BOSTON (AP) — Rules aimed at banning sugary sodas, sweet snacks, potato chips and other standard school vending machine fare appear to be working in Massachusetts, according to a study released Wednesday.

The study of 74 middle and high schools in three dozen districts showed big increases in the offerings of healthy "competitive foods and beverages" — those items sold in vending machines, school stores, and for fundraisers that "compete" with the sale of school meals.

Before the new rules, just 13 percent of competitive foods would have met the standards at the middle school level. One year after the rule, that number rose to 69 percent, according to the study.

At the high school level, just 28 percent of competitive beverages met the standards before the rules. Compliance jumped to 80 percent one year after the rules.

Researchers cataloged information on thousands of foods, including brand names, packaging, and serving size. The study was conducted over an 18-month period to measure the impact of new state regulations.

Northeastern University associate professor Jessica Hoffman, the study's lead author, said the findings are encouraging.

"For decades competitive foods have not been regulated at the national level, so states have taken it upon themselves to do something," Hoffman said in written statement. "These standards that were put in place in Massachusetts were really exciting because at the time they were some of strictest standards in the whole country."

The rules, which were unanimously approved by the state Public Health Council in 2011, ban foods with artificial sweeteners, trans fats, and caffeine from schools' a la carte lines, vending machines, stores, events and fundraisers.

They also ban fried foods and limit the amount of fat, sodium, and sugar that can be in school foods.

In addition, the regulations require schools to offer unsweetened fruits and vegetables wherever food is sold besides in vending machines, and provide water for free at all times. Breads must be made with whole grain, juices must be 100 percent fruit juice, and flavored milk cannot have more sugar than plain low-fat milk.

Most of the changes took effect in the 2012-2013 school year.

"People in food services really did want to make improvements," Hoffman said. The schools received no financial incentive to make the changes or financial consequences for failing to do so, she noted.

She said the research also shows that schools implementing the healthier food options don't experience financial loss.

Hoffman said that the study demonstrates the feasibility of schools making substantial changes in response to requirements for healthier competitive foods, even in the first year of new standards.

Massachusetts has one of the lowest adult obesity rates of any state, according to statistics from the federal Centers for Disease Control and Prevention.

When Massachusetts approved the ban, health officials said the new standards were a way to help promote children's health and well-being in part by helping students develop a taste for healthy foods that would give them good eating habits as they grow older.

The study was funded by the Robert Wood Johnson Foundation.