Many consider fruit juice to be a healthy alternative to eating a piece of fruit, but that’s not necessarily so. A new study shows just how much the nutritional quality of high school students’ diets suffers when fruit juice is an option.

According to the current recommendations from the American Academy of Pediatrics, children between the ages of 7 and 18 should not drink more than a cup of fruit juice a day.

Sales of bottles of water and fruit juice also went down — by 8 and 24 percent respectively — on days that juice was offered.

The National School Lunch Program contributes to the healthy diet of over 30 million students due to the fruits, vegetables and dairy foods served, but the role of fruit juice in the lunch program and in children’s diets is controversial. The program only serves juice on certain days.

Researchers at the Rudd Center for Food Policy and Obesity at the University of Connecticut used data collected from the cafeteria register at three high schools during one school year to see how juice affected students’ food choices on days when juice was served. Sales of beverages available for purchase separately, including water and fruit juice, were also included.

On the days that juice was an option during school lunch, students chose nearly 10 percent fewer milks and 7 percent fewer servings of whole fruit. Sales of bottles of water and fruit juice also went down — by 8 and 24 percent respectively — on days that juice was offered.

When juice was available, students tended not to choose whole fruit and milk as often, diminishing the nutritional quality of their lunches. According to Marlene Schwartz, co-author of the study and Director of the Rudd Center, when kids drink juice instead of eating fruit, they miss out on three nutrients that are important during adolescence — calcium, vitamin D and fiber.

“The potential nutritional impact of these substitutions is important to consider. For instance, an 8-ounce serving of apple juice has no vitamin D, 285 fewer grams of calcium and 116 fewer grams of potassium compared to an 8-ounce serving of 1% milk,” Rebecca Boehm, lead author of the study, and a postdoctoral fellow with the Rudd Center for Food Policy and Obesity and the Zwick Center for Food and Resource Policy, said in a statement.

It may be time to reconsider the policy of offering fruit juice as part of school lunch programs. Removing juice as an option will likely encourage students to choose milk or whole fruit more often and lead to healthier diets in adulthood.

The study is published in the Journal of Nutrition Education and Behavior.