ITHACA, N.Y. -- Contrary to what many people believe, preschool children do not adjust how much they eat in response to how much they ate at their last meal or in the past 24 hours or how calorie-rich their meal is. By far, the most powerful predictor for how much children eat is how much food is put on their plate, concludes a new study by Cornell University researchers.

"We examined all the predictors we could of how much a child eats at a meal," said David Levitsky, professor of nutritional sciences and of psychology at Cornell. "We found that portion size is, by far, the most important factor in predicting how much a child will eat. These findings suggest that both the onus of controlling children's weight -- both in causing overweight in children as well as in its prevention -- must rest squarely in the hands of parents and other caregivers."

Levitsky and Gordana Mrdjenovic, Cornell Ph.D. '00, monitored the food intake of 16 preschool children, ages 4-6, for five to seven consecutive days in day-care centers, and parents kept a food diary of what their children ate in the evenings and weekends.

"We found that the more food children are served, the more they eat, regardless of what they've eaten previously in the day, including how big their breakfast was," said Levitsky. "We also found that the more snacks children are offered, the greater their total daily food and calorie intake."

The study is published in the June issue of Appetite (44:3, pp. 273-282).

Although previous studies had suggested that children regulate their food intake much more precisely than adults, most of those studies were conducted in laboratories, not in natural settings where environmental factors can play a very powerful role in determining a child's food intake, Levitsky said.

A previous study by the two Cornell nutritionists similarly reported that children do not adjust for the amount of food they eat to compensate for how many sweetened drinks they have either at meals or between meals. And in a previous study, Levitsky, with a different co-author, reported that the more food young adults are served, the more they eat.

Childhood obesity is now considered an epidemic in the United States. According to the National Institutes of Health, the number of children who are overweight has doubled in the last two to three decades; currently one child in five is overweight. The increase is in both children and adolescents, and in all age, race and gender groups. Obese children are now developing diseases, such as type 2 diabetes, that used to occur only in adults. Researchers now know that overweight children tend to become overweight adults, continuing to put them at greater risk for heart disease, high blood pressure and stroke. Overweight children not only suffer more health problems but also social discrimination, which puts them at higher risk for low self-esteem and depression.

The study, which was part of the Ph.D. degree awarded to Mrdjenovic, was supported by the U.S. Department of Agriculture.