Do you know what your child drank in school today? Probably not something as nutritious as you’d like.

Childhood obesity has increased 20 percent in three decades and while unhealthy foods and decreased exercise are often seen as the main culprits, unhealthy beverages are a calorie-loaded missing link.

A new study from the Archives of Pediatric and Adolescent Medicine found that in spite of guidelines prohibiting unhealthy drinks from being served in school lunch programs, elementary school students across the country still had access to unhealthy beverages from competing vendors.

The three-year study, which tracked school years 2007, 2008 and 2009, included questionnaires sent out to public and private elementary schools across the country. The questionnaires, which asked food-service employees to identify the types of beverages sold through vending machines, stores, a la carte menus and lunch programs were completed by nearly 3,000 schools. Questionnaires also tracked children’s ages, weight and races.

The study found that unhealthy drink options were widely available from a number of sources. Students could purchase high-fat milk and high-sugar sodas or sports drinks from vending machines, snack bars and stores.

Over the three years of the study, an average of 75 percent of public school students had access to high fat milk. Vending machines constituted the most likely place to find an unhealthy beverage. Public schools, and particularly those in the northeast and Southern U.S., had the highest availability of unhealthy drinks.

One positive finding was that the number of students who had access to “healthy” beverages allowed by national health regulations, such as low-fat milk, bottled water and 100 percent fruit juice increased slightly.

Watching beverage intake is important because fat- and sugar-filled drinks can be a hidden source of empty calories without feelings of fullness, which causes people to surpass their daily calorie limits and gain weight.

A 12 oz. can of Coca Cola contains 140 calories. Drinking two cans of soda per day without exercising or proper diet to balance those extra calories can lead to a weight gain of more than two lbs. per month.

Researchers recommend that unhealthy drink options be eliminated from schools and replaced with low-fat milk, water and 100 percent juice.