Diet and food components shape the gut microbiome

The gut microbiota is linked to so many aspects of our health, and several recent studies have observed an imbalanced gut microbiota, also called dysbiosis, in conjunction with various non-infectious diseases such as obesity, diabetes, cardiovascular diseases and gastrointestinal disorders such as irritable bowel disease.

Luckily there are tangible ways we can change our gut microbiota composition. Diet has been shown to greatly impact the gut microbiota composition, which consequently also affects the production of beneficial short chain fatty acid production, intestinal barrier function and immune health.

Within the gastrointestinal tract lies crucial aspects to the immune system including the gut-associated lymphoid tissue (GALT) as well as the intestinal barrier that is supposed to maintain proper nutrient absorption while simultaneously keeping foreign invaders out. The GALT is one of the human body’s largest lymphoid organs that contains an estimated 70% of the body’s immune cells such as dendritic cells.

When the function of the intestinal barrier is compromised, large molecules, such as food components and lipopolysaccharides (LPS) which are present on outer cell membrane of Gram negative bacteria, can escape the gastrointestinal tract into the blood stream which triggers an inflammatory immune response including allergies, food intolerances and gastrointestinal disorders.

A review by Rinninella and colleagues in Nutrients discusses how certain diets as well as food components and additives affect the gut microbiota composition.

Compared to a vegan, Western, ketogenic, gluten free and low FODMAP diet, the Mediterranean diet appears to be the gold standard for supporting a healthy gut microbiota composition that promotes high SCFA production because it includes whole foods such as a variety of antioxidant rich plants and vegetables, healthy amounts of monounsaterated and omega 3 fatty acids and includes a balance of all the food groups.

Moreover, long-term elimination diets such as gluten free and ketogenic diets have been shown to decrease bacterial diversity in the gut whereas the Western diet has been shown to be pro-inflammatory.

Food components

Fiber: Bacteria in the colon ferment certain fermentable dietary fiber such as fructo-oligosaccharides (FOS) which result in the production of short chain fatty acids such as butyrate which plays a major role in maintaining proper intestinal barrier and immune function. The amount and types of non-digestible fibers consumed alters the types of bacteria that ferment these fibers as well as the SCFA produced in the colon.

Prebiotics are another type of fiber that serve as food for beneficial bacteria that can also produce SCFA.

Protein

The effects of protein consumption on the gut microbiota appears to depend on whether the protein is animal or plant derived. A high consumption of animal protein could result in the production of more harmful metabolic byproducts from bacteria such as trimethylamine N-oxide (TMAO), which has been associated with cardiovascular diseases. On the other hand, plant protein consumption has been shown to decrease the amount of pathogenic bacteria.

Fat

As with protein, the type of fat consumed also affects the gut microbiota composition. Although a high fat diet could lead to dysbiosis and an impaired intestinal barrier, consuming omega 3 fatty acids and monounsaturated fat like olive oil may exert positive effects on the gut microbiota such as reducing inflammation and increasing SCFA production and the abundance of beneficial bacteria.

On the other hand, a high consumption of inflammatory omega 6 fatty acids and saturated fats, which are consumed in high amounts in a typical Western diet, can promote inflammation and contribute to increased intestinal barrier permeability, also called “leaky gut.”

Omega 3: These polyunsaturated fats are found primarily in fatty fish have been found to increase the levels of beneficial bacteria that produce anti-inflammatory compounds and butyrate.

Omega 9: Also called monounsaturated fat, omega 9 fatty acids found in extra virgin olive oil is not only a staple of the Mediterranean diet but are also associated with higher levels of beneficial bacteria like Bifidobacterium.

Food components and additives

Salt: Consuming a high salt diet may result in an increase in inflammatory bacteria in the gut and decreased SCFA production which may negatively alter gut microbiota composition and immune health.

Artificial sweeteners and emulsifiers: A high consumption of these additives appear to negatively affect the gut microbiota composition leading to dysbiosis and gut inflammation.

Micronutrients

Even though the gut microbiota can synthesize various B vitamins and vitamin K, other micronutrients consumed through the diet can also affect the gut microbiota composition.

For example, vitamin D positively affects gut microbiota composition and also promotes a healthy immune response and intestinal barrier function. The anti-inflammatory effects of the antioxidant beta carotene has also been found to positively affect the gut microbiota by increasing the amount of beneficial bacteria such as bifidobacteria and lactobacilli..

On the other hand, excess zinc and iron status seem to promote the colonization of pathogenic bacteria in the gut such as Clostridium difficile.

Polyphenols

Besides vitamins and minerals, polyphenols found in thousands of plant foods such as fruits, vegetables, herbs, and cacao, promote a greater abundance of beneficial bacteria, and some polyphenols also exert prebiotic activity. Additionally, gut bacteria also positively affect the bioavailability of the beneficial polyphenols so they can exert their health benefits.

Conclusion and Take Away

Unsurprisingly eating a diet high in fiber, fruits, vegetables and omega 3 fatty acids promote a healthy gut and gut microbiota composition. Consuming a Western diet which is high in sugar, salt and food additives can cause a decrease in beneficial bacteria which could increase intestinal permeability and inflammation.

Current studies have provided evidence that the Mediterranean diet to be the most overall beneficial for the gut microbiota because it promotes bacterial diversity and proper intestinal immune and intestinal barrier function. On the other hand, it remains inconclusive as to whether a vegan or vegetarian diet provide long-term benefits for the gut microbiota.

Taking a personalized approach to nutrition keeping in mind the effects diet and food components as well as vitamins, fiber and antioxidants affect the gut microbiota composition and immune health should be considered.

***This aricle was originally written for Gut Microbiota for Health.

Reference: Rinninella E.. et al. Food components and dietary habits: Keys for a healthy gut microbiota composition. Nutrients; 2019: 11, 2393; doi:10.3390/nu11102393. https://www.mdpi.com/2072-6643/11/10/2393