Researchers say they have identified another risk factor for childhood obesity: school lunch.

A study of more than 1,000 sixth graders in several schools in southeastern Michigan found that those who regularly had the school lunch were 29 percent more likely to be obese than those who brought lunch from home.

Spending two or more hours a day watching television or playing video games also increased the risk of obesity, but by only 19 percent.

Of the 142 obese children in the study for whom dietary information was known, almost half were school-lunch regulars, compared with only one-third of the 787 who were not obese.

“Most school lunches rely heavily on high-energy, low-nutrient-value food, because it’s cheaper,” said Dr. Kim A. Eagle, director of the University of Michigan Cardiovascular Center, and senior author of the paper, published in the December issue of American Heart Journal. In some schools where the study was done, lunch programs offered specials like “Tater Tot Day,” he said.