Background: Our previous study on Gulf War (GW) Veterans demonstrated that gastroenteritis during deployment is a risk factor for the development of irritable bowel syndrome (IBS) after deployment. Additionally, we found that Veterans with IBS were more likely to report fatigue, joint pains, general stiffness, and headaches, symptoms that are indistinguishable from GW Illness. The majority of patients with IBS believe that diet plays a significant role in their symptoms. This would suggest that changes in diet should improve IBS and symptoms of GW Illness. Diet is a major factor which change gut bacterial along with gastroenteritis, travel, and stress factors, which are relevant to GW Veterans.

Normal diets contain carbohydrates. FODMAPs (Fermentable Oligo-, Di and Mono-saccharides And Polyols) are poorly digested in intestines. These undigested carbohydrates are fermented in the colon by gut bacteria. Fermentation of these carbohydrates can lead to diarrhea and gas/distension of the colon. Most people do not have symptoms after ingestion of these carbohydrates. However, in patients with IBS, the effect of these carbohydrates is more pronounced and can cause gastrointestinal symptoms. A low FODMAP diet may mediate the effect by (1) by changing the gut bacteria and/or (2) by production of chemicals that influence Veteran's intestines.

A diet low in FODMAP has been shown not only to improve symptoms of IBS, but also cognitive functions and depression; symptoms common in GW illness. A low FODMAP diet has not been tried in GW illness. Our goal is to compare low FODMAPs (modified healthy) to a high FODMAP (typical healthy) diet on Veterans with IBS and symptoms of GW Illness. Both diets will be healthy.

Study: We will conduct a randomized clinical trial to compare low FODMAPs diet to a high FODMAP diet. Both diets will be healthy. There will be 1-week screening period to establish a baseline during which Veterans will continue taking their usual diet. Then, the Veterans will be randomly assigned to receive either low FODMAPs or high FODMAP diet for 3 weeks. To maintain blindness and increase compliance, food will be supplied to the Veterans. Neither the investigators nor the Veterans will know which diet they are receiving. Only the kitchen staff will know which diet the Veteran is receiving. Four weeks after this treatment period, we will follow up with Veterans to assess their IBS symptoms. Changes in IBS symptoms and non-intestinal symptoms (fatigue, joint pains, general stiffness, and headache) will be evaluated before and after the diet period with standardized questionnaires. Additionally, gut bacteria will be assessed before and after the 3-week diet period. This will tell us if improvement in IBS was indeed because of change in gut bacteria by the diet.

We will enroll 68 GW Veterans with IBS and symptoms of GW Illness who were deployed and served in Operation Desert Storm between August 1990 and March 1991.

Study Outcomes: Changes in IBS symptoms, non-intestinal IBS symptoms, quality of life, and gut bacteria will be compared in the Veterans who received the low FODMAP diet to the high FODMAP diet.

Conclusion: This study will inform us whether the low FODMAP diet is effective in the treatment of IBS with Gulf War Illness. If this study is successful, we will conduct a future long-term trial to show whether advice about low FODMAP diet alone is effective in large number of Veterans.