U.S. teens are eating healthier diets and showing less severe metabolic syndrome - a cluster of conditions like high blood pressure and elevated blood sugar that can lead to cardiovascular disease, stroke and diabetes - a new study suggests.

Adolescents are consuming fewer calories and carbohydrates and more healthy unsaturated fats than they were more than a decade ago, the analysis of U.S. survey data found.

Along with these shifts in eating habits, teens also developed increased levels "good" high-density lipoprotein (HDL) cholesterol that helps purge blood vessels of debris and lower levels of triglycerides - dangerous fats that can make blood thicker, stickier and more prone to clots.

"We found that the decrease in severity of the metabolic syndrome was driven by favorable changes in triglycerides and HDL cholesterol," said senior study author Dr. Mark DeBoer of the University of Virginia in Charlottesville.

"This supports the important idea that changes to your lifestyle choices are the key to improving cardiovascular risk status," DeBoer added by email.

Metabolic syndrome encompasses a combination of health risk factors - hypertension, obesity, elevated blood sugar, high triglycerides and low HDL cholesterol - that often occur together. Having metabolic syndrome is also associated with decreased sensitivity to the hormone insulin, which allows sugars to build up in the blood.

Left untreated, this syndrome can lead to serious health complications. The likelihood of developing the syndrome and severity of symptoms can be influenced by genetics, but may also be modified with diet and exercise, DeBoer and colleagues note in the journal Pediatrics.

To assess the interaction between changes in diet, exercise and metabolic syndrome severity over time, researchers analyzed nationwide survey data collected from 1999 to 2012 for 5,117 youth aged 12 to 19 years.

Overall, about 10 percent of teens in the study had metabolic syndrome. The prevalence didn't change over the study period despite a significant increase in what's known as body mass index (BMI), a ratio of weight relative to height that is used to track obesity.

Researchers didn't find changes in hypertension or blood sugar over the course of the study. They also didn't find changes in overall physical activity from 2007 to 2012 when the survey included exercise data.

Still, the severity of metabolic syndrome, calculated based on the presence and magnitude of individual risk factors, declined. Specifically, fewer kids had low HDL or high triglycerides by the end of the study.

But the study can't prove that dietary changes are what caused the decline in metabolic syndrome severity.

Another limitation of the study is that physical activity data was incomplete and relied on teens to accurately report on their exercise habits, which may have masked a connection between metabolic syndrome and fitness levels, the authors note.

"Sedentary individuals may over-report their physical activity while obese adolescents may under-report their eating," observed Benjamin Guinhouya, an epidemiology researcher at the University of Lille in France who wasn't involved in the study.

One in six U.S. children and teens are obese, according to the U.S. Centers for Disease Control and Prevention.

Because obese children and teens often have metabolic syndrome, studies like this are still important to understand how lifestyle changes might influence the severity of symptoms and potentially reduce the risk of heart disease and diabetes, Guinhouya added by email.

To help prevent metabolic syndrome, parents should keep an eye on children's weight and waist circumference, which unlike other risk factors can be simple to spot, Guinhouya said.

"Efforts should be carried out to keep the waist circumference of children to less than half their height," Guinhouya said. "This can be done through continuing to watch the eating choices of children together with encouragement and promotion of an active lifestyle and a reduction of sedentary pastimes."

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