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Can Fiber Help Your Microbiome?

What is fiber? Why is it such a crucial nutrient for people with diabetes and how can it help your microbiome?

Fiber is a critical component of any diet, but unfortunately, most Americans don’t consume enough fiber. While you may know that fiber keeps you regular, you may not realize how many other health benefits it offers. Fiber can be a valuable tool for reducing your risk of diabetes, cardiovascular disease, cancer, and more.

As scientists explore how and why fiber is so good for you, they have uncovered a link between the human digestive tract and the countless microscopic organisms, known as the microbiome, living there. Recent studies suggest that people with type 2 diabetes can actually increase their microbiome diversity and manage their symptoms by eating more fiber.

What is dietary fiber?

Carbohydrates are an important fuel source for your body, and dietary fibers (or “fiber” as most people call it) are types of complex carbohydrates that come in many different categories and may have different effects depending on what type of fiber it is. Complex carbs are largely digested and absorbed by your body and include the starch and fiber found in whole grains, legumes, vegetables, and more.

When you eat complex carbohydrates, your body is able to digest the starch but not the fiber. That sounds bad, but it’s not! The fiber comes in two forms soluble and insoluble. Soluble fiber is fermented and the products are used to send signals all over your body. Insoluble fiber passes through your digestive tract and makes up the bulk of your stool – maintaining regular bowel movements and preventing constipation. Fruits, vegetables, beans and legumes, nuts, whole grains, and potatoes are all good sources of fiber.

Fiber promotes good health

Fiber is a critical component of a healthy diet, but most Americans consume less than the recommended amount of fiber. Because fiber offers so many health benefits, people who eat a low-fiber diet miss out on those perks. 

One of those perks is that diets high in fiber help with weight management. High-fiber foods often have few calories while still being filling. Because your body cannot digest fiber, high-fiber foods move slowly through your stomach and digestive tract, which makes you feel full and can prevent overeating.

By slowing the movement of food through your digestive tract, fiber also slows the digestion of carbohydrates which can help prevent spikes in blood sugar, only increasing your glucose slowly. Consuming indigestible fiber also reduces your risk of colon cancer and lowers cholesterol levels. Finally, fiber consumption reduces chronic systemic inflammation, which contributes to the development of many conditions including cardiovascular disease, cancer, diabetes, chronic kidney disease, and liver disease, as well as autoimmune and neurodegenerative disorders

Fiber benefits people with diabetes

Anyone can benefit from increased fiber consumption, but fiber may help people living with diabetes better manage their condition. It can help you improve digestion, manage your glucose, and lower your cholesterol and risk for heart disease. Plus it may even help promote weight loss and research shows that people who lose 5% or more of their body weight have better glycemic control and may be able to reduce their use of diabetes medication.

Fiber also reduces chronic systemic inflammation, which is a risk factor for diabetes. Plus, new research shows that fiber may also benefit people with diabetes by increasing their microbiome diversity.

What is the microbiome? Why is it important?

The gut microbiome is the set of microscopic organisms that inhabit your gut. You might not realize it, but your digestive tract is teeming with bacteria, fungi, protozoa, and viruses. We tend to think of all these bacteria and other microbes as invaders that make us sick, but most of these tiny organisms help us instead.

Gut bacteria reduce inflammation and seal the intestines, creating a barrier between the intestinal contents and the bloodstream. This barrier prevents disease-causing bacteria and inflammatory molecules from passing from the gut into the body. Having a greater total number of bacteria and other microbes and a diverse array of species promotes health and may specifically help people with diabetes.

To learn more about the microbiome and how it relates to your diabetes, check out diaTribe’s article on the subject, “What is the Gut Microbiome and How Does it Relate to Diabetes?

How diet affects the microbiome 

Since these bacteria live in your gut, it’s not surprising that what you eat directly impacts them. Emily del Conte, a registered dietitian and Certified Diabetes Care and Education Specialist with Evolution, says that “Fiber acts as the food for different bacteria in your gut…trying to give your body a variety of foods with fiber may help [increase] the diversity of bacteria in your gut.”

Certain bacteria feed on fiber, and these are the ones that promote good health by sealing the gut and reducing inflammation. When you eat fiber, these beneficial species increase, crowding out less beneficial ones as well as pathogenic (disease-causing) species. In contrast, when your diet is low in fiber, these less beneficial bacteria grow instead.

Today, the typical Western diet is high in animal fat and protein but low in fiber. In contrast, high-fiber diets that are low in red meat and unsaturated fat, such as the Mediterranean, vegetarian, and vegan diets, increase both the diversity of bacteria in your gut and the growth of beneficial species.

Eating fiber increases gut bacteria diversity in people with type 2 diabetes

Recent studies show that people with type 2 diabetes who eat fiber experience increased microbial diversity and improved health measures. Here are some results showing that people living with type 2 diabetes can improve their gut health and manage their diabetes by increasing fiber consumption:

  • Mediterranean diet: Subjects who followed a low-fat Mediterranean diet for six months improved the total diversity of their gut bacteria, promoted growth of three beneficial species, reduced growth of two pathogenic species, and improved FBG and A1C.

  • Traditional Chinese diet: Subjects who followed a high-fiber diet incorporating fruits, vegetables, nuts, whole grains, traditional Chinese medicinal foods, and prebiotics for 12 weeks improved total gut bacteria diversity, promoted growth of two beneficial species, reduced growth of two pathogenic species, and improved FBG and A1C.

  • Macrobiotic diet: Subjects who followed a macrobiotic diet of whole grains, legumes, vegetables, and roasted green tea improved total gut bacteria diversity, promoted growth of one beneficial species, reduced growth of one pathogenic species, and improved FBG and lowered CRP, a measure of systemic inflammation.

  • Fiber supplements: Studies show that fiber supplements may help at large doses, but not as much as naturally occurring fiber.

Each of these studies focused on a different type of high-fiber diet, and all improved diversity of gut bacteria as well as diabetes-related health measures. The takeaway message is that there is no single diet for improving gut health; any diet that increases fiber consumption, especially through food versus supplements, can help.

How to improve your gut microbiome

Whether you have prediabetes, type 2 diabetes, or just want to improve your health, you can take specific steps to improve your gut microbiome. When you feed yourself, you feed the microorganisms in your gut. Increasing your fiber consumption increases the total number of microorganisms in your gut, the number of distinct species living there, and the number of beneficial species, all while reducing the presence of pathogenic species.

The best way to increase your fiber consumption is to eat more foods that are naturally high in fiber. People with diabetes should focus on lower-carb foods (or foods with complex carbs) to avoid spikes in blood sugar. Here are some good choices of complex-carb, high fiber foods:

  • Beans: Try pintos, lentils, and chickpeas on salads, in soups, or in dips and spreads like hummus.

  • Whole grains: Quinoa, brown rice, and wild rice work well as a base for beans, served cold in salads, or hot in soups.

  • Vegetables: Fresh or cooked veggies that grow above the ground are great but be mindful when eating higher-starch veggies like corn and carrots.

  • Fruit: Fruit is high in fiber but can also be high in sugar, so keep portions small and choose fruits that are low in sugar like berries, peaches, and apples.

  • Nuts and seeds: Peanuts, tree nuts, and seeds are great choices for snacking, on salads, or pureed into spreads.

This article is part of a series on nutrition to support people with diabetes, funded in part by The Ella Fitzgerald Charitable Foundation.