Researchers said the finding may give parents one extra strategy to encourage youngsters to eat more greens, as childhood obesity rates continue rising and research suggests that kids lag well behind guidelines for fruit and veggie consumption.

With main courses, "you need to be careful and use the age-appropriate serving," said Sara Sweitzer, a nutrition researcher from the University of Texas at Austin.

"If they fill up on the entree, obviously the fruit and the vegetable are the last to get eaten," added Sweitzer, who was not involved in the new study.

Parents can make sure they are providing the right amount of food both by inspecting what's left in the lunch box when kids come home, and by talking to their kids about how much they eat.

"Go ahead and ask your child, 'Do you want a whole sandwich or do you want just half a sandwich?'" she advised.

For the new study, researchers at a Pennsylvania preschool served 17 kids six different variations of the same meal, one day each week for lunch. The meals had anywhere from less than half a cup to more than a cup and a half of macaroni and cheese, the main dish.

That was presented along with plenty of green beans and unsweetened applesauce, plus a whole grain roll and milk.

Jennifer Savage of The Pennsylvania State University in University Park and her colleagues found that the bigger the entree size, the more mac and cheese -- and the less of the healthy side dishes -- kids ate.

Preschoolers finished almost all of their smallest portion of mac and cheese, for an average of about 145 calories. However, they still ate the majority of much bigger portions and put away 390 calories worth of the main course when they started with the most on their plate.

When they were served the smallest entree, kids ate almost half of their healthy side dishes, including fruits and veggies, compared to only a quarter when they were served the biggest mac and cheese portion, Savage's team reports in the American Journal of Clinical Nutrition.

Kids' total lunchtime calorie counts varied based on entree size as well: they ate an average of 506 calories with the biggest portion, and 315 with the smallest.

Sweitzer said that packing too much of the main course for lunch is a problem she sees all the time with parents, in part because they're concerned they won't include enough food and their kids will be hungry.

"You will see parents pack the whole easy mac and cheese portion," she said. "That would be a huge amount -- it would be adequate for an adult to eat as part of lunch, and they'll pack that whole thing for the child to eat." 

And a four-year-old, she said, won't make balanced food choices on their own in that situation.

"If you give the child an option for a large portion of an entree food that they really like, they will eat that more and they'll fill up. They'll reach their satiety point and they'll just stop eating," Sweitzer told Reuters Health.

She added that another strategy to encourage kids to eat their fruits and veggies is for parents and older siblings to set a good example by choosing those as healthy snacks and making sure they're loading up on their nutrient-packed side dishes at meals.

 From the January 14, 2012, Prepared Foods' Daily News.