Gas. Bloating. Belching. Diarrhea.

You might be thinking lactose-intolerance or a too-generous helping of beans, but it could be dietary fructose intolerance—a compromised ability to digest the sugar, fructose.

The little known condition is increasingly being diagnosed and treated, thanks in part to Satish Rao, MD, and colleagues associated with University of Iowa Health Care.

“Dietary fructose intolerance has been less known than irritable bowel syndrome,” says Rao, a professor of internal medicine at the UI Roy J. and Lucille Carver College of Medicine and a gastroenterologist with UI Hospitals and Clinics.

“However, for people with gastrointestinal symptoms or those who have already been diagnosed with the syndrome, it is worth raising the question of dietary fructose intolerance.”

Dietary fructose intolerance, while problematic, is not life-threatening and thus different from hereditary fructose intolerance, a rare condition usually identified in childhood.

“Fortunately, we have improved our ability to diagnose people with dietary fructose intolerance and we can suggest dietary changes that might help relieve symptoms,” Rao says.

Fructose occurs naturally in foods, such as apples and pears, and people have been eating it for generations. Today, however, many Americans eat vastly more fructose and in a purer form rather than mixed with other sugars.

The problem is that there is no enzyme in the gut to digest fructose. It requires the presence of an equal amount of another sugar—glucose—to be appropriately absorbed into the small intestine. But some foods have far more fructose than glucose, or no glucose at all, and that spells trouble for some people.

“You need a proper diagnosis because it is not a trivial issue,” Rao says. “If you have fructose intolerance you may want and need to make dietary modifications for the rest of your life.”

While it might be tempting to try making certain modifications on your own, Rao recommends against making major dietary changes if you suspect fructose-intolerance.

“You really need proper education for both diagnosis and treatment, in consultation with a physician and dietitian,” he says.

Rao and colleagues are now studying an enzyme-based therapy that might treat the condition.

—Becky Soglin

“In the past, we ate occasional amounts of fructose in balance with other foods and sugars, but now it is present in many drinks, candy, and canned foods, especially as high fructose corn syrup. If you take it in bits and pieces, it adds up fast.”

—Satish Rao, MD.