American children are eating restaurant-prepared fried foods more frequently, leading to higher body mass index (BMI) and poor diet quality, according to a study conducted by Harvard Medical School (HMS) researchers.

The study, published in this month’s issue of the journal Pediatrics, examined 14,000 adolescents from all 50 states over a period of three years.

Lead author Dr. Elsie M. Taveras—an instructor at HMS and director of a pediatric obesity-prevention program at Children’s Hospital in Boston—and other researchers recorded the children’s weight, height, physical activity, and the frequency with which they consumed restaurant-served fried foods.

They found that the number of children who ate fast food between four and seven times per week more than doubled over the three-year period during which the study was conducted.

The HMS study also found that nine to 14-year-olds who increased their consumption of fast food gained weight at faster than normal rates. Boys who ate fried food away from home more than four times per week had a BMI of 19.3, while boys who did not eat fried foods as often had a BMI of 19.1. A BMI of 25 is considered clinically overweight.

While the difference in BMI between those who eat fast food frequently and those who do not may appear small, Taveras said that with poor eating habits, changes in BMI can accumulate over time.

“Our study shows that if children continue to eat large quantities of fried food away from home they will continue to gain weight,” Taveras said.

Unlike previous studies that documented the relationship between fast food and obesity, Taveras’ study also looked at the effects of fast food consumption on diet quality.

“We found that participants who ate FFA (fried foods away from home) reported higher intakes of total energy, whole dairy foods, sugar-sweetened beverages, red and processed meats, and trans fat, as well as higher glycemic loads,” the authors wrote in the study. “They also consumed less low-fat dairy foods, fruits, and vegetables.”

The authors emphasize in the study that the effect of fast food on diet quality is particularly alarming, since an inadequate, unbalanced diet may lead to heart disease, cancer, and type 2 diabetes.

Taveras said the best way to fight rising BMI and poor diet quality in children is to limit fried food intake.

“Making healthier choices when they are eating away from home, such as consuming fruits and vegetables, will help. Our study also suggests that eating more family dinners would be beneficial,” she said.

Taveras noted that because all the study’s subjects are the children of registered nurses, the findings may not apply to the general populace.

“The participants of our study are the children of nurses so our study may be influenced by a variety of socio-economic and ethnic factors,” she said.