Fiber: it’s not just for “roughage”

I think most of us thought that the value of eating fiber-rich foods was for the roughage it provides—undigestable bulk that keeps food moving through your digestive tract. It turns out that eating fiber is way more important than that. It feeds billions of bacteria in our guts, keeping them happy and, in turn, keeping our intestines and immune systems in good working order.

Here’s how it works: enzymes in our bodies break down food molecules, enabling us to digest the food. But our bodies make a limited range of enzymes, so we can’t break down many of the tough compounds in plants. That’s where the bacteria come in. Hundreds of species of bacteria live atop a layer of mucus that line our intestines. Some of them have the enzymes needed to break down various kinds of fibers—the kind present in vegetables, fruits, and nuts. After they’ve used the fiber for their own purposes, they cast off the leftovers in the form of short-chain fatty acids, which are absorbed by the intestinal cells that use it as fuel. Some of the short-chain fatty acids pass into the bloodstream and travel to other organs, where they act as signals to quiet down the immune system. Intestinal cells also rely on chemical signals from the bacteria to work properly: to make a healthy supply of mucus and to release bacteria-killing molecules when needed.

Scientists have found that diets low in the fiber result in a variety of negative effects. For one thing, certain populations of bacteria crash; many common species become rare and rare species become common. Without a steady stream of chemical signals from bacteria, the intestinal cells slow their production of mucus as well as bacteria-killing poisons, which are needed to wipe out the bacteria that get too close to the gut wall—a condition that kicks the immune system into high gear. In the words of one of the scientists, “The gut is always precariously balanced between trying to contain these organisms and not to overreact.  It could be a tipping point between health and disease.”

I hate to be tiresome, but I'm afraid it's important to eat those fruits and vegetables.

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