Soft drink makers should invent and market a new category of semi-sweet beverages that will help wean Americans off their reliance on sugary drinks, nutrition experts said on Monday.

They proposed a new class of reduced-calorie beverages with no more than 1 gram of sugar per ounce, which with about 50 calories is about 70 percent less sugar than a typical soft drink contains. They said such drinks should also be free of artificial sweeteners such as aspartame and saccharine.

"We need to retrain American tastes away from super-sweet drinks," Lilian Cheung of the Harvard School of Public Health said in a statement.

"If we can shift the present American norm back to a lower expectation of sweetness, people will adjust their palates, particularly the younger population."

The American Beverage Association, which represents soft drink makers, was not immediately available for comment.

The researchers cited evidence that sugary drinks are an important contributor to the epidemic of obesity and type 2 diabetes in the United States, where more than two-thirds of the population is overweight or obese.

"The scientific evidence is now clear; soda and other sugar-sweetened beverages are important contributors to obesity in children and adults," said Walter Willett, chairman of Harvard's Department of Nutrition.

"Healthier beverage options would allow individuals to make better choices."

The group said four out of five children and two out of three adults drink sugar-sweetened beverages on any average day. A 20-ounce (590 ml) bottle of soda contains nearly 17 teaspoons (255 ml) of sugar and 250 calories (1.05 kj) and they said the Food and Drug Administration should be empowered to require more detailed labeling.

In a study of 90,000 women published in the April issue of the American Journal of Clinical Nutrition, the Harvard team reported that women who drank more than two servings of sugary beverages each day had a nearly 40 percent higher risk of heart disease than women who rarely drank such drinks.

Food and beverage makers blame a lack of exercise and say people can choose to responsibly eat snack foods.