Both weight and risk for diabetes are lower for people in communities where fast food prices increased.

A new study, reported in the journal Archives of Internal Medicine , also showed when prices fell, consumption, weight, and diabetes risks rose.

"These results indicate that increasing the price of fast foods and sodas can affect adult behavior, and steer them toward healthier diets, lower weight and less risk of diabetes," says senior author Barry Popkin, the Carla Smith Chamblee Distinguished Professor of Nutrition at the University of North Carolina at Chapel Hill.

"This study gives us strong scientific evidence that price policies, including taxes, could actually be effective at helping control obesity and the resulting chronic diseases, like diabetes," Popkin says. "Our results provide robust evidence to support the potential health benefits of taxing selected foods and beverages as a way of improving public health."

Popkin and his colleagues used data from more than 5,000 participants in the Coronary Artery Risk Development in Young Adults (CARDIA) study. When it started in 1985, CARDIA participants lived in four U.S. cities. In the intervening years, they have moved to 48 states.

Researchers collected information on the average prices of products, including restaurant pizza, burgers, soft drinks and whole milk in the counties in which each participant lived. Prices were adjusted to 2006 levels.

When researchers analyzed the diet, weight, and insulin levels of study participants, they found that when prices of fast foods and soft drinks went up just ten percent, participants consumed on average 7.1 percent fewer calories from soda pop and 11.5 percent fewer calories from pizza. That translates to about 56 calories a day less, which corresponds to a reduction of about 3 to 4 pounds a year per person, Popkin notes.

Those who found their fast food prices rose also gained less weight and had a lower risk for diabetes based on a test for fasting insulin.

Taxation, particularly in the form of an excise tax, could be helpful as such measures were successful in the case of smoking cessation efforts, Popkin says. "For these fast foods, taxes would represent the most effective way to reduce adult obesity that we have today, based on this research," he adds.

Popkin also notes that cigarette taxes have been found to have a much larger effect on teenage versus adult smoking and he would expect that fast food taxes on children and teens would similarly have a larger effect than on adults.

Taxes have been proposed on fast foods and soft drinks in some areas, including Detroit . In a number of countries, including Denmark and others in Europe, they are used to discourage consumption and encourage healthy diets.