"Doctors should encourage teens to limit their intake of food prepared away from home and to eat family dinners together, the benefits of which appear to include improved diet quality," said lead author Elsie Taveras, instructor in ambulatory care and prevention at Harvard Medical School (HMS) and Harvard Pilgrim Health Care (HPHC). She added that home dinners have been found to reduce high-risk adolescent behaviors such as tobacco, alcohol, and marijuana use. Taveras is also director of the One Step Ahead program at Children's Hospital Boston, which teaches families how to make healthy food choices.

"In today's fast food environment, it's a challenge for teenagers and their families to eat what's nutritious and healthful. When you are at your favorite restaurant, stay away from the fried foods and instead choose modest portions of grilled chicken or fish, a salad, or some fruit," said Matthew Gillman, senior author on the paper and associate professor of ambulatory care and prevention at HMS and HPHC.

Taveras and colleagues surveyed 14,355 children between 9 and 14 years old, and recorded their height, weight, physical activity, and frequency of consumption of fried food away from home. She found that over time, when the children increased the amount of fried foods they ate away from home, their body mass index (BMI) also increased. In the survey, this direct association was greatest among the youngest girls (ages 9 to 12). This finding could help doctors and parents to develop effective interventions to prevent excessive weight gain during this period of adolescence.

Adolescents in the study who ate fried food away from home more frequently reported higher total caloric intakes, intakes of saturated and trans fats, sugar-sweetened beverages, and red and processed meats, and higher glycemic loads. They also ate fewer foods that are integral to a well-balanced diet, like fruits and vegetables. Taveras's study suggests that eating fried food away from home is associated with dietary patterns leading to excessive weight gain (e.g., drinking sugar-sweetened beverages) and chronic diseases, such as heart disease (e.g. high consumption of trans and saturated fats), cancer (e.g. low consumption of fruits and vegetables), and type 2 diabetes (e.g. high glycemic load).

"Many of my patients, ages 8 to 12 years old, frequently eat foods prepared away from home, sometimes up to four times a week. If these early eating patterns persist throughout their adolescence, our findings suggest that these children will be heavier and perhaps be more at risk of chronic diseases," Taveras said. "We try to teach families how to make healthier choices when they choose to eat out and to encourage a well-balanced diet when eating in."

At the beginning of the study, 3.5 percent of girls and 6 percent of boys reported eating four to seven servings of fried food away from home per week. Overall, girls and boys 13 to 14 years old ate more fried food away from home than 9 to 12 year olds. At the end of the three-year study, the proportion of girls and boys who ate four to seven servings per week had more than doubled, to 7.5 percent and 12.7 percent, respectively.