"Although fast foods are generally recognised as less healthful, our study found that foods consumed by US children from grocery stores and schools were similar in empty calorie content to fast foods," author Jennifer M. Poti said.
Poti is a doctoral candidate in nutritional epidemiology at the University of North Carolina at Chapel Hill. The 2010 Dietary Guidelines for Americans recommend for kids and adults that a maximum of between 8% and 19% of their daily calories should be "empty", that is, coming from added sugar or solid fat.
Solid fats include those solid at room temperature, including butter, meat fats and hydrogenated oils. Added sugars are incorporated during food processing, preparation or at the table, but do not include the natural sugars in fruit or milk, Poti said.
Calorie consumption analysis
These fats and sugars add lots of calories but few nutrients to food. Getting too many empty calories can lead to weight gain and obesity, she said.
The new study, which analysed data from a 2010 nationwide survey covering more than 3 000 kids ages 2 to 18 years old, looked at the calories consumed from three primary food sources: grocery or convenience stores, schools and fast food restaurants.
At each location, about a third of the children's average calorie intake was "empty calories". In food purchased from stores, 33% of calories were from fats and added sugars. In food from fast-food restaurants, it was 35%, and school-bought foods were 32% empty calories.
Kids tended to get most of their food from stores, so that location provided the highest total empty calories an average of 436 calories daily according to the results published in the Journal of the Academy of Nutrition and Dietetics.
Sugary drinks and grain-based desserts like cakes were big empty calorie sources at each of the locations. Whole or two percent milk was also a common source from stores and at school. The study also pointed the finger at pizza from schools and pizza and French fries from restaurants as major contributors to daily totals for empty calories.
Store-bought foods tended to have more sugar and less fat, whereas the reverse was true for fast foods. School food fell in the middle on both counts."Our study found that 20% of pizza and 22% of high-fat milk consumed by kids are provided by schools, and 72% of sugar-sweetened beverages like sodas, fruit drinks, sports drinks and energy drinks consumed by kids are obtained from grocery stores," Poti said.
Efforts to improve kids' diets should be aimed at all three locations, she said. Since the top empty-calorie food sources were different at the three locations, strategies to reduce empty calories may need to vary by location, she said.
"The data analysed in our study was collected before implementation of the new nutrition standards for the National School Lunch and Breakfast Programs, established by the Healthy, Hunger-Free Kids Act of 2010," Poti said.
These results could be an important baseline for gauging how effective more recent changes have been, she said."The new US Department of Agriculture lunch rules that went into effect last year require only lower-fat milks, and proposed standards for vending machines and other venues also require lower-fat milks, but those standards have not yet gone into effect," said Lindsey Turner, a health psychologist and research scientist at the Institute for Health Research and Policy at the University of Illinois at Chicago.
"In our Bridging the Gap research studies of K-12 schools nationwide, we found that even just two years ago, many schools offered higher-fat milks at lunch," said Turner, who was not involved in the new study, but has conducted similar research in schools.
Pizza is available most days or every day in most high schools, she said. "It will be essential to keep tracking whether schools are implementing the new nutrition standards and removing unnecessary sources of sugar and fat that contribute to empty calories for children and adolescents," she said.
Current guidelines don't require added sugar or solid fats to be indicated on nutrition facts panels for packaged foods. But parents can keep track of saturated and trans fats, which are the main types of solid fats, and total sugar levels which are included on labels, Poti said.
The recent Food and Drug Administration ruling that trans fats are no longer "generally recognized as safe" could help to reduce children's empty calorie intake if trans fats are removed and not replaced with other solid fats, she said.