The number of people with type 2 diabetes is rising and the associated costs are spiraling out of control. In the U.S. alone, about 29 million adults — one in 11 — have type 2 diabetes.

And one in three Americans have pre-diabetes, blood glucose levels that are higher than normal but not yet high enough to be diagnosed as diabetes. But pre-diabetics are at a higher risk for developing type 2 diabetes and cardiovascular disease.

Foods sweetened with high fructose corn syrup have long been seen as major culprits behind rising rates of obesity and diabetes. Now a new study challenges the current dietary guidelines, which say up to 25 percent of daily caloric intake can come from added sugars containing fructose.

A new study challenges the current dietary guidelines.

People should be eating less sugar, the researchers say, a lot less.

The researchers examined data from 125 studies. Consuming foods high in added fructose causes metabolic disturbances and insulin resistance, they found. But dietary sugars without fructose, such as glucose and starch, do not have these effects.

A growing body of evidence suggests that fructose, in the form of added high-fructose corn syrup or table sugar, is becoming a serious public health issue. The researchers advise Americans to reduce their sugar intake, even if highly-regarded organizations say otherwise.

“We do not suggest going with the Institute of Medicine guidelines, which say that up to 25 percent of total daily calories can come from added sugars,” James DiNicolantonio, lead author on the study, told TheDoctor. Even consuming about 15 percent of daily calories from added sugars has been associated with metabolic harm.

By contrast, the World Health Organization guidelines advise that between five and 10 percent of daily calories can come from sugar, with five percent the recommended level for optimal health, said DiNicolantonio, a cardiovascular research scientist at Saint Luke’s Mid America Heart Institute.

You should limit your total sugar intake to 40 grams or less per day, he adds. This recommendation is in line with those of the American Heart Association, which says that women should have no more that 24 grams (six tablespoons, about 100 calories) of sugar per day and men no more than 36 grams (nine tablespoons, about 150 calories).

The best way to avoid having too much sugar is to eat whole foods, said DiNicolantonio. Fruits and vegetables contain sugar, but in less concentrated amounts than in processed foods, and they also contain water, fiber, antioxidants, and other nutrients your body needs.

If you use sugar in your coffee, don't. Instead, maybe follow DiNicolantonio, who doesn’t add sweetener to his coffee, just cream, which actually makes the coffee taste a little sweet. You can use sugar or honey, but no more than two packets of sugar. DiNicolantonio is not a fan of agave nectar because it is about 90 percent fructose.

The study is published in Mayo Clinic Proceedings.