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 like heavily processed foods, sugar and soda is also a key to enrich the microbiome and boost immunity.
In this article, we’ll delve deep into 6 types of foods that boost the immune system (and an additional 30 foods that are high in immune-boosting compounds).
1. Yellow Bell Peppers
Contrary to popular belief, oranges are not particularly high in vitamin C when compared to other fruits. 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, which is ok. The reason that yellow bell peppers are top of our list is they are easy to get in most parts of the world and contain 152%DV of vitamin C. Yellow bell peppers contain more vitamin C as they mature (up to a point). Green bell peppers have half the amount of vitamin C, about the same amount as an orange.
Vitamin C boosts the immune system by influencing the development and functioning of lymphocytes. About half a cup of yellow bell peppers will provide 152% DV o 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 winter – 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. Lycopene is a powerful antioxidant and 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.
Other foods that are rich in lycopene include: Tomatoes (sun-dried, pureed, fresh and canned), watermelon and red/ pink grapefruit.
Broccoli is high in phytonutrients like vitamin A, C and E. Ensuring high-quality intake of essential nutrients boosts the immune system. Broccoli is also rich in sulforaphane. Sulforaphane 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.
Other foods that contain sulforaphane include: Kale, cabbage, Brussels sprouts, bok choy, watercress and cauliflower
Turmeric is a great immune-boosting food due to its support of healthy inflammatory pathways. Inflammation is implicated in the pathophysiology of many health-compromising situations, so consuming pro-healthy-inflammation foods 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.
Turmeric is the only food that contains curcumin.
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 big the reasons that plants are good for you as flavonoids boost the immune system.
Other flavonoid rich foods include: Cranberries, apples, blueberries, broccoli, and strawberries
Almonds are rich in fat-soluble vitamin E. Vitamin E boosts the immune system as it’s a free radical scavenging antioxidant. Almonds are easy to find and store in any season, making them a great winter pantry staple.
Consume almonds with their skin on as a lot of their 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 improved the white blood cells’ ability to detect viruses.
Other vitamin E rich foods include: Wheat germ oil, sunflower seeds, hazelnuts and peanuts.
Eating a varied diet that is bursting with plant-based nutrition is the 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.