by Carol Milano

We all know we need to eat our fruits and vegetables. Yet those healthy apples, peaches, pears, tomatoes and oranges may be a cause of a little-known problem, called fructose intolerance. This is an inability of the body to properly digest fructose, a naturally sweet carbohydrate found in many fruits. The problem is more common in women, and may be mistaken for other medical problems or food intolerances.

With fewer calories and lower cost than sugar, fructose is becoming more common in Western diets. Manufacturers are beginning to use it in many canned foods-- including fruits, juices, vegetables, soups, sodas and corn syrup--as well as some cooked foods sold in stores. It's sometimes listed on nutritional labels, yet few people know much about fructose. Unfortunately, "industry doesn't understand that, while you can eat any amount of table sugar without a problem, humans have limited ability to absorb fructose," reports Satish Rao, MD, PhD, a professor of internal medicine at the University of Iowa College of Medicine in Ames. "Twenty five grams is the limit most people can handle. If you can't absorb that quantity, you're fructose intolerant."

How can you tell if you're in that category? Women with this condition experience problems ranging from bloating and abdominal pain or tension to gas, excess belching and diarrhea. Since incorrect diagnoses are common when symptoms are this general, "it is very important for people experiencing them to speak with their physician so the condition can be accurately tested and diagnosed," advises Dr. Rao, a gastroenterologist who sees patients with these difficulties.

However, fructose intolerance is still little-known among physicians: Dr. Rao estimates that perhaps 5% of gastroenterologists and an even smaller segment of internists are familiar with the condition. His team discovered it because the University of Iowa, a major referral center, sees many patients with unexplained symptoms. Investigating possible causes, their initial study of 80 patients who had been diagnosed with irritable bowel syndrome found that for 30%, their symptoms were actually caused by fructose intolerance. "When we put them on a fructose-restricted diet, we found, anecdotally, that most improved," says Dr. Rao.

Reducing fructose intake may involve some lifestyle change. "Because Western diets contain so much fructose, it can be difficult for people to adjust. Modification will have an impact on what you buy and what you cook for your family," he finds.

Their second study followed 30 fructose-intolerant patients for a year to check their compliance with the recommended diet. Dr. Rao's team found that the 60% who complied had an improvement of nearly 80% in their symptoms; the other 40% had no improvement. "Patients rated their changes in lifestyle, shopping habits, and diet on a one to five scale; the average was three. Patients willing to pay the price got a lot better," he notes.

Dr. Rao's group recently developed the first clinical test for fructose intolerance. The simple, painless breath test requires drinking a sugar solution, then exhaling into a bag every half hour for three hours. The contents, analyzed by a lab, detect most malabsorption. (Insurance coverage is usually available for diagnostic breath tests, though not specifically for the fructose intolerance test.)

Now that Dr. Rao and his colleagues have begun presenting their findings at medical conferences and in journals, the specialist believes more physicians are beginning to understand fructose intolerance. "When they can recognize the symptoms and put the patient on a diet that helps her, that's the first step," he says.

Note: some pediatricians are familiar with a different type of fructose intolerance, caused by an enzyme that is lacking in a child's liver. This very serious condition (often fatal) is inherited, and diagnosed through a liver biopsy.

Dr. Rao's research was published in the American Journal of Gastroenterology 2002;97:S273

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