So, we evolved to have butyrate suppress our immune reaction. So, should our good bacteria ever get wiped out and bad bacteria take over, our immune system would be able to sense this and go on a rampage and destroy the invaders, and continue rampaging until there were only good bacteria creating butyrate to put the immune system back to sleep. OK, but here’s the critical piece. Here’s why this all matters. What if we don’t eat enough fiber? If we don’t eat enough fiber, then we can’t make enough butyrate. We could have lots of good bacteria, but if we don’t feed them fiber, they can’t make butyrate. Sensing such low levels of butyrate, our body thinks our gut must be filled with bad bacteria and reacts accordingly. Our body can mistake low fiber intake for having a population of bad bacteria in our gut. Our body doesn’t know about processed food; it evolved over millions of years getting massive fiber intake. Even during the Paleolithic period, 100 grams of fiber a day. So, on fiber-deficient Western diets, eating Spam on Wonder Bread, when our body detects low butyrate levels in the gut, it doesn’t think low fiber—as far as our body’s concerned, there’s no such thing as low fiber—it thinks: bad bacteria. For millions of years, low butyrate has meant bad bacteria; so, that’s the signal for our body to go on the inflammatory offensive.