“Most people know that being overweight or obese is unhealthy, and if you eat too much that contributes to being overweight,” said Dr. James Krieger, clinical professor of medicine at the University of Washington and executive director of Healthy Food America, an advocacy group. “But just telling people there’s a problem doesn’t solve it.”The latest data from the National Health and Nutrition Examination Survey come at a time when the food industry is pushing back against stronger public health measures aimed at combating obesity.

In recent NAFTA negotiations, the Trump administration has proposed rules favored by major food companies that would limit the ability of the United States, Mexico and Canada to require prominent labels on packaged foods warning about the health risks of foods high in sugar and fat.

While the latest survey data do not explain why Americans continue to get heavier, nutritionists and other experts cite lifestyle, genetics and, most importantly, a poor diet as factors. U.S. fast-food sales rose 22.7 percent from 2012-2017, according to Euromonitor, while packaged-food sales rose 8.8 percent.

The latest survey data found that U.S. youth are faring somewhat better than adults. Among Americans ages 2 to 19, 18.5 percent were obese in the 2015 and 2016, while 5.6 percent were severely obese. (A severely obese youth is defined as being 120 percent above the 95th percentile of body mass index for age and gender.)

The study found that the percentage of youths who are obese and severely obese rose slightly from the 2007-2008 time frame, but not enough to be statistically significant.

Dr. Craig Hales, co-author of the survey research, said that the small increase in childhood obesity “could be due to sampling error,” and that the upshot was “no increasing or decreasing trends over the last 10 years.”

“Something different is happening with adults and youth,” he said, adding that he wasn’t able to explain the reasons.

One group of youths that has seen statistically significant weight gain are the youngest children, ages 2 to 5. Obesity rates in this group rose to 13.9 percent in 2015 and 2016 from 10.1 percent in 2007 and 2008.

Scholars who study childhood obesity disagree about whether childhood obesity has plateaued or is increasing.

“We haven’t turned the tide. If anything, rates are continuing to climb upwards,” said Dr. David Ludwig, a nutrition professor at the Harvard T.H. Chan School of Public Health.

The 18.5 percent youth obesity rate in 2015-2016 marked an uptick following earlier years dating to 2007 and 2008 when it had held steady at about 17 percent.

Dr. William Dietz, director of the Stop Obesity Alliance at George Washington University, said that it is premature to reach any conclusions about the trend in childhood obesity.

“I’m worried about it for sure, but we need two more years of data,” he said. Still, he called the overall report “dismal,” given that the high rates of obesity mean high rates of disease and premature death.