Preschoolers with a taste for fruit juice may pack on excess pounds, but only if they already have a tendency toward being overweight, a new study suggests.

Some past studies have linked children's intake of sugary fruit juice to excess weight gain, but others have failed to find such a relationship.

Despite the question mark, though, experts still generally recommend limiting children's juice drinking; the American Academy of Pediatrics (AAP) suggests that children ages 1 to 6 drink no more than 4 to 6 ounces of juice per day.

In the new study, published in the journal Pediatrics, researchers found that the higher a child's juice intake, the greater the gain in body fat over time, but only among children who were initially overweight or on the verge of becoming so at the study's outset.

In contrast, children who ate more whole fruits tended to put on less body fat.

The findings add to evidence that too much fruit juice can contribute to excess weight gain in children, but particularly among those who are most at risk of becoming obese adults, said lead study author Dr. Myles S. Faith of the University of Pennsylvania School of Medicine in Philadelphia.

The results may surprise some parents who think of fruit juice as a health food of sorts. "Many parents equate fruit juice with whole fruits," Faith noted in an interview.

However, juices typically contain added sugar, and therefore, calories. In addition, Faith said, there is basic research that suggests the body regulates beverage intake differently than solid food.

These studies indicate that while people may compensate for indulging in too many cookies by eating less later in the day, the same is not true when we down excess liquid calories.

Faith and his colleagues based their results on data from 2,800 children ages 1 to 4 who were receiving food assistance from the federal government's WIC program. They collected information on each child's diet, and then measured their weight and height every 6 months for up to four years.

In general, the study found, children who were overweight or nearly so tended to put on more body fat as their juice intake increased. This was with other factors, including overall diet, considered.

The same was not true of children who were normal-weight when the study began, Faith and his colleagues found.

Still, Faith said the AAP's recommendations on limiting juice intake are good guidelines for both overweight and thin children. Water, whole fruits and vegetables, and low-fat milk are "sound substitutes" for juice, he noted.

"The message is not that children should not drink fruit juice," Faith said, but that the amount be appropriate.

The fruit juice boxes so popular with kids typically contain about 100 calories each. So a few of those each day, Faith noted, can start to add up.