Americans’ obesity rates have reached a new high-water mark. Again.

In 2015 and 2016, just short of four in 10 American adults had a body mass index that put them in obese territory.

In addition, just under two in 10 American children — those between 2 and 19 years of age — are now considered obese as well.

The new measure of the nation’s weight problem, released early Friday by statisticians from the U.S. Centers for Disease Control and Prevention, chronicles dramatic increases from the nation’s obesity levels since the turn of the 21st century.

Adult obesity rates have climbed steadily from a rate of 30.5 percent in 1999-2000 to 39.8 percent in 2015-2016, the most recent period for which data were available. That represents a 30 percent increase. Children’s rates of obesity have risen roughly 34 percent in the same period, from 13.9 percent in 1999-2000 to 18 percent in 2015-2016.

Seen against a more distant backdrop, the new figures show an even starker pattern of national weight-gain over a generation.

In the period between 1976 and 1980, the same national survey found that roughly 15 percent of adults and just 5.5 percent of children qualified as obese. In the time that’s elapsed since “Saturday Night Fever” was playing in movie theaters and Ronald Reagan won the presidency, rates of obesity in the United States have nearly tripled.

The new report, from the National Center for Health Statistics, measures obesity according to body mass index. This is a rough measure of fatness that takes a person’s weight (measured in kilograms) and divides it by their height (measured in meters) squared. For adults, those with a BMI between 18.5 and 24.9 are considered to have a “normal” weight. A BMI between 25 and 29.9 is considered overweight, and anything above 30 is deemed obese.

Obesity rates for children and teens are based on CDC growth charts that use a baseline period between 1963 and 1994. Those with a BMI above the 85th percentile are considered overweight, and those above the 95th percentile are considered obese.

The report underscores a continuing pattern of racial and ethnic disparities when it comes to weight. Obesity rates among African-Americans and Latinos have been consistently higher than those seen in whites, and the new survey shows no change in that pattern.

In adult Latinos and non-Hispanic blacks, obesity rates for 2015-2016 were 47 percent and 46.8 percent, respectively. Some 37.9 percent of non-Hispanic white American adults were obese in the latest tally.

Among non-Hispanic Asian adults, obesity rates were at 12.9 percent.

The racial and ethnic disparities were heavily driven by women: while white men and women were equally likely to be obese, rates of obesity in black women (54.8 percent) and Latinas (50.6 percent) were strikingly higher than among their male counterparts (36.9 percent and 43.1 percent, respectively).

Patrick T. Bradshaw, who studies population health at the University of California at Berkeley, said the new statistics underscore that turning the tide on obesity will require more aggressive and targeted efforts.

The rising obesity levels “suggest that we haven’t been successful in efforts to reduce or prevent obesity in the population,” Bradshaw said. He echoed a growing consensus among public health experts that if progress is to be made in driving down obesity rates in the population at large, campaigns may need to focus on the specific challenges faced by Latinos and African Americans — especially women — in weight management.

The report does suggest a very modest measure of progress in the fight to reduce obesity rates. Compared to obesity prevalence data from 2013 and 2014, the newly reported rates do not represent a statistically significant change.

BMI is widely criticized as an imperfect way to gauge an individual’s health prospects. Aerobic fitness levels and waist-to-hip ratio are sometimes viewed as better measures.

But the BMI’s near-ubiquitous use in research on weight and disease risk has yielded unmistakable evidence of obesity’s dangers. In large populations, research has shown, higher rates of obesity shorten lives and drive up the incidence of cancer, cardiovascular disease and chronic conditions such as diabetes and arthritis.

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