An overly robust immune response to usually harmless germs has been linked to colitis, a potentially severe inflammation of the colon. A study not only reveals that the presence of one class of fatty acids is the hidden villain that quietly triggers this inflammation, but also found that another group of fats—unsaturated fats such as those found in olive oil—can alleviate symptoms of colitis in mice. The cytokine interleukin-10 (IL-10), part of the innate immune system, is essential for suppressing inflammatory responses in the gut. In fact, children born without IL-10 need bone marrow transplants which can produce the cytokine...