Ozempic’s Big Test

Taken on its own, the number is astonishing. According to the CDC, as of August 2023, 40.3 percent of U.S. adults—some 100 million people—met the clinical definition for obesity. But this same estimate, which is based on National Health and Nutrition Examination Survey numbers gathered between 2021 and 2023, also seems remarkably low compared with prior readouts. For the first time in more than a decade, NHANES data hint that our obesity epidemic is no longer growing.

The new estimate is almost two percentage points lower than the government’s previous one, which covered the period from 2017 to 2020 and suggested that 41.9 percent of Americans had obesity. The apparent drop has set off a wave of optimism: A recent editorial in The Washington Post, for instance, celebrated the fact that “the obesity crisis might have plateaued or begun to ease,” and in the Financial Times, the data journalist John Burn-Murdoch used his own analysis of the NHANES data to argue that America is already several years beyond its point of peak obesity. Both outlets suggest that this apparent change in public fortune has resulted from the spread of powerful new drugs for treating diabetes and obesity: Ozempic, Mounjaro, and the rest.

The past few years have certainly brought dramatic changes—historic breakthroughs, even—to the treatment of weight-related chronic illness. GLP-1s seem to be effective at improving people’s health, and they’re clearly capable of causing major weight loss. According to a survey conducted by KFF at the end of April, 6 percent of all American adults are currently on these medications, and as supply shortages ease and drug prices come down, that proportion is likely to increase—by a lot. It only stands to reason that, at some point before too long, their effects will be apparent in our public-health statistics. But are they now, already? For all the expectations that are attached to the present age of GLP-1s, the past should be a source of caution. This is not the first time that obesity’s relentless spread has seemed to be abating, and it’s not the first time that such news has fit into a tidy narrative of progress in public health. And so far, at least, claims of peak obesity, like predictions of “peak oil,” have been prone to falling flat.

Not so long ago, the NHANES data appeared consistent with a different source of hope. Starting back in 2008, analyses began to show, first in children and then in adults, that obesity rates were leveling off. “Americans, at least as a group, may have reached their peak of obesity,” The New York Times asserted in 2010; two years later, NPR reported that “the nation’s obesity epidemic appears to have hit a plateau.”

Then, as now, experts had a convenient story to explain the numbers. Barack Obama’s administration was working to realize his campaign promise that the nation’s excess weight could be reduced, if not erased, by targeting what was by then described as America’s “toxic food environment.” Revised nutrition labels put a spotlight on “added sugars,” new rules for food assistance promoted eating fruits and vegetables, insurers were encouraged to set up wellness programs, and chain restaurants were required to post the caloric content of their meals.

For a time, this new approach—based less on treating individuals than fixing social policy—appeared to be effective. Food manufacturers committed to improving the formulations of their products. Americans stopped drinking so much soda and consuming so much sugar overall. And, sure enough, NHANES data were showing that the number of people with obesity had stabilized. This seemed connected, at the time. “We’ve halted the progress of the obesity epidemic,” William Dietz, an obesity physician-researcher who was then a CDC official, told the Times. Dietz, who had played a central role in creating the idea that obesity was an “epidemic” in the first place, chalked up that achievement to increased awareness of the problem and improvements to school-lunch programs.

Yet this progress turned out to be short-lived. In retrospect, the obesity-rate “plateaus” during those years now appear to be a trend-line blip, if not a statistical mirage. That’s not to say the CDC’s analyses were mistaken. The survey’s error bars were wide, and in those years, any increase in the numbers was not statistically significant. But over time a clear and upward drift became unmistakable. As of 2004, NHANES data showed that about one-third of American adults qualified as having obesity. By 2018, the proportion had moved past 40 percent.

Now Cynthia Ogden, the CDC’s branch chief for NHANES analysis, and her colleagues are reporting another flattening, set against a decades-long increase. Once again the error bars are wide, which is why the CDC’s data brief asserts that the apparent drop in the obesity rate, from 41.9 percent to 40.3 percent, is better understood as a new plateau. “We’re not going up at the same level as we did,” Susan Yanovski, a co-director of the NIH Office of Obesity Research, told me, “but I don’t think we can necessarily say that it’s a real decrease.” In the meantime, the new data clearly show that the rate of severe obesity among U.S. adults has continued to increase.

If we are indeed at a new plateau for Americans generally, then its cause is not yet clear. David Ludwig, an endocrinologist at Boston Children’s Hospital who has been skeptical of earlier “peak obesity” claims, told me that new drugs such as Ozempic certainly should be having some effect by now. “Even if a notable minority is taking the drugs and losing weight, that’s going to alter the shape of the curve, the prevalence rates, and related statistics,” he said. “So it would be surprising, and very depressing, for us not to see any impact of these extremely costly drugs by this point.” Burn-Murdoch, who seems to be working from the same assumption, points out that the recent improvement in obesity numbers looks better among people with college degrees than anyone else. This is just what you might expect, he argues, because the uptake of GLP-1 drugs is generally associated with education.

Yet if the Ozempic effect really were showing up in NHANES data, you’d also expect it to appear first in women, who are much more likely than men to be taking GLP-1s for obesity. This is not borne out in the data: America’s obesity rates appear to have come down (or leveled off) more quickly for men in the past few years. We also don’t know how many Americans were actually taking the drugs at the time of the latest surveys. I asked Ogden when she might expect the drugs to start moving the needle: What proportion of Americans would have to be taking GLP-1s for the national obesity rate to change? “That’s a good question,” she said. “All we can say is what these estimates show us right now, and that we really do need more data to see what’s really happening.”

Yanovski was similarly wary of ascribing any recent changes in the trend to GLP-1s. She suggested that other factors might be at play: fewer people eating out; reduced sugar consumption; shrinkflation in the food industry, which results in smaller average portion sizes. (In principle, COVID might have been a factor too, because the disease is much more deadly for those with severe obesity. In that case, though, you’d expect the number of Americans in that category to have dropped, when in fact it has gone up.) And both Yanovski and Ludwig have long been floating the possibility that, even if the food environment remains as toxic as ever, the effects could start to wane as a function of biology. Almost half the variability in body weight is genetic, Yanovski told me, and that fact in itself could put a ceiling on the long-term trend. “You reach a level in which the population, everybody who is at risk for developing obesity, has already done so,” Ludwig said.

The final possibility is that this new “plateau” will soon reveal itself to be yet another narrow step on a staircase that is always going up—just another artifact of noise, or else a temporary aberration. Having covered these reports for 15 years, I feel safe in saying that some degree of pessimism should be the default setting.

Then again, having covered these reports for 15 years, I’ve never seen an intervention as dramatic as Ozempic, in terms of its power and popularity. Earlier this year, I profiled Barb Herrera, a woman who has had obesity throughout her life, and has tried almost every intervention to reverse it: diets, fen-phen, bariatric surgery. In 2022, her body mass index was measured at 75; after many months of taking GLP-1 drugs, she has lost 255 pounds. If Herrera were included in the next NHANES survey, she’d be recorded with a BMI of less than 28—below the diagnostic threshold for obesity—and classified as “overweight.”

How many other Americans have crossed that line? We’ll soon find out. The next NHANES data surveys are slated to begin in January, Ogden told me, with the first results due back in early 2027, including, this time, information on people’s use of prescription drugs. If the nation has really passed the point of peak obesity—and if the GLP-1 drugs really are responsible—then we’ll know soon enough.