Step Aside, Probiotics: This Is The Real Secret To A Healthy Gut

Photo: Guille Faingold

Awareness of the gut microbiota—and its impact on health—has had a profound impact on wellness over the last decade or so. And if you’re like most health-conscience consumers, you’re probably using foods and supplements to support digestion and promote microbial diversity. After all, when it’s all said and done, we all want the friendly microbes in our intestines to thrive and produce healthy benefits.

But as we practice good eating habits to fertilize a healthy gut microbiota, let’s not forget that gut microbes, beneficial or not, are foreigners to our body’s immune system and will elicit inflammation and disease if they aren’t kept at a safe distance. Some gut microbes might be considered "friendly," but that doesn’t mean we want them in places they don’t belong; kind of like your next-door neighbor, they might be friendly, but you don’t want them taking up residence and eating all your food.

When our gut epithelium lining has too much direct contact with gut microbes or their cellular by-products, we can get sick. That’s why we need a healthy barrier to keep the trillions of microbes in our guts at a safe distance. Our bodies accomplish this through something called the colonic mucus barrier.

The colonic mucus barrier allows us to get along with the trillions of microbes living in our gut.

Bear with me as I give a quick lesson on the colonic mucus barrier and how it’s maintained. Understanding a little bit of biology here can go a long way toward implementing strategies that work to build up a strong and healthy personal space between you and your gut microbiota.

The colonic mucus barrier is produced by specialized cells in our gut epithelium lining that secrete mucin. Mucin is a polysaccharide (a type of carbohydrate) that is combined with protein to form a strong, gel-like substance that is tightly adhered to the gut epithelium. The microbes in our intestines do not colonize the tight inner layer of the mucus barrier, but as enzymes that we and our bacteria produce break down the sugar and protein backbones of the barrier, a loose outer layer is formed that supports a diverse population of microbes. Our gut epithelium is constantly producing mucin to replenish the strong inner layer of mucus to keep the gut microbes at a safe distance, while the outer layer gradually breaks down.

Bad things happen when the mucus barrier breaks down faster than our body can replenish it.

It’s important to note that while most bacteria do not utilize mucin as a nutritional source, there exists a distinct group of mucus-degrading microbes that do feed on this substance. These types of bacteria, if not kept in check, can wreak havoc on the colonic mucus barrier. If present in sufficient numbers, they may degrade the mucus barrier faster than the body can replenish it. Without the barrier in place, our personal space is compromised and the gut epithelium is exposed to enteric pathogens, followed by inflammation, infection, and disease.

So, what can be done to prevent your personal space from being destroyed by mucus-degrading bacteria? The answer, not surprisingly, is found in the food that we eat. Researchers recently performed experiments to determine if dietary fiber deprivation can promote mucus-eroding microbiota in laboratory mice. They also wanted to determine if the presence of mucus-eroding microbiota promotes greater susceptibility to pathogens.

To do this, they colonized the intestines of germ-free mice with a synthetic human gut microbiota and exposed the mice to either a plant fiber-free diet or a plant fiber-rich diet. The researchers discovered that during periods of dietary fiber deficiency (in other words: a diet that’s not too dissimilar to a typical nutrient-deficient Western diet), the gut microbiota resorted to breaking down the colonic mucus barrier to obtain nutrients.

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Gut microbes are experts at digesting complex polysaccharides

Compared to our gut microbiota, we humans are novices when it comes to producing digestive enzymes. In fact, we produce a paltry approximately 17 digestive enzymes while our gut microbiota produces thousands of them. Our enzymes are geared toward digesting starches, while the gut microbiota enzymes are highly specialized at digesting the massive variety of polysaccharides contained in dietary fiber. Without our gut microbiota, we don’t properly digest plant-based foods.

When the gut microbiota is starved of their favorite food (dietary fiber), they’ll begin to look for other things to eat, including, it seems, the complex polysaccharide matrix of the colonic mucus barrier. Remember that our gut microbiota has incredible digestive power and an amazing capacity to ramp up production of whatever enzyme to survive.

In the case of the laboratory mice in the study I mentioned before, the fiber-starved, mucus-degrading bacteria of the gut microbiota ramped up the expression of special enzymes that decimated the protective mucus lining of the intestine. Not surprisingly, when the mucus barrier was degraded, susceptibility to enteric pathogens (pathogens that threaten the intestines, specifically) increased. That’s because the protective barrier was lost, and pathogens within the microbiota invaded the gut epithelium.

Nurture your personal space and keep your gut microbes happy with dietary fiber.

We often hear about the health benefits of fiber in our diets. We know, for instance, that fiber normalizes bowel movements by bulking up stools and making them easier to pass. We also know that fiber is digested by the microbes in our gut to produce beneficial by-products such as short-chain fatty acids. Now, scientists are beginning to understand that dietary fiber also supports the integrity of the intestinal lining by preventing the degradation of the colonic mucus barrier.

Unfortunately for those eating the standard American diet, which is low in whole plant foods and high in animal fat, sugar, and salt, fiber deficiency is a chronic condition. The daily recommended fiber intake is between 21 to 25 grams for women and 30 to 38 grams for men. But that’s just the minimum, and many people who adopt poor eating habits fall well short of that amount. In fact, several diseases have been linked to dietary fiber deficiency, and some have hypothesized that the increase in chronic diseases in our modern society can be linked to a deficiency of dietary fiber in Western diets.

The good news is that if you're looking for good sources of fiber, you don’t have to go far because plant-based fiber is abundant and plentiful. These foods, unlike the prepackaged processed foods found on our grocery store shelves, have sustained humans since the beginning of time. They are delicious and, best of all, the tens of trillions of microbes in our intestines find them to be quite satisfying. As an added benefit, our gut microbiota will ferment the polysaccharides contained in these foods to produce nutrients that make us healthy.

  • Vegetables
  • Nuts
  • Berries
  • Oatmeal
  • Beans
  • Grains
  • Popcorn

Recent advances in microbiome science have revealed just how important microorganisms are to our health. We are dependent on them to fight off pathogens and to provide us with essential nutrients. Meanwhile, they are dependent on us to provide nourishment. Based on the study described here, we are wise to consume no less than the daily recommended amount of fiber because it’s possible that certain microbes may take matters into their own hands by invading our personal space and degrading the mucus barrier that is designed to keep us safe.

Ever wondered if you can eat too much fiber? Here's your answer.

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