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Research shows that the gut plays an even more complex and pivotal role in our overall health than we previously assumed. Beyond digestion, the gut has an impact on the functioning of our body, mind, and immune system. The immune system is defined as the network of cells, tissues and organs that work together to protect the body, helping to fight off sickness.1 When you do get an infection or become sick, a healthy immune system helps you fight infections and heal wounds – which of course is what we all want! Did you know having a healthy gut plays an important role in having a strong immune system? This is because the immune system relies on microbes in the gut to stay in proper working order.2
Let’s dive into how your gut and immune system are connected, and how nutrition plays a role!
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Whatever enters your gut isn’t truly ‘inside’ your body. All along the walls of your intestines, a single layer of cells forms the boundary between what’s in your gut and what gets absorbed and circulated to the rest of the body. These cells, together with the mucosal layer, gut microbiota, and immune system, make up the gut barrier.
A healthy gut barrier is selective about which substances are allowed to pass through. This is what we mean when we say your gut is like a gatekeeper. It offers 3 levels of defense against disease-causing microbes that try to gain access:
The gut microbiota is the population of bacteria, viruses, and fungi living all along the length of the intestines. The gut microbiota helps maintain the barrier. It crowds out potentially harmful bacteria by competing for space and food. The gut microbiota produces bacteriocins, which are antimicrobial molecules that are able to kill harmful bacteria. They also provide fuel (as short-chain fatty acids) to intestinal cells and shape immune responses.3
A healthy gut barrier is covered with a layer of mucus. These mucosal cells provide a physical and biochemical barrier that prevents harmful microorganisms and toxic substances from entering, while allowing beneficial nutrients to pass through. Scientists have found a lack of fibre in the diet erodes the mucous barrier, making you more susceptible to disease-causing bacteria.4
About 70% of the body’s immune system is located in the gut.5 Within the intestinal wall are special regions called gut-associated lymphoid tissue, or GALT.6 The GALT produces and stores immune cells that help with immune surveillance of what passes through the intestines. They recognize, identify, and neutralize any harmful substances that have found their way into the body.
Immune cells in the gut interact with the gut microbiota and are directly influenced by an individual’s diet and lifestyle. Those gut microbes are healthiest and support strong immunity when their hosts (that’s us) consume a healthy, balanced and diverse diet. Let’s get into the details.
Good nutrition is important for proper gut microbiota and immune function. A healthy, balanced diet and lifestyle can support our immune system, whereas a poor diet can compromise the immune system, leading to greater susceptibility to infections.7,8 Having a diverse diet consisting of a variety of foods will provide your body with the nutrients it needs for a healthy immune system.
Dietitians of Canada recommends getting your nutrients from food rather than supplements. This is because food provides protein, healthy fats, antioxidants and many vitamins and minerals that are essential for the proper functioning of the immune system.
Following a healthy eating pattern such as the one from Canada’s Food Guide will help get the nutrients you need. To be of more help, we have outlined the specific nutrients you need below with foods sources to get them from:9,10,11,12
|Nutrient||Function and food sources|
|Vitamin A||Contributes to the normal function of the immune system by aiding in the normal development of white blood cells which are critical to immune response and regulation. Food sources that are high in vitamin A include fruits and vegetables that are bright and colourful such as kale, spinach, and broccoli, red bell pepper, tomatoes, cantaloupe, and mango. For more sources of vitamin A, visit Unlock Food.|
|Vitamin B6 (pyridoxine)||Essential in the normal functioning of the immune system and is required as a coenzyme in the metabolism of antibodies and cytokines (molecules produced by immune cells). Good food sources include potatoes, beans, meat, chicken, and fish.|
|Vitamin B9 (folic acid/folate)||Plays an important role in the function of the immune system for the formation and increase of T lymphocytes (needed to protect the body from pathogens). Folic acid is the form found in vitamin supplements while folate is the form found in food. Folate can be found in: |
cooked dried beans, peas and lentils, spinach, asparagus, romaine lettuce, beets, broccoli, enriched grain products like pasta, cereals, bread, fruits such as cantaloupe, honeydew, grapefruit juice, banana, raspberries, grapefruit, and strawberries.
|Vitamin B12||Affects the immune system through its role in DNA and protein synthesis and is required for the formation of new immune cells or antibodies. The best food sources for Vitamin B12 come from foods like lean meats, poultry, fish, dairy products, and eggs. Learn more about vitamin B12 food sources here.|
|Vitamin C||Contributes to the normal function of the immune system and immune response through its antioxidative properties. Vitamin C is found in many fruits and vegetables. Try having a glass of orange juice or grapefruit at breakfast, raw peppers or cooked broccoli for an afternoon snack or ½ cup of strawberries for dessert! For more sources of vitamin C, click here.|
|Vitamin D||Essential to the function of the immune system and plays an important role in the regulation of inflammatory responses and antibody production. Vitamin D is not found in many foods, but some include: cow’s milk, margarine. fortified orange juice, fatty fish like salmon and sardines, and egg yolks. For more information on vitamin D, visit unlock food.|
|Zinc||Contributes to the normal function of the immune system and is important for the synthesis and function of immune cells. Zinc comes from a variety of different foods which include high protein foods such as: oysters, beef, pork, cheese (cheddar, swiss, gouda, brie, mozzarella) turkey, baked beans, and canned lentils. For more information on zinc, click here.|
|Iron||Is important for our immune function and required for the normal functioning of T lymphocytes (needed to protect the body from pathogens) and the production of cytokines (molecules produced by immune cells). Iron is found in a variety of animal foods, plant foods, and iron fortified products (like breads, pastas, and cereals). Some specific foods include: beef, pork, poultry, lamb, liver, kidney, oysters, shrimp, octopus, chicken, duck, quail, mackerel, trout, bass, tuna fish.|
|Copper||Is important for the energy production of immune cells and their protection against oxidative damage. Food sources of copper include: shellfish, seeds and nuts, oysters, baking chocolate (unsweetened) beef, and liver.|
|Selenium||Plays a key role in the immune system and is linked to the increase of T cells (needed to protect the body from infections). It can be found in foods such as oysters, liver, canned tuna, roasted pork, eggs, brazil nuts, and more.|
It is important to note that more isn’t necessarily better. There is no evidence that more of a nutrient, beyond our needs, will lead to a stronger immune system.
In fact, you don’t necessarily want your immune function to be above normal, because the gut microbiota works hard to maintain its homeostasis or balance.
If you are concerned about your nutrient intake or think you may need a supplement, speak to a registered dietitian. It’s best to check with your healthcare provider before taking any supplements. Both zinc and selenium can be toxic in high doses, and taking more than 2,000 mg of vitamin C per day can have side effects like diarrhea.13
The idea is to eat a variety of foods and a have healthy, balanced diet and lifestyle. In addition to providing a wide array of nutrients, the more diverse the diet, the more diverse the microbiota. Results from the American Gut Project indicate that having a greater number of plant types in the diet is associated with greater diversity of the gut microbiota,14 and gut microbial diversity is an important indicator of gut health and overall health.15 In a follow-up study, researchers also concluded that it is important to look at the diet as a whole, rather than individual foods, when it comes to the gut microbiota.16 In particular, the flexitarian dietary pattern was associated with greater microbial diversity.16 The Mediterranean diet, which is a type of flexitarian diet, is also linked to microbiota diversity.17
In summary, a rich diverse diet with a variety of foods, including certain fermented foods, probiotics and prebiotics, are important in helping us meet our nutrient needs and support the proper function of the immune system and gut microbiota.