To combat the escalating rates of childhood obesity, parents should go beyond what is on their children's plate and look at what is filling their glass, suggests a new study presented at the Experimental Biology scientific conference.

The study found that no other single food provides more calories to a teenager's diet than sodas and fruit drinks. In all, these sweet drinks provide about 13% of a teenager's total calories -- more than cakes, cookies and other sugary foods. Sodas and fruit drinks are also the single leading source of added sugars in a teen's diet, providing more than half of all added sugars they consume.

Researchers from the University of Vermont, University of British Columbia, and ENVIRON Health Sciences Institute studied the diets of more than 3,000 children and teenagers ages 2-18 using food consumption data from the government's recent National Health and Nutrition Examination Survey. They found that consumption of sodas and fruit drinks increases in a step-wise fashion as U.S children get older, while milk intake declines in a similar way -- suggesting that milk is being displaced by soft drinks and juice drinks. By the time a child enters adolescence, he or she is drinking about twice as many sugary sodas and fruit drinks as milk.

"Our study found that milk is a primary source of nutrients in a child's diet, but milk consumption steadily declines as children grow older, which may prevent older children and teenagers from consuming the nutrients they need for growth and development," said lead researcher Mary M. Murphy, RD of ENVIRON Health Sciences Institute, who presented the findings.

Despite the decline in milk intake as children reach their teen years, the beverage remains the number one source of several key nutrients -- including calcium, phosphorus, magnesium and potassium. Calcium and potassium are chronically low in a teenager's diet, and both were highlighted as "problem nutrients" in the recently released Dietary Guidelines for Americans.

The new study also found that milk is among the top four food sources of protein, vitamin A and zinc for both children and teens.

Flavored milk is an increasingly popular choice for teenagers, yet the study found that there was little impact on the amount of added sugars it provided. Chocolate milk and other flavored milks contributed only 2% of the total added sugars in a teen's diet, compared to 50% or more that soft drinks and fruit drinks provided.

"Flavored milk may be a good strategy to prevent the switch from milk to soft drinks," said co-author Rachel Johnson, professor of nutrition and dean of agriculture and life sciences at the University of Vermont. "It's important that we intervene to reverse this troubling trend," said Johnson, who has conducted previous research showing that flavored milk helped children and teens meet calcium recommendations without increasing the amount of added sugars in their diets.

The shift from milk to sodas and fruit drinks can be damaging to a teen's bones, according to co-author Susan Barr, professor of nutrition at the University of British Columbia. Research suggests a shortage of the calcium provided by milk during the teenage years could lead to a failure to maximize bone mass, setting the stage for osteoporosis in the future.

Additional studies indicate that too little milk combined with too many soft drinks are contributing to the problem of childhood obesity. Researchers have found that teenagers who drink more milk instead of sodas tend to weigh less and have less body fat. Alternatively, soft drink intake among teenagers has been linked to poor-quality diets and excess weight.

That is one reason why a growing number of schools are stocking vending machines with milk instead of soft drinks. Additionally, several states have introduced legislation to limit the availability of soft drinks in schools.

Barr said it is going to take a concerted effort in schools, at home and in communities to reverse the current trend in beverage consumption among today's teenagers.