Primary adult lactose intolerance protects against development of inflammatory bowel disease.

We have compared the incidence of inflammatory bowel disease (IBD) to the prevalence of lactose malabsorption (LM) in several countries. Our observations indicate that IBD is rare where LM is highly prevalent. The correlation between incidence of Crohn's disease and LM is -0.93, p less than 0.01, the correlation between incidence of ulcerative colitis and LM is -0.89, p less than 0.01. We, therefore, propose that LM results in the formation of volatile fatty acids which may inhibit multiplication of potentially pathogenic organisms.