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School-age children ate more fruits and vegetables when they had to sit at the lunch table for 20 minutes versus half that long, results of a small randomized trial indicated.

With 38 children ages 8-14 participating at an Illinois summer camp, those with the 20-minute requirement ate 84.2% of the fruits and 65.3% of the vegetables served to them, compared with 72.9% and 51.2%, respectively, among those who were required to stay seated for just 10 minutes, according to Melissa Pflugh Prescott, PhD, and colleagues at the University of Illinois at Urbana-Champaign.

These differences -- 11.3 percentage points for fruits and 14.1 points for vegetables -- were both statistically and nutritionally significant, the researchers reported in . They equated to nearly 10 extra grams each for fruits and vegetables per lunch.

Consumption of entrees and drinks (water and milk were the only ones provided), on the other hand, did not differ significantly between seating conditions, though there were trends toward increased intake of these as well with the 20-minute requirement.

Overall, 20-minute seating was associated with increased mean consumption of all individual nutrient types -- calories, fats, carbohydrates, fiber, protein, vitamin D, calcium, potassium, and iron -- for the point estimates. These were statistically significant for total calories, carbs, fiber, protein, iron, and potassium.

"These results support a 20-minute seated lunch policy, which could improve diet quality and reduce food waste in children," Pflugh Prescott and colleagues concluded.

The findings aren't a big surprise, as a number of observational studies had also linked lunch seating time to the amount of food consumed. Both the American Academy of Pediatrics and the CDC , Pflugh Prescott's group pointed out.

But those studies hadn't accounted for a number of potential confounders, such as kids' food preferences when given choices, nor the potential for "social behaviors" including talking and smartphone use to alter their eating habits. Pflugh Prescott and colleagues sought to address those in their trial.

Called the study used a cross-over design to expose participants to both seating requirement conditions an equal number of times. Five different food assortments were offered during the 4-week study, each available four times, randomized to the 10- or 20-minute seating requirement such that each appeared twice during each condition. Children, whose mean age was about 12 (SD 1.2), could then select the foods they wanted from these menus.

The research team also kept watch on participants during lunch, tracking how often they stood up, talked with other children, used their phones, and when they left the table. Children were asked to rate their meals as well.

When required to stay seated for 20 minutes, "talking ratings" were more than one-third higher (P<0.001) than with the 10-minute mandate, but phone use did not differ significantly.

Actual mean seating time hewed closely to the minimums: about 12 minutes for those with the 10-minute requirement and 22 minutes under the 20-minute requirement. Participants left their seats during lunch for less than a minute, on average. There were no differences in participants' liking for their lunches by seating condition.

As always, the trial came with some limitations. Because participants came and went from camp, some did not receive every menu under both the 10- and 20-minute conditions. Most participants with race/ethnicity recorded were white, and some 60% were girls, restricting the generalizability somewhat. And that the study took place at a camp and not a regular school could have affected the results.

Pflugh Prescott and colleagues acknowledged that the small sample size could be seen as another limitation, but they argued that, thanks to the cross-over design, it remained "adequately powered to detect significant differences in fruit and vegetable consumption."

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