Slow Food Fast

The International Journal of Obesity has just released a short article by Janet Tomiyama (UCLA) and Jeffrey Hunger (UC-Santa Barbara) et al–a team of psychologists. They analyzed NHANES data from 2005-2012 for about 75,000 individuals, and concluded that BMI status doesn’t correlate well with six concrete markers of cardiovascular and metabolic health–blood pressure, blood triglycerides and cholesterol, blood glucose, insulin resistance, and C-reactive protein. Extrapolating a bit from the NHANES study participant numbers, they conclude that millions of Americans–54 million–have been misclassified as unhealthy due solely to their BMI numbers.

According to their analysis, 47% of the overweight people in the study had healthy status (0-1 of 6 markers) other than their weight. About 30% of obese and even 16% of morbidly obese people had healthy status according to their protocol, whereas about 30% of those in the healthy BMI range had more than one actual cardiovascular or metabolic disease marker that would be ignored if only BMI is considered.

Is this really the death-knell for public concern over weight? Should it be?

Here’s how the UCLA press release puts it (with my emphases in italics):

But a new study led by UCLA psychologists has found that using BMI to gauge health incorrectly labels more than 54 million Americans as “unhealthy,” even though they are not.  […]

“Many people see obesity as a death sentence,” said A. Janet Tomiyama, an assistant professor of psychology in the UCLA College and the study’s lead author. “But the data show there are tens of millions of people who are overweight and obese and are perfectly healthy.”

Incorrectly labels? Perfectly healthy?

The definition for “healthy” used in this study is 0 to 1 known risk factor for CVD and diabetes. But clinically, one risk factor is often enough to be of acute concern, especially if it’s untreated high blood pressure or blood glucose. Those generally need treatment sooner rather than later.

Furthermore, the study as posted on Hunger’s web page excludes obesity and overweight a priori from that count of risk factors for CVD and diabetes. I don’t know the absolute latest research consensus, other than what was in the Dietary Guidelines for Americans Advisory Committee’s report last February, but my general understanding is that weight does show some statistically independent influence on CVD at least. That picture may be changing as we learn more about its interactions with other risk factors, but if it’s still valid, weight should have been counted as one of the existing “known risk factors” along with the other markers and that would have skewed Tomiyama and Hunger’s analysis considerably.

Even without those considerations, the different weight groups classified by BMI cutpoints do in fact show a significant increase in health risk from one category to the next. Turn Hunger and Tomiyama’s percentages around and you see that 70% of people in the 18.5-24.9 healthy BMI range have 0-1 risk marker other than weight; 53% in the 24.9-29.9 overweight range have more than 1 marker, 70% in the 30-35 range have more than 1 marker, and 84% in the 35 and over BMI range have more than one marker other than weight.

Plot those crude percentages and you’ll see a very sharp rise in risk incidence between the healthy and overweight categories, a reversal of fortune from “most people healthy” to “more than half at risk,” with further solidification of “most people at risk” as you venture further into obese and morbidly obese. There’s really no debating that trend, even given the narrow way this team has defined “healthy.” To say nothing of “perfectly healthy.”

Researchers in biomedicine (i.e., physical as opposed to psychological medicine) have recently reexamined whether the current BMI cutpoints defining healthy, overweight, obese and morbidly obese are in the right places to describe most people’s 10-year risk of overt CVD events (heart attacks and stroke), diabetes, or all-causes mortality, or whether BMI is just a continuous gradient of increased risk without definable cutpoints. At last count, the conclusion was that the current statistical best-fit cutpoints are pretty much correct, even though the data for individuals have a pretty big spread (and that each BMI step or number still has incrementally higher risk than the one below).

The upshot: BMI categories are still a pretty good marker of the overall health status of Americans when you’re talking about trends. Crude, yes. Exceptions for athletes with much more muscle than fat, yes. But the numbers are still strongly in favor of using BMI as a general warning flag to check for more specific cardiovascular and metabolic disease markers in individuals.

It’s very odd to see a paper like this coming from a team of behavioral psychologists, which Tomiyama and Hunger are. They’re at least nominally outside their field here, doing a statistical analysis on physical health data, and the paper’s methodology and definitions (along with some of their position statements in the American Journal of Public Health and elsewhere) show a specific agenda toward deconsecrating BMI and downplaying overweight and Continue reading →

Filed under: Diabetes, Food Politics, nutrition | Tagged: BMI, diabetes, health, health insurance, nutrition, obesity, public policy, research ethics | Comments Off on BMI criticized again…by psychologists?