Irritable bowel syndrome (IBS) is a chronic gastrointestinal illness of unknown cause whose symptoms include abdominal pain, bloating and altered bowel pattern. Diet has been shown to influence the bacteria gut interaction. Our aim is to determine if components of the diet affect IBS symptoms by changing the bacteria gut interaction. In particular, we will measure whether after being on a diet high or low on certain factors there is a change in the timing and amount of hydrogen and methane produced by bacteria digesting lactulose and on IBS symptom severity.

Inclusion Criteria:

• Meet Rome III criteria for IBS
• Willing to undergo dietary intervention

Exclusion Criteria:

• History of Gastric, Small Bowel or Colonic Surgery
• History of Inflammatory Bowel Disease
• Celiac Disease
• Unable to come off following medications: antibiotics, laxatives, narcotics, sedatives
• On a pre specified diet
• Pregnant