Obesity is worsening in American kids, researchers reported Monday.

And the most severe obesity is hitting more and more very small children — those under the age of 5, they found.

Experts blame a society that continues to push junk food despite the overwhelming evidence about its dangers, and the lack of access to exercise.

More than 40 percent of 16 to 19-year-olds are obese, the team at Duke University, Wake Forest University and elsewhere found. But worse, 26 percent of 2 to 5-year-olds were overweight and more than 15 percent were obese, they reported in the journal Pediatrics.

“Despite previous reports that obesity in children and adolescents has remained stable or decreased in recent years, we found no evidence of a decline in obesity prevalence at any age,” the team, led by Duke’s Asheley Cockrell Skinner, wrote.

And it looks like efforts to turn things around are gaining little headway.

“Despite intense focus on reducing the U.S. childhood obesity epidemic over the past two decades, our progress remains unclear,” they added.

For instance, former first lady Michelle Obama’s “Let’s Move” campaign aimed to encourage exercise and healthy eating, while various states, cities and local authorities have tried to encourage exercise and to make junk food sweetened soft drinks less appealing and available.

It’s not that the efforts have failed because they are of no use, the team added. It’s because they are nowhere near enough. “More resources are clearly necessary,” they wrote.

And television shows stressing crash diets do not help.

“There are few long-term studies of obesity development or treatment outcomes because this work is occurring in a Biggest Loser environment, with the focus being on short-term changes in weight that we are only beginning to see as an erroneous pursuit in adult populations,” they wrote.

It's a lifetime sentence. Overweight kids usually grow up to be overweight as adults.

It’s not as if the threat of obesity is not understood, said Dr. David Ludwig, a specialist in weight gain at Boston Children’s Hospital. “The obesity epidemic threatens to shorten life expectancy in the United States and bankrupt the health care system,” Ludwig wrote in a commentary.

“We have deep knowledge of the biological drivers of obesity, which include poor diet quality, excessive sedentary time, inadequate physical activity, stress, sleep deprivation, perinatal factors, and probably environmental endocrine-disrupting chemicals,” Ludwig added.

“What is lacking is an effective strategy to address these drivers with sufficient intensity, consistency, and persistence. It is not enough for a child to receive more healthful meals at school (which is not always the case) if she encounters a gantlet of junk food after school and in the home.”

Parents often do not help, either. A report published earlier this month in the journal Health Promotion Practice found 53 percent of parents in Arkansas did not believe reports cautioning them that their children were obese.

Researchers calculate obesity using Body Mass Index or BMI, a ratio of height to weight. For children, BMI is measured by their height and weight compared to the norm for children the same age.