(CNN) While obesity rates among young children in the United States appeared to be on the decline a few years ago, a new analysis suggests that it's not time to celebrate just yet.
Rather, there was a significant rise in severe obesity among children ages 2 to 5, since around 2013, according to the study published in the journal Pediatrics on Monday.
"A few years ago, there was also some hopeful evidence that obesity rates might be declining for preschool-aged children. Unfortunately, our data, looking at the same age group, show this decline now appears to be reversing," said Asheley Skinner, a health services researcher and associate professor at Duke University in Durham, North Carolina, who was first author of the study.
"This is not surprising, necessarily, but is disheartening. It tells us that our efforts to improve the health of children is not reaching across the country," she said. "We need to improve access to healthy food and physical activity, and do it in a way that recognizes that parents have stressful lives."
Obesity means a person has too much body fat and can increase the risk of diabetes, heart disease, stroke, arthritis, and even some cancers.
In the US, the percentage of children and teens affected by obesity has more than tripled since the 1970s, according to the Centers for Disease Control and Prevention. It's estimated that nearly one in five children and teens are obese. But obesity is not just an American problem.
In the United Kingdom, obesity is estimated to affect around one in every five children aged 10 to 11. Across the WHO African region, the number of overweight or obese children increased from 4 to 9 million between 1990 and 2016, according to the World Health Organization.
Globally, the number of overweight or obese infants and young children, up to 5 years old, climbed from 32 to 41 million over that same time period, according to WHO.
The new study used data on obesity rates across the US, between 1999 and 2016, from the CDC's National Health and Nutrition Examination Survey.
The researchers analyzed the data, taking a close look at the prevalence of overweight and obesity among children, 2 to 19.
They found a continuous upward trend of obesity since 1999, with significant increases among young children, 2 to 5, and teen girls, 16 to 19, from 2015 to 2016, compared with previous years.
"This study is important because it reminds us that obesity in children is not going away," Skinner said, adding that there are two reasons why these new findings appear to contradict previous reports.
First, "the differences in the studies are the different time periods. We have the most recent data available," she said. "Second, however, is that some studies have shown declines but have been based in smaller areas. We have seen some possible declines in certain school systems, which may have made beneficial changes that led to those changes."
The new study still had some limitations.
"The most important limitation is that this is a survey from across the US. We aren't looking at the same kids over time and saying more of them are developing obesity, but our findings should be relevant across the country," Skinner said.
Also, while the data set was nationally representative, there were small sample sizes for certain subgroups within the data, such as particular age groups and racial and ethnic groups.
Kenneth Thorpe, chairman of the Partnership to Fight Chronic Disease and a professor at Emory University's Rollins School of Public Health in Atlanta, said that the study used reliable data and these new findings on childhood obesity did not surprise him.
"I've seen the very recent data that just came out on trends in obesity among adults, and it's following the same type of trend," Thorpe said about the study. "About 40% of adults are now considered obese, and the trends look very similar to what I see here for boys and girls, rising over the last decade."
Thorpe believes there are several concerns that stem from this rise.
"One is that obesity by itself accounts for about 20% of what we spend on health care," he said. "Chronic diseases are linked to obesity. Whether it's high blood pressure, bad cholesterol, heart disease -- obesity is a risk factor of all of those things, and those are all key drivers of health care spending."
Dr. David Ludwig, professor of nutrition at Harvard School of Public Health and founding director of the Optimal Weight for Life program at Boston Children's Hospital, wrote an accompanying editorial in which he calls for the federal government to form an interagency commission on obesity to address the growing epidemic.
"The obesity epidemic threatens to shorten life expectancy in the United States and bankrupt the health care system. Yet progressive weight gain from one generation to the next is not inevitable," Ludwig wrote..
"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. What is lacking is an effective strategy to address these drivers with sufficient intensity, consistency, and persistence," Ludwig wrote.
"The battle against childhood obesity faces many obstacles, most notably entrenched special interests and a 'business as usual' mindset," he wrote. "But with political will and collaboration across key sectors of society, we can hopefully, soon, begin to end this worsening epidemic.