Are people with irritable bowel syndrome (IBS) more sensitive to certain foods than other people? And if so, what are those foods?

Science doesn't yet have an indisputable answer to that question. But a report in July's American Journal of Gastroenterology may provide more insight.

IBS is a functional condition of the intestine. While no one fully understands what causes IBS, it is not an anatomic problem. According to the American Academy of Gastroenterology, IBS patients have changes in bowel habits, such as constipation or diarrhea. They also have abdominal pain along with other symptoms including abdominal bloating and rectal urgency with diarrhea.

Researchers tested 16 common foods on blood from 132 IBS patients and 43 people without IBS.

IBS patients had higher levels of an antibody called IgG4 in response to five foods, compared with those without IBS. Those five foods were wheat, beef, lamb, pork, and soybeans.

Antibodies are proteins made by the immune system to help fight infections.

IgG is the major antibody in the body; another antibody called IgE is normally present in only trace amounts, but it is responsible for the symptoms of allergy.

However, the study doesn't prove that the five foods caused IBS.

IBS symptom severity and frequency weren't linked to antibody levels, write the researchers. They included Sameer Zar, MRCP, of St. Georges Hospital Medical School in London.

Read WebMD's "Understanding Irritable Bowel Syndrome"

Food Sensitivity

Between one-fifth and two-thirds of IBS patients attribute their symptoms to food hypersensitivity.

By comparison, only about 5 percent of the general population claims food hypersensitivity.

Sameer Zar, MRCP, and colleagues cite those statistics in their report.

Food Test

Zar's study included 52 people with diarrhea-prominent IBS, 32 with constipation-prominent IBS, and 24 with alternating IBS.

Most subjects (91) were women. Average age ranged from 35 to about 43.

Foods tested included milk, egg white, egg yolk, cheddar cheese, rice, yeast, potato, peanut, cod fish, chicken, lamb, beef, pork, tomatoes, and soybean.

Read WebMD's "Quick Quiz: Could You Have IBS?"

Study's Results

Those with diarrhea-prominent IBS had markedly higher levels of the antibody IgG4 for wheat, beef, pork, and soybean.

Those with constipation-prominent IBS had markedly higher IgG4 levels for wheat, lamb, beef, and pork.

Those with alternating IBS had markedly higher IgG4 levels for wheat, beef, and pork.

There was a large variability in the IgG4 antibody level to different food groups, write the researchers.

Skin Prick Test

Skin prick tests were done on a smaller group of participants -- 56 with IBS and five without IBS.

A skin prick test places a small amount of substance that triggers an allergic reaction into the skin. People with allergies to the specific substance have swelling in the injected region of the skin, a reaction caused by IgE antibodies.

A lot of participants didn't take the skin test, which required a separate visit to another center. Due to the low turnout, the test was dropped later on.

Five IBS patients had a positive skin test response to shrimp. So did one person without IBS.

The skin test results didn't sync up with results from the blood antibody tests, write the researchers.

Read WebMD's "Newly Diagnosed with Irritable Bowel Syndrome? Start Here"

Food Journal, Doctors May Help

"For many people, careful eating reduces IBS symptoms," says the National Institutes of Health (NIH).

"Before changing your diet, keep a journal noting the foods that seem to cause distress. Then discuss your findings with your doctor. You may also want to consult a registered dietitian, who can help you make changes to your diet," says the NIH.

By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: Zar, S. American Journal of Gastroenterology, July 2005; vol 100: pp 1550-1557. WebMD Public Information from the National Institutes of Health: "Irritable Bowel Syndrome." National Cancer Institute. American Academy of Allergy Asthma and Immunology. American Academy of Gastroenterology.