Foods, Digestion and Immunity - What's the Connection?

By Sarah Holvik, B.Sc. Nutritional Sciences

Considering our knowledge of the intimate relationship between our digestive and immune systems, we should never get sick. Armed with information, we could manipulate our diets in such a way that conditions such as inflammatory bowel disease, hypertension, lowered immunity and cancer would not exist. However, the truth is that the modern Western diet does not tip the scales in our favor in terms of immunity. In fact, research now shows that the average Western diet can actually weaken our immune systems and make us more prone to disease. However, there is hope. Let’s discuss some foods with potent immune-boosting effects due to their influence on our digestive systems.

Intestinal Immunity - How it works

To discuss how foods can impact overall immunity through their effect on the gastrointestinal (GI) tract, we need to first explore the role of the GI tract in regulating immunity. The GI tract has both direct and indirect effects on immune function and the resulting ability to ward off disease. Directly, the lining of the intestine is protected by a local immune system called gut-associated lymphoid tissue (GALT). Because GALT is the largest lymph system in the human body, the digestive tract has the most profound effect on overall immunity among all the internal organs. Indirectly, the GI tract contains hundreds of bacterial species in the large intestine that are both beneficial and harmful to the body. The balance of these bacteria in the gut is also a very important factor in the intestine’s defense system against disease.

When this balance is disrupted, harmful bacteria such as E. coli can take over the intestine, causing infection. Stress, inflammation and certain foods can also disrupt both the GALT system and intestinal microflora balance, making us more susceptible to disease.

So, what foods positively influence our intestinal environment to promote optimal immunity?

Probiotics & Prebiotics

One way to promote intestinal immunity is by consuming probiotics and prebiotics. Probiotics are live bacteria food supplements that benefit the body by improving its intestinal microflora balance. Prebiotics are nondigestible fibers that selectively stimulate the growth of specific probiotic bacteria in the colon. By introducing these food supplements into our diets, we can support our body’s natural defense barrier against disease and promote optimal health.

Probiotics have both immune (ie. influence GALT tissue) and non-immune (ie. influence microflora balance) mechanisms for increasing our defense against disease. The majority of probiotics can be classified into two distinct bacterial classes — Lactobacillus and Bifidobacteria. These two species act in similar but distinct ways, and can be used to address a variety of specific health concerns. Lactobacillus species help with lactose digestion, relieve infant diarrhea, increase our resistance to infections and help relieve the symptoms of irritable bowel syndrome such as constipation and diarrhea. On the other hand, Bifidobacteria species stimulate the immune system, prevent the growth of harmful bacteria, produce B vitamins and help to restore microflora balance after antibiotic treatments. It is important to note that because probiotics are live bacteria, they must be kept refrigerated in order to remain effective.

Simply put, prebiotics are specific fibers that act as food for probiotic bacteria in the intestine, enhancing their stimulatory effect on the immune system. Prebiotic fibers are naturally found in foods such as whole grains, onions, bananas, garlic, honey, leeks and artichokes. However, the level of prebiotics in foods alone does not significantly enhance the growth of probiotic bacteria, so to fully benefit from prebiotics we must consume them in either fortified foods or supplements. Specific prebiotic fibers include inulin, fructo-oligosaccharides (FOS), polydextrose, lactulose and lactitol.

Eat Your Fruits and Vegetables!

All raw fruits and vegetables contain enzymes and fiber that enhance our intestinal health and by extension, our immunity. However, many fruits and vegetables that have specific effects on our digestive and immune function can easily be added to our diets. For example, garlic stimulates GALT tissue in the intestine and allows for elimination of waste products from the body. Spirulina and chlorella are potent green foods rich in chlorophyll, minerals and antioxidants that promote cell growth and immunity. Ginger supports healthy digestion and immunity by enhancing white blood cell production. Parsley is one of the best foods and acts like a multivitamin due to its extremely high nutrient content; it is made up of 20% protein, antioxidant flavonoids, iron, calcium, phosphorus, manganese, inositol, sulfur, vitamin K, beta carotene, and vitamin C. Parsley helps eliminate harmful microbes from the body due to its anti-bacterial and anti-fungal effects, and as such may be used to enhance our natural defense against disease. Keep in mind that the digestive and immune-enhancing foods discussed here are just the tip of the iceberg; fruits and vegetables are some of the best natural immune-boosting substances in the world.

Undoubtably, the connection between digestion and immunity is very intricate and complex. The best way to optimize your defense against disease is to customize your diet to include foods that naturally support the body’s optimal function.