Fat, Fructose May Contribute to IBS Symptoms

October 14, 2003

Oct. 14, 2003 (Baltimore) — Two new studies exploring the role of diet in irritable bowel syndrome (IBS) suggest that fat and fructose may contribute to symptoms of the gastrointestinal disorder that affects more than 1 in 10 Americans.

One study showed that patients with IBS and fructose intolerance who eliminated fruit and other fructose-rich foods from their diet experienced an improvement in symptoms.

Another study showed that people with functional gastrointestinal disorders, about half of whom had IBS, consumed a diet with a higher proportion of high-fat, low-carbohydrate foods than their healthy counterparts.

Neither study proves cause-and-effect, researchers stressed. But both studies, presented here this week at the 68th annual scientific meeting of the American College of Gastroenterology, point to the need to work with patients to identify possible dietary triggers of gastrointestinal symptoms, they said.

In the first study, Young K. Choi, MD, from the University of Iowa in Iowa City, and colleagues tested 80 patients with suspected IBS; 30 had positive fructose breath tests. The patients were taught to identify foods high in fructose and urged to avoid them.

While not as well known as lactose intolerance, fructose intolerance is common, with previous research by the same investigators showing it affects up to 58% of patients with symptoms of IBS.

After one year, 26 patients were available for a follow-up evaluation that included a structured interview to assess their dietary compliance and symptom patterns. Only 54% of participants reported that they remained on the fructose-restricted diet for a significant amount of time, Dr. Choi reported.

But those who remain on the fructose-restricted program reported significantly less abdominal pain, bloating, and diarrhea than before changing their diets (P < .05), he said. Noncompliant patients showed no improvement in symptoms.

On the ROME I scale, only 43% of patients who complied with the fructose-restricted diet continued to have symptoms of IBS compared with 75% of those who continued to eat fructose-rich foods.

Eleven (79%) of 14 patients who avoided fructose reported a strong correlation between occasional noncompliance and symptoms, the study showed, compared with 1 (8%) of 12 noncompliant patients.

Richard G. Locke, III, MD, associate professor of medicine at the Mayo Clinic in Rochester, Minnesota, questioned whether patients in the study really had IBS. "We used to think people who were intolerant to milk had IBS but now we know they have lactose intolerance," Dr. Locke said. "The same thing could be happening here. It's a matter of labeling."

The important message is to "educate patients that fructose can cause these symptoms," said Yuri A. Saito, MD, MPH, also of the Mayo Clinic. "The general public is not aware of this."

The second study, performed by Dr. Saito and colleagues, from the Division of Gastroenterology and Hepatology at Mayo, enrolled 221 patients, aged 20 to 50 years, about half of whom reported symptoms of functional gastrointestinal disorders on a well-validated self-report bowel disease questionnaire. All of the participants completed the Harvard Food Frequency Questionnaire, and a subset of 53 cases and 58 controls also kept diet diaries for one week.

Of the cases, 46% had IBS, 27% had functional dyspepsia, 20% had both, and the rest had other functional gastrointestinal disorders, Dr. Saito reported.

The Wilcoxon rank sum test showed that patients with functional gastrointestinal disorders reported consuming more fat in their diets: 33.0% of total calories vs. 30.7% for control patients (P < .05). The findings held true for both saturated fat and monounsaturated fat, she said.

Also, carbohydrates accounted for 49.1% of total calories in cases patients compared with 51.9% in control patients (P < .05), the study showed.

No significant differences between the two groups were found for protein, fiber, iron, calcium, niacin, or vitamins B, C, D, or E intake.

Subjects with functional gastrointestinal disease were also significantly more likely to suffer from food allergies than healthy subjects, Dr. Saito reported.

Further studies are needed to determine whether a high-fat, low-carbohydrate diet causes gastrointestinal symptoms or reflects changes that are adaptive, she said.

In the meantime, Dr. Saito said she does not recommend any blanket change in dietary recommendations. Instead, she works with her patients to uncover any foods that make their symptoms worse so they can be eliminated from the diet. "It is important to review my patients' food histories and look for obvious triggers such as excess fructose or sorbitol," she said.

Kevin W. Olden, MD, associate professor of medicine in the Division of Gastroenterology at the Mayo Clinic in Scottsdale, Arizona, agreed. "I advise my patients to eat what they enjoy. If they identify a food that makes them feel sicker, they should not eat that food. But you can't tell everyone not to eat cornflakes." Dr. Olden was not involved with the study.

ACG 68th Annual Scientific Meeting: Abstract 21, presented Oct. 13, 2003; Abstract 547, presented Oct. 14, 2003.

Reviewed by Gary D. Vogin, MD

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