Snack Attack!

Children and snacks are made for each other. Indeed, the smaller size of young kids' stomachs combined with their often frenetic activity levels pretty much requires that they nibble a little something between meals. Nutritionists have long suspected, however, that changes in America's snacking habits go a long way toward explaining why young people in the U.S. have grown so fat over the past 30 years. Just last month the Centers for Disease Control reported that 13% of children ages 6 to 11 are overweight, up from 11% in the early 1990s and 4% in the 1960s.

Now comes word that snacks are in fact a bigger culprit than anyone realized. By analyzing data from three national food surveys, researchers from the University of North Carolina determined that children are eating a lot more snacks than they did three decades ago. How much more? Kids today consume 25% of their calories between meals, compared with 18% in the 1970s. The biggest changes occurred after 1989, mirroring the rapid increase in childhood obesity.

What most surprised the research team led by Barry Popkin, professor of nutrition at U.N.C.'s School of Public Health, was the fact that today's snacks are packed with a greater concentration of calories than ever before. That jump in what nutritionists call "energy density" raises plenty of red flags, because the more calories per gram in a particular snack, the easier it is to overeat.

This high-energy trap fools lots of folks, not just kids. After all, our bellies don't add up calories to calculate when we should feel full; it seems to be more a question of the volume and composition of the food we eat. Consider which you would be more likely to do: reach for another chocolate-chip cookie after you've already finished three in a row or bite into another apple after you've polished off three apples? If you're like me, the cookies win hands down. Yet the average chocolate-chip cookie contains 5 calories per gram, compared with the apple's 0.6. Bottom line: the less calorie-dense apples fill you up faster.

It's not as if kids ate only fruits and veggies in the 1960s. But other popular snacks of that era were less processed, according to Popkin. "The biggest shift is away from milk and toward soft drinks," he says. Other particularly noteworthy changes include a jump in salty snacks and the advent of "high-energy" bars that deliver, along with their vitamins, a concentrated dose of calories.

The solution is not to ban snacks from your household. Focus instead on those that are healthier for your children--and for you. Low-fat milk, a rich source of calcium, is better than sodas or juice drinks for most children. (Kids who have trouble digesting lactose often do well with yogurt or lactose-reduced milk.) Try freezing grapes or serving carrot sticks with salsa. But make sure you don't create a backlash against fruits and vegetables by emphasizing how good for you they are. That only makes potato chips and brownies seem all the more appealing.

Meanwhile, make sure your kids spend more time on the playground than at their PlayStation. Physical activity will boost their metabolism and tone their bodies. They'll also be more likely to exercise and eat right if Mom and Dad set a good example.