Schools may be shorting their students on a nutritious lunch by keeping breaks short, a new study finds. According to a report from the Harvard Gazette, students that have fewer than 20 minutes to eat their lunches typically consume a fraction of their main dish, milk and vegetables compared to those who aren’t rushed.

The study, led by Juliana Cohen at the Harvard Chan School’s Department of Nutrition, was published yesterday in the Journal of the Academy of Nutrition and Dietetics. It found that many children, “especially those from low-income families, rely on school meals for up to half their daily energy intake.” Cohen says it’s absolutely necessary that these children get enough time to finish their lunches.

The National School Lunch Program feeds over 30 million kids in more than 100,000 schools across the country. Many students have lunch periods that last 20 minutes or less, which the authors say is not enough time to eat a healthy lunch.

The study examined 1,001 students across six elementary and middle schools whose lunch periods ranged from 20 to 30 minutes in schools in a low-income urban district. The schools were participating in the Modifying Eating and Lifestyles at School (MEALS) study, a joint effort between Harvard Chan School and Project Bread. They compared the available nutrition with the amount that was left on the students’ plates at the end of a lunch period.

The study found that students who had less than 20 minutes to eat finished 13 percent less of their entrees, 12 percent less of their vegetables, and 10 percent less milk than students who were given a minimum of 25 minutes to eat lunch. It also found that students with fewer time to eat were less likely to choose a fruit as part of their lunch.