Gut Health Series Post #2 - Gut Health and the Immune System
It is a key time to learn more about how our gut microbiota and the health of the gut influence the immune system, especially as summer winds down and fall and winter approach during this continuing pandemic. Achieving and maintaining an optimal balance of healthy and good gut bacteria can help protect us from infections and illness. As stated in the previous blog post regarding the importance of gut health, about 70-75% of the immune system lives within our gut.
The gut microbiota, which is the collection of microorganisms that live within the gastrointestinal tract, provides crucial signals for the development and function of the immune system. Our gastrointestinal tracts are lined with a thin, sticky mucous that is embedded with millions of both beneficial and harmful bacteria that live, grow, and metabolize. They also influence the susceptibility to many immune-mediated diseases and disorders. These microorganisms also influence human physiology, including nutrient metabolism. There is also a connection between our gastrointestinal tract and brain and the immune system is an important regulator of these interactions. The gut microbiota also plays a role in maintaining intestinal barrier integrity and an intact intestinal barrier helps maintain gut health and overall good health of the body by preventing tissue injury, pathogen infection and disease development. The intestinal barrier takes part in intestinal immune responses through the secretion of cytokines, chemokines, antimicrobial peptides, and mucins. When the intestinal barrier function is compromised or when communication between the gut microbiota and the rest of the cells in the body go amiss, then dysbiosis (an unhealthy and unbalanced gut microbial environment) can occur. The gut needs to harbor beneficial microbes but keep pathogens at bay, and that is where the intestinal barrier plays a crucial role. When the integrity of the barrier is compromised, then hyper-permeability occurs, leading to an infiltration of microorganisms, toxins, and antigens. This is also known as “leaky gut”. Inflammation and infections are prone with leaky gut and can lead to further inflammation and infection in other systems of the body.
In the gut, the quantity and diversity of microbial species increase from the stomach to the colon, with the colon being the densest and most metabolically active community. In fact, the human intestine is considered as one of the most densely populated microbial ecosystems on Earth. There are many factors that can influence the composition of the gut microbiota, including diet, age, medications, illnesses, stress, and lifestyle.
Dietary Factors
Everything that we eat and drink passes through the gut along the gastrointestinal (GI) tract. Probiotics, prebiotics, polyphenols, other dietary components such as vitamins and minerals, and food-derived chemicals by microbiota (like short-chain fatty acids and bioactive peptides) are all beneficial for our gut microbiota. Probiotics and prebiotics can modulate gut microbiota to enhance the intestinal immune system and polyphenols have anti-inflammatory properties. Just as there are supportive foods for our gut health, there are also harmful foods that can disrupt the balance of the environment. Refined foods and fried foods are examples of these harmful foods, and different types of alcohol and caffeine can also be harmful to the bacteria.
Probiotics
Probiotics are live organisms. They are commonly found in different food sources but also as supplements. Probiotics have been shown to increase the good gut bacteria, maintain gut health and prevent chronic bowel disease and restore leaky gut. Probiotic-containing foods include:
Fermented dairy products (such as yogurt and kefir)
Siggi’s Icelandic Skyr – 4% milkfat; 2% Fage Total; Stoneyfield Farm Organic Plain Whole milk yogurt; Brown Cow plain whole milk yogurt; Chobani non-fat plain Greek yogurt; Wallaby Organic Greek plain whole milk yogurt
Sauerkraut (from the refrigerated section)
Kombucha (fermented black tea)
Kimchi (fermented cabbage)
Tempeh
Miso (fermented soybeans)
When choosing probiotic supplements, look for:
Shelf-stable
Supplements containing at least 15 billion CFUs (colony forming units); 100 billion is even better!
Supplements with multiple bacterial strains instead of only 1 or 2 (look for ones with 5 or more)
Supplements that state “live and active cultures” not “made with active cultures”
Probiotic supplements are not typically recommended if you have a compromised immune system, so make sure to check with your doctor before starting.
Prebiotics
Prebiotics are the fermentable fiber (nutrients/foods) that feed the good gut bacteria. Plants are going to be the biggest sources of prebiotics, and you can also find prebiotics added to probiotic supplements. Prebiotic foods include, but are not limited to:
Dried beans and other legumes
Garlic
Asparagus
Onions
Leeks
Jerusalem artichokes
Green bananas (they contain a resistant starch)
Whole wheat and wheat bran (do not consume if you have a sensitivity or allergy)
Chicory root
Dandelion greens
Apples
Barley
Oats
Cocoa (also a polyphenol)
Flaxseeds
Yacon root (similar to sweet potatoes)
Jicama root
Sprouted vegetables
Polyphenols
Polyphenols are plant chemicals that are digested by the gut bacteria and increase the healthy/good gut bacteria. Polyphenol-rich foods include:
Cloves, star anise and other seasonings (like dried peppermint, oregano, sage, rosemary and curry powder)
Cocoa powder and dark chocolate (look for 75% or higher dark chocolate)
Berries (blueberries, blackberries, strawberries, red raspberries)
Black currants, plums, sweet cherries, apples, red grapes
Beans (black beans and white beans have the highest amounts)
Nuts (hazelnuts, walnuts, almonds, pecans)
Artichokes, chicory root, red onions and spinach, broccoli and broccoli sprouts
Soy and soy-based foods
Black and green teas
Red wine (in moderation)
Black olives
Ginger
Whole grain flour such as wheat flour and rye flour
Potatoes
Flaxseeds
Extra virgin olive oil
Short-Chain Fatty Acids
Short-chain fatty acids, such as butyrate, propionate, and acetate as the most common, are byproducts made by the gut bacteria digesting fiber. Short-chain fatty acids have beneficial effects on immunity, inflammation and also our brain health. Feeding the gut bacteria with fibrous foods (previously mentioned) will create these chemical byproducts. However, there are foods that contain small amounts of butyrate. These include:
Ghee (clarified butter that is also considered gut-healing)
Butter
Milk
Cheese
Yogurt with live cultures
The biggest piece of nutritional advice to take away from this post is make sure to feed our gut bacteria with healthy and high-quality foods to help maintain a balanced microbial ecosystem and keep the intestinal barrier intact. In turn, this will give our immune system a fighting chance. Focus on plant foods at every meal and eat foods that are nutrient-dense, high in fiber and have a low glycemic load. Include the colors of the rainbow from various fruits and vegetables. Consume whole grains, probiotics, nuts and seeds, and incorporate a variety of seasonings (other than salt) to your dishes. A healthy and happy gut microbiome is going to make for a happier and healthier mind and body!
Sources:
Murphy L.Y. Wan, K.H. Ling, Hani El-Nezami & M.F. Wang (2018): Influence of functional food components on gut health, Critical Reviews in Food Science and Nutrition. doi:10.1080/10408398.2018.1433629.
Rooks MG, Garrett WS. Gut microbiota, metabolites and host immunity. Nat Rev Immunol. 2016; 16(6):341-352. doi:10.1038/nri.2016.42.
Spiljar M, Merkler D, Trajkovski M. The immune system bridges the gut microbiota with systemic energy homeostasis: focus on TLRs, mucosal barrier, and SCFAs. Front. Immunol. 2017. https://doi.org/10.3389/fimmu.2017.01353.
Zanteson L. Gut health and immunity – it’s all about the good bacteria that can help fight disease. Today’s Dietitian. 2012; 14(6):58. https:// www.todaysdietitian.com/newarchives/060112p58.shtml.
