American adults continue to put on the pounds. New data shows that nearly 40 percent of them were obese in 2015 and 2016, a sharp increase from a decade earlier, federal health officials reported Friday.

The prevalence of severe obesity in American adults is also rising, heightening their risks of developing heart disease, diabetes and various cancers. According to the latest data, published Friday in JAMA, 7.7 percent of American adults were severely obese in the same period.

The data — gathered in a large-scale federal survey that is considered the gold standard for health data — measured trends in obesity from 2015 and 2016 back to 2007 and 2008, when 5.7 percent of American adults were severely obese and 33.7 percent were obese. The survey counted people with a body mass index of 30 or more as obese, and those with a B.M.I. of 40 or more as severely obese.

Public health experts said that they were alarmed by the continuing rise in obesity among adults and by the fact that efforts to educate people about the health risks of a poor diet do not seem to be working.