Diet can have a dramatic effect on our gut bacteria. A powerful antibiotic like Cipro can take a week to shift our microbiome, but if we eat a diet heavy in meat and eggs, we can change our microbiome within a single day—and not for the better. Eating animal products can result in toxic metabolites, such as an increase in levels of deoxycholic acid, which can promote DNA damage and liver cancers. The amount of bad bacteria that we have that produce deoxycholic acid triples in only two days after switching to a diet based on animal products. Over time, the richness of the microbial diversity in our gut may disappear. We have a hundred trillion microorganisms living in our gut. The symbionts—the good bacteria that live in symbiosis with us—are largely nourished by fruits, vegetables, whole grains, and beans. Pathobionts—the disease-causing bacteria that may disrupt our microbial balance—instead appear to be fed by meat, dairy, eggs, junk food, and fast food. What we eat determines wha...