BAKERSFIELD, Calif. -- The rate of obesity in American children continues to creep up -- rising from 14.8 percent in 2003 to more than 16 percent in 2007 among kids 10 to 17 years of age.

A major reason for the increase? American kids are eating more than they should.

A new study has found that kids are snacking more than ever -- nearly three times per day -- and this has added 168 calories per day to their diets since 1977.

Researchers at the University of North Carolina, Chapel Hill analyzed decades of eating behavior among kids and found that snacks now comprise 27 percent of the calories in children's diets. And they aren't choosing healthy foods either -- since the late '70s, kids are snacking on less fresh fruit and milk and more junk food such as cake, candy and chips.

Experts said the excess calories are bad, but it's the high sodium and fat content in these snacks that may be truly damaging for kids' health in the future.