I wrote recently that 100 percent fruit juice, while it's packed with the nutrients lacking in more diluted fruit drinks, is still caloric, so it shouldn't be consumed with impunity. That's true, but there's some good news for parents whose kids prefer their fruit in liquid form: Most kids and teenagers who consume 100 percent juice don't gain weight. Those studies reviewed by researchers that did find a weight gain found it in already overweight kids or adolescent girls.
One caveat is that the studies that were reviewed can't show cause and effect; there might be some other reason these kids didn't gain weight. For example, kids who drink fruit juice rather than soda may be healthier in other regards, too. But the takeaway from this review is that drinking 100 percent fruit juice (we're not talking here about the less nutritious but often equally caloric fruit "cocktails" and other drinks) in moderate amounts is probably not going to make your otherwise healthy kids overweight and may help them meet their nutrient requirements.
That said, fruit is still preferable. It contains fiber, which has its own benefits. (See my earlier post on fruit drinks for the details.) And for a kid or teenager who is already overweight, whole fruit delivers those nutrients with fewer calories. The full study, published in the American Journal of Lifestyle Medicine, is available online here (.pdf) for a limited time.