Here's an excerpt:
Researchers at the University of Chicago found that concentrated milk fats, which are abundant in processed and confectionary foods, alter the composition of bacteria in the intestines. These changes can disrupt the delicate truce between the immune system and the complex but largely beneficial mix of bacteria in the intestines. The emergence of harmful bacterial strains in this setting can unleash an unregulated tissue-damaging immune response that can be difficult to switch off.
“This is the first plausible mechanism showing step-by-step how Western-style diets contribute to the rapid and ongoing increase in the incidence of inflammatory bowel disease," said study author Eugene B. Chang, MD, PhD, the Martin Boyer Professor of Medicine at the University of Chicago. “We know how certain genetic differences can increase the risk for these diseases, but moving from elevated risk to the development of disease seems to require a second event which may be encountered because of our changing lifestyle."
And here's the article: Western Diet Triggers Colitis in Those at Risk