The bacteria that live in your gut are key to your good health. You want to encourage the beneficial ones and crowd out the harmful ones. How exactly can you do that? A healthy diet with minimal sugar and processed foods encourages the good bacteria; so, do probiotic supplements. But just as important—possibly more so—is eating foods high in insoluble fiber. That means eating a diet high in plant-based foods.
Fiber is usually defined as the parts of plant foods that can’t be digested by the human digestive tract. Its usually broken down into two categories: soluble fiber and insoluble fiber. Soluble fiber attracts water and turns into a soft gel during digestion. Soluble fiber is found in beans, lentils, peas, barley, oatmeal, nuts, seeds, and some fruits (apples and peaches, for example).
Insoluble fiber is made up mostly of tough plant cell walls that don’t absorb water. It’s found in whole grains, nuts, and fruits and vegetables. We generally think of insoluble fiber as the plant material that adds bulk to the stool and helps to keep food moving through the digestive tract. Because you don’t digest it, insoluble fiber doesn’t add any calories to your intake.
Insoluble fiber turns out to be more digestible than we thought. It still mostly passes through you unchanged, but it has another key role in your body: It’s food for your beneficial bacteria.
Insoluble Fiber for a Health Gut
Insoluble fiber in your gut is like fertilizer for your beneficial bacteria. Here’s how it works:
When the trillions of bacteria in your gut encounter insoluble fiber from your diet, they get to work fermenting it. That means they use metabolic processes to convert the carbohydrates in the fiber into short-chain fatty acids (SCFAs), mostly butyrate, propionate, and acetate.
SCFAs impact your health in several important ways. In the gut, they help form a strong barrier and prevent leaky gut syndrome. They also inhibit the growth of some unfriendly bacteria. SCFAs could also protect you against intestinal inflammation and colorectal cancer through their effects on your immune system. It’s also possible that SCFAs play a role in appetite regulation and how your body produces energy.
Most importantly, SCFAs are fuel for beneficial bacteria. If your diet is high in insoluble fiber, you’re giving your beneficial bacteria the environment they like best.
Prebiotics in Food
When you want to improve your intestinal flora, a better diet and taking probiotics are important first steps. To get the most benefit from both, however, you also need to add more insoluble fiber to help the probiotic bacteria get established. Prebiotics, as this type of fiber is also known, act as food for the beneficial gut bacteria and stimulate their growth.
To be most effective, a prebiotic need to be insoluble fiber that resists digestion in the stomach and small intestine and reaches the bacteria of the colon largely unchanged.
Prebiotic supplements are available, but the best way to feed your bacteria is simply to eat foods that are high in insoluble fiber. The more fiber you eat, the more SCFAs you produce. The source of the insoluble fiber doesn’t seem to matter as much as the quantity.
According to the National Academy of Sciences, the standard recommendation for dietary fiber is 30 to 38 grams a day for men and 25 grams a day for women. Another way of looking at this is getting 14 grams of fiber for every thousand calories in your diet. In practice, few people achieve the recommended amounts. The median fiber intake for men is actually only 16 to 18 grams a day; for women, it’s only 12 to 15 grams a day.
Many experts now feel the recommended fiber amounts are too low. They recommend 50 grams a day. That might seem like a lot of fiber to consume, but in a diet that’s largely plant-based, it’s not hard to achieve. Following the Mediterranean diet, for example, will give most people at least the recommended amounts and probably more due to the emphasis on fruits, vegetables, and beans and the relatively low intake of red meat and dairy foods.
Foods that are high in oligosaccharides (simple carbohydrates) are particularly good as prebiotics. They’re found naturally in a lot of plant foods, including almonds, asparagus, avocado, barley, berries, cabbage, cherries, chia seeds, chickpeas, coconut, garlic, greens, Jerusalem artichoke, lentils, onions, peaches, pistachios, and walnuts.
Eating your prebiotics is always a good idea—aside from the prebiotic benefit, foods high in oligosaccharides are also high in other valuable nutrients, like omega-3 fatty acids and B vitamins. But sometimes your gut flora need more prebiotics than you can comfortably eat. Supplements can be very helpful.
Prebiotic supplements that contain maltose in the form of isomalto-oligosaccharides (IMOs) are a good choice. This form is found naturally in barley, whole grains, miso, soy sauce, and starchy vegetables. Other oligosaccharides, such as inulin (found in chicory root), acacia, and marshmallow are also used in prebiotic supplements. Unpasteurized apple cider vinegar is also sometimes recommended as a prebiotic.
By eating a diet that’s higher in plants and lower in processed foods, meat, and dairy foods you can restore and maintain your gut bacteria in a way that’s simple, drug-free, and delicious.
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