The condition, also known as fructose malabsorption, is being increasingly diagnosed and treated, thanks in part to research by Satish Rao, M.D., and colleagues at the University of Iowa.
"Dietary fructose intolerance has been less known than irritable bowel syndrome (IBS), a disorder that causes bowel symptoms -- diarrhea or gas and bloating as well as constipation," said Rao, who is professor of internal medicine at the University of Iowa Carver College of Medicine and gastroenterologist with University of Iowa Hospitals and Clinics. "However, for people with gastrointestinal symptoms or those who have already been diagnosed with IBS, it is worth raising the question of dietary fructose intolerance."
Rao noted that dietary fructose intolerance, while problematic, is not life-threatening and thus different from hereditary fructose intolerance, a much rarer condition that is usually identified in childhood. In the hereditary condition, the body lacks an enzyme in the liver to metabolize or breakdown fructose. Consequently, toxic substances accumulate in the body that can seriously harm organs such as the liver and kidneys.
"Fortunately, we have improved our ability to diagnose people with dietary fructose intolerance and, based on this, we can suggest changes in diet that might help relieve their symptoms," Rao said.
Fructose occurs naturally in foods, such as apples and pears, and as Rao pointed out, people have been eating it for generations. However, what has changed in recent decades is that many people in the United States eat vastly more fructose and in a purer form rather than mixed with other sugars. A U.S. Department of Agriculture study estimated that total annual fructose consumption has increased nearly nine-fold -- from less than a ton in 1966 to 8.8 million tons in 2003.
"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, and if you take it in in bits and pieces, it adds up fast," Rao said.
The problem, aside from added carbohydrates to the diet, 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.
Rao's research has improved ways to identify patients with the problem. Research his team published in August 2007 in the journal Clinical Gastroenterology and Hepatology helped establish a standard method for testing for fructose intolerance.
The study verified previous research that showed people without dietary fructose intolerance can typically absorb up to 25 grams of fructose in a serving but that many have malabsorption with 50 grams of the sugar. The researchers also determined that a solution containing the same amount of fructose as another, but in a higher concentration relative to the liquid (33 percent versus 10 percent), was harder for people to absorb. The diagnostic approach can be used at clinics throughout the country.
Patients drink a liquid solution containing fructose, and over a three-hour period have their breath samples collected and analyzed for hydrogen and methane. These gases are produced if fructose is not absorbed in the small bowel and instead ends up in the colon, where it is fermented by bacteria. A significant elevation in breath hydrogen or methane is usually diagnostic of dietary fructose intolerance, Rao said.
Other UI research suggests that up to one-third of people with IBS also have fructose malabsorption. Those findings have been presented by Rao at conferences and published in March 2008 in the Journal of Clinical Gastroenterology.
Once a person is diagnosed, he or she may be able to find some relief through changes in diet. Rao and colleagues have identified foods that can be problematic for those who are fructose-intolerant, as well as alternative food choices. Dietary changes are best made by individuals in consultation with a physician and a dietician.
"You need a proper diagnosis because it is not a trivial issue in the sense that if you have fructose intolerance you may want and need to make dietary modifications for the rest of your life," Rao said. "While a person might want to do a trial of going off certain foods, we don't recommend making major diet changes on your own if you suspect fructose-intolerance. You need proper education for both diagnosis and treatment."
Rao and colleagues are now studying an enzyme-based therapy that might treat the condition.
As with all medical care, it is best to consult with your physician before making any changes to your health care routine.
