Do you know what your kids are eating?

Despite a government mandate that school lunches and breakfasts meet federal dietary guidelines, some middle school students eat one-half, rather than the recommended one-third, of their daily allowance of fat in school cafeteria lunches, according to a recent study.

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University of California-San Diego researchers looked at the food environment at 24 middle schools in San Diego County, Calif., calculating the total fat and saturated fat served in cafeteria lunches and breakfasts, a la carte items, student-run stores and bag lunches brought from home. Along with collecting information on the quantity of each item sold, the researchers also surveyed children on their daily menu choices.

They found that school-provided lunches had the highest fat content of the school food offerings they examined. But school breakfasts, "a la carte" dining items such as pizza and baked goods, and chips and candy sold at student-run stores all contributed to "excessive" fat consumption by students, lead researcher James Sallis said.

The study is published in a recent issue of the journal Preventive Medicine.

"We estimated that the average student consumed about 26 grams of total fat at school, 30 percent more than the 20 grams recommended, and 14 percent more saturated fat than recommended," Sallis said.

Their analysis revealed that cafeteria lunches contained an average of 31.1 grams of fat, while bag lunches had an average of 20.8 grams of fat. Meanwhile, cafeteria breakfasts contained an average of 14.4 fat grams, a la carte items had an average of 13.1 fat grams and items from student stores had an average of 6.4 fat grams.

The federal dietary guidelines recommend eating 65 grams of fat per day. Earlier studies have found that students eat 33 percent of their daily food intake at school, meaning that only about 20 grams of fat should be consumed as part of the school-day diet.

Based on the percentage of students who ate each category of food, the researchers concluded that cafeteria lunches contributed the most to the average daily fat intake, accounting for 42 percent of the fat eaten by students at school. A la carte items were also a major contributor, providing 27 percent of the total fat eaten at school.

"We believe that students may choose the higher fat options, the pizza over the chef salad, within the cafeteria lunch, so that the average lunch has more than 30 percent of its calories from fat," Sallis said.

Researchers said they were surprised to find that bag lunches were relatively low in fat.

"It does look like kids are choosing wisely when they pack their lunch," study co-author Michelle Zive said.

The researchers also found a link between a la carte service and the average socioeconomic status of a school's population. In wealthier schools, students bought more a la carte items than in poorer schools. But poorer schools tended to stock more high-fat items than wealthy schools.

The researchers said schools should introduce lower fat versions of popular foods, reduce the price of low-fat items, introduce more low-fat eating options and creatively market low-fat foods to students to bring down overall fat consumption.