Gut health means a thriving microbiome
Credit: Illustration by Neil Web

The New Science of Your Gut: The Real Reason to Eat Fiber

The so-called standard American diet – full of processed foods and carbs, and lacking in vegetables – does little to nourish our microbiome. Our body's good bacteria feed primarily on dietary fiber. In a process similar to the way bacteria turn milk into yogurt or cabbage into sauerkraut, the bugs in our bodies break down the fiber by fermenting it, satisfying their needs and leaving behind organic acids that nourish and repair the cells of the colon. "The old view was that you needed the fiber to keep your bowels regular," says University of Pittsburgh gastroenterologist Dr. Stephen O'Keefe, "but now we know there are much more important reasons." This goes so far as to include cancer prevention: O'Keefe recently published a study linking increased diversity of the gut microbiome with lower colon cancer rates.

Dietary fiber also feeds our best friends in the bug world, like the bifidobacteria and lactobacilli, which help maintain an acidic environment in the gut and are inhospitable to potentially nasty strains of bacteria, yeast, and parasites. When a colon turns more alkaline, these nasty microbes multiply, which can cause chronic symptoms like fatigue and brain fog. The colon walls can also become more permeable when the good bugs aren't well-fed, allowing bits and pieces of bacteria to enter the bloodstream. This is commonly called leaky gut syndrome, and it triggers low-grade inflammation, which is increasingly thought to cause massive problems throughout the body – from heart disease to obesity. Other disturbing scenarios are possible. "One of the things that happen when we eliminate dietary fiber is the bacteria shift over and start eating us," or, more specifically, the lining of our colon, says Sonnenburg, who discovered this phenomenon in lab mice. This may be another way that a bad microbe-human marriage contributes to the inflammation that undermines human health.

It all adds up to more reasons to double down on those vegetables and fruits. The government recommends 38 grams of fiber a day – the equivalent of about seven servings of broccoli. Nutritionist Kathie Madonna Swift, co-author of 'The Inside Tract: Your Good Gut Guide to Great Digestive Health,' suggests starting with a base of eight to 10 servings of veggies and fruits a day, and building on that foundation with servings of legumes, whole grains, and nuts. Sonnenburg also says to load up on vegetables like onions, garlic, and celery, which contain the compound inulin, a preferred food for the bifidobacteria, which in turn feed our colon.