true health than weight alone. And that points to a need for a more nuanced set of metrics when considering the status of the obese and overweight. Currently, most clinicians use Body Mass Index (BMI) to gauge health risk. The BMI is derived by dividing body mass by the square of the body height; a BMI of 24 to 29 indicates excessive weight, and anyone with a BMI 30 or above is considered obese.
“The problem is that BMI doesn’t identify people with metabolic derangement,” says Bradshaw. “It’s convenient but it’s a blunt tool. We need a more refined approach that accounts for both body size and metabolic status.”
Fat does count, but it’s not just about the amount, observes Bradshaw: it also matters where it is.
“Where you carry adipose issue is important,” says Bradshaw. “It appears to be less of a health risk if it’s under the skin and over the hips rather than around the organs and centrally located in the abdomen. Visceral fat, the kind that’s stored around the organs produces chemicals that are specifically related to inflammation and insulin resistance.”
If anything, BMI should be viewed as a starting point in assessing weight-associated health risk, says Bradshaw. Full metabolic tests are essential, including blood pressure and blood panels that include triglycerides, HDL, and LDL (the “bad” cholesterol) assays, and perhaps other tests as individual cases warrant. In other words, physicians need to resist the temptation to lump all overweight and obese people into broad categories.
Further, it shouldn’t necessarily be assumed that dramatic weight loss will prove a panacea for metabolic disorders. Bradshaw cites a study involving a group of “metabolically healthy” obese women who underwent regimens that resulted in significant weight loss; generally, their metabolic profiles worsened.
“It’s likely that they lost muscle mass, because when you lose fat you also tend to lose muscle,” Bradshaw says, “and muscle seems to provide some measure of metabolic protection. That’s another reason that BMI is iffy: it doesn’t account for muscle mass. Ideally, we’d like to find some way to lose fat without losing muscle.”
Loss of muscle mass is also a concomitant of age, and likely is linked to the rising fasting glucose levels that typically afflict the elderly, says Bradshaw.
But metabolic anomalies don’t only bedevil the obese and overweight, adds Bradshaw. The seminal 2008 study in the Journal of the American Medical Association by Rachel Wildman that found 30 percent of overweight people are metabolically healthy also determined that 25 percent of people within normal weight ranges were metabolically abnormal.
“That said, it’s very important that people don’t misconstrue the significance of these findings,” Bradshaw says. “We don’t want to give the public any excuse to forego weight loss. Weight matters. But so does metabolic health. The important takeaway is that metabolic health needs to be monitored. Also, we know that the success rate for long-term weight loss is extremely low, and that tends to discourage people from even trying. So instead of going for massive weight loss, it may make more sense to focus on metabolic health by losing some weight, exercising regularly and eating healthy foods.”