Can Insufficient Fiber Intake affect the Gut Microbiome?
Dietary fiber plays an important role in the regulation of the digestive tract, and while the additional benefits of fiber are becoming better known lately, studies link people that eat more fiber with living longer, healthier lives1 and with lower risks for many chronic diseases.
Fibers are also gaining an increased understanding, as it relates to the microbiome. While we’re well aware that providing the gut with probiotics is important, we’re now developing an understanding about how dietary fiber feeds these microorganisms within the intestine - which impacts both the number and the diversity of the bacterial species.
What does fiber do to our body?
Fibers are only found in plant foods. It’s a non-digestible complex carbohydrate that helps the body in many ways. Beyond its well-known role of “keeping things moving”, it can help to keep you feeling full longer after eating, lower blood cholesterol levels, balance blood sugar levels, as well as prevent constipation and diverticulosis. The fiber conversation has been getting even more interesting, as it’s beginning to show links between how the intestinal microbiome affects inflammation within the body.
The Two Types of Fibers
There are two types of fiber, soluble and insoluble - both are important!
Insoluble fiber is found in vegetables, in some types of dietary fiber foods such as fruits and whole grains, and is the type of fiber that doesn’t dissolve in water. It helps to keep your bowels working regularly.
On the other hand, soluble fiber is responsible for lowering cholesterol, by binding with fat and cholesterol, and eliminating it via stools, while also contributing to managing glucose levels, by slowing down the digestion of carbs. It’s found in foods like legumes, oat bran, nuts, and seeds and it’s the type of fiber that when dissolved in water, forms a gelatinous substance that lubricates the lining of the gut, which may also help with mineral absorption.
Another important aspect of soluble fiber is that its composition contains ‘prebiotic’ compounds, which allow for it to be broken down and fermented by the microorganisms found in the colon. These compounds, which include inulin and other carbohydrate chains (oligosaccharides, fructooligosaccharides, galactooligosaccharides) act as a food source to the ‘probiotic’ (good) bacteria.
Fiber, the Microbiome, and Inflammation
Along with the discovery of prebiotics came the important realization that prebiotic fiber can have a positive impact on the bacterial diversity in the gut. This is because the more beneficial bacteria that exist inside our intestinal wall, the thicker the gut mucosal barrier protecting the inner body and bacteria from the outside world gets. When the mucus barrier lining is healthy and filled with a plethora of good bacteria, the body has the potential to become protected from unwanted inflammation and avoid complications from problems like ‘Leaky Gut Syndrome’.
Beyond this, when healthy bacteria break down the prebiotic fibers, the resulting products of digestion (short-chain fatty acids) have the potential to circulate anti-inflammation signals2 throughout the bloodstream. This is all very important considering that inflammation lies at the heart of all chronic disease.
The Gut Microbiome Diet
It’s clear that eating prebiotics can influence health in a profound way by increasing the number and type of good microbes. But, the thing is that most of us aren’t getting enough of what we need when it comes to fiber in general. According to the Canadian food guide, Canadian women need 25g of fiber/day where men need 38g/day, while most Canadians are only getting about half that much.3
When it comes to feeding your gut, the best approach is to ensure that there is a variety of natural, gut-loving probiotic-rich foods in addition to a vast variety of fiber-rich, and plant-based foods. This will ensure plenty of good bacteria (probiotics), along with plenty of fuel (prebiotics) to keep the microbiome thriving! Eating seasonal, fresh, unprocessed, whole foods are also good food guidelines to keep in mind as well.
Probiotic-rich foods that’ll enhance the good bacteria in the gut include cultured veggies, kombucha, yogurt, tempeh, and miso. On the other hand, the best prebiotic fuel for the probiotics includes chicory root, garlic, leeks, onions, asparagus, dandelion greens, wheat bran, oats, barley, bananas, and Jerusalem artichokes. Although these are considered as some of the best foods, it’s still important to point out how essential variety is for microbiome diversity, as different types of dietary fibers do feed different strains of bacteria (along with playing other important roles in the body). Furthermore, just as we know that eating a low fiber diet is detrimental, eating the same type of fiber (or taking the same fiber supplement) which feeds the same microbes over time can compromise the gut microbiome as well.
Paying attention to diet has a big impact on your gut microbiome, and to keep it simple, pair a high-quality probiotic that delivers research-backed bacteria into the gut, along with eating a variety of plant-based fibers to feed the bacteria. Perform these two simple steps and you'll surely reap the positive effects of a healthy microbiome on your overall health and wellbeing.
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1. Kim and Je. 2014. Dietary Fiber Intake and Total Mortality: A Meta-Analysis of Prospective Cohort Studies. American Journal of Epidemiology. Vol. 180, No. 6
2. Zou et al. 2018. Fiber-Mediated Nourishment of Gut Microbiota Protects against Diet-Induced Obesity by Restoring IL-22-Mediated Colonic Health. Cell Host & Microbe 23, 41–53
3. Government of Canada. Fiber. Date modified January 22nd 2019: https://www.canada.ca/en/health-canada/services/nutrients/fibre.html