The immune system provides a robust anatomical barrier that serves as a host defense mechanism. One of these anatomical barriers is the gastrointestinal tract, inside which there are many defense mechanisms such as peristalsis, gastric acid, bile acids, digestive enzymes, flushing, thiocyanate, defensins and gut flora. The gut flora (microbiota) is a key focus for many immunologists; however, all of these essential defense mechanisms rely heavily on the entire gastrointestinal tract functioning efficiently.
Planning meals that benefit the immune system is a great way of fighting off infection. Pre- and probiotic-rich foods enhance microbial diversity in the gut, while vitamin C-rich foods mop up free radicals. Additionally, avoiding foods that promote infection, such as heavily processed and sugar-laden foods, is also a key to enrich the microbiome and boost immunity.
In this article, we’ll take a close look at some of the foods that boost the immune system.
1. Yellow Bell Peppers
Contrary to popular belief, oranges are not particularly high in vitamin C when compared to other fruits. For example, the Kakadu plum contains 100 times more vitamin C with 530% DV; however, unless you live in Australia, Kakadu plums might be a bit hard to source.
One orange provides 78% DV of vitamin C. Yellow bell peppers are top of our list because they are easy to find in most parts of the world and contain 152% DV of vitamin C. Green bell peppers have half the amount of vitamin C, about the same amount as an orange.
Vitamin C supports the immune system by influencing the development and functioning of lymphocytes. About half a cup of yellow bell peppers will provide 152% DV of vitamin C.
If you live in Mexico or South America, you can easily find fresh guava. For everyone else, guava juice is another option. What’s more, guava season is mainly during the winter months - November through April, which is perfect timing for an immune system boost. Guava contains 140% DV of vitamin C and is also rich in lycopene, a powerful antioxidant that plays an important role in the enzyme activities in the immune system.
One randomized controlled study found that eating 400g of guava per day lowered blood pressure as well as serum total cholesterol, triglycerides and LDLc. Interestingly, guava without the peel was found to be more effective.
Additional Foods rich in lycopene include: tomatoes (sun-dried, pureed, fresh and canned), watermelon and red/pink grapefruit.
Broccoli contains high levels of phytonutrients such as vitamins A, C and E. Broccoli is also rich in sulforaphane, a compound that is activated when the vegetable is chewed, cut or damaged. It’s important to note that raw broccoli or broccoli sprouts contain the highest levels of sulforaphane. Minimizing boiling or cooking and eating sulforaphane-rich foods as raw as possible will provide maximum health benefits.
Sulforaphane has been found to support healthy inflammation pathways and blood pressure in animal models. Sulforaphane has a wide range of health benefits that include cognitive protection and blood stabilization. In one study, fasting blood sugar was significantly reduced (by 6.5%) in participants that consumed sulforaphane.
Additional foods that contain sulforaphane include: kale, cabbage, Brussels sprouts, bok choy, watercress and cauliflower.
Turmeric is an important immune-boosting food due to its support of healthy inflammatory pathways. Inflammation is implicated in the pathophysiology of many health-compromising situations, so consuming foods that support these pathways is an ideal way to boost the immune system.
Turmeric has a host of other beneficial health-promoting mechanisms, including its anti-oxidative, anti-cytotoxic, neurorestorative properties, as well as having metal-chelating properties, making it an important staple in an immune-boosting pantry. Curcumin is the active component in turmeric that offers all of the health benefits of this ancient golden root.
5. Green Tea
Green tea contains L-theanine, which promotes relaxation and the formation of healthy T-cells. Black tea also contains L-theanine (sometimes in higher doses). However, black tea is often fermented, reducing the L-theanine properties.
Green tea is packed with flavonoids and epigallocatechin gallate (EGCG). Flavonoids are one of the big reasons that plants are good for you as flavonoids boost the immune system.
Additional flavonoid-rich foods include: cranberries, apples, blueberries, broccoli, and strawberries.
Almonds are rich in fat-soluble vitamin E, a powerful free radical scavenging antioxidant, thus, an important nutrient for immune system health. Almonds are easy to find and store in any season, making them a great winter pantry staple.
A good amount of almonds’ health-promoting properties are contained in the skin. In one study from the Institute of Food Research in Norwich and the Policlinico Universitario in Messina, Italy, researchers found that almonds may improve white blood cells’ ability to detect viruses.
Additional vitamin E rich foods include: wheat germ oil, sunflower seeds, hazelnuts and peanuts.
Consuming a varied diet that is bursting with plant-based nutrition is a vital key to boosting the immune system. Other foods that add to the immune-boosting arsenal include prebiotic foods like garlic, leeks and onions, and also probiotic foods like miso, pickles, sauerkraut and tempeh.
As cold and flu season approaches, be sure to stock your fridge with those foods that will fight for your health.