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How Diet Can Impact Your Immune System

The Cabinet — 08.17.20

Nutrition foundationally helps our bodies function at the most optimal level. We sat down with Dr. Paul Grewal, author of the NY Times bestselling book, Genius Foods, and a scientific advisor to Hilma, to help us digest the connection between diet and our immune system.

The Background

The immune system is built to fight off pathogenic, foreign invaders that are entering the body. In order for it to best do its job, our immune system needs proper nourishment and support so that it can identify when it needs to mobilize for protection. However, when we eat things that disrupt the immune system’s daily functions, it can either become overactive, which leads to inflammation, or underactive, which leaves us vulnerable to illness and infection. Dr. Grewal cautions that only 12% of Americans are thought to be “metabolically healthy” by metrics of insulin resistance, sugar tolerance, blood pressure, weight, and other measures.
The health quality of immune cells and proteins is determined by a natural balance of nutrients. The body’s immune response relies on micronutrients, which are the vitamins and minerals that come from our food. 

Food As Medicine

Supporting the immune system with a healthy diet goes much deeper than the food itself. Strengthening your immune system and developing resilience to chronic illness and inflammation starts in the gut, meaning the food we eat should support our microbiomes (the place with all the really good bacteria).

Our microbiomes are made up of trillions of microorganisms that send messages to our brains, control immune activity, and manage our bodies’ hormone production. Therefore, our diets become the key determinants in the quality and diversity of microbes living in our intestines.

A nourishing diet starts with eating foods that are rich in vitamins, minerals, and nutrients. Dr. Grewal explains that the same foods we consider ‘healthy’ — sufficient protein, healthy fats, colorful veggies, starches and fruit (to match your activity level) — will generally be good for your immune system. Specifically, foods like fiber-rich plants, fruits, vegetables, and legumes are densely-packed with vitamins and minerals like vitamins C and D, zinc, selenium, and iron. Each of which is essential to storing up resilience and immune health.

Processed foods, on the other hand, tend to trigger immune responses. These high-refined carbohydrate, fiber-less foods lack essential nutrients and quickly turn into sugar. This can cause the body to attack itself, leading to pain, inflammation, and exacerbated chronic illness. It can also debilitate immune cells’ ability to act quickly, compromising their healing and protective powers.  

The Superstars

Vitamin C

Vitamin C is an all-star for supporting your immune health. Dr. Grewal noted that blood levels of Vitamin C have been shown to drop during certain viral infections. Vitamin C also supports and expedites healing, thanks to its production of collagen and L-carnitine. It can be found in citrus foods, dark leafy greens, sweet potatoes, tomatoes, and strawberries. Not only does it contain elements like carbon and oxygen, but it also does not store up in the body. This means your body is able to get rid of whatever Vitamin C it doesn’t need.


“Zinc is essential to the pathogen-killing capacity of immune cells,” Dr. Grewal explains. Innate immune cells need it to develop and function properly, therefore allowing them to defend your body against infections. Dr. Grewal suggests that zinc deficiency is very common, so “sensible supplementation at the onset of symptoms or at the time of harmful exposure is not unreasonable.” Zinc deficiencies, over time, can lead to poor wound healing, alopecia, rough skin, and a foggy brain. Legumes, nuts, red meat, shellfish, eggs, and whole grains are excellent food sources for zinc.


Vitamins C and E, selenium, and carotenoids (yes, they are found in carrots) are high-powered antioxidants that may prevent or delay cellular damage. How? Dr. Grewal explains that “in a healthy state, the body actually makes its own very powerful antioxidants.” However, the antioxidant capacity of the body can be overwhelmed by dietary, environmental, and psychological stress. These stressors are known as free radicals, which can lead to oxidative stress when out of balance with antioxidants in the body. Not only does oxidative stress lead to premature aging, but it can also contribute to long-term chronic illness and disease. “Dietary antioxidants, like those found in colorful fruits and veggies, can neutralize damaging free radicals in the intestine under certain conditions,” says Dr. Grewal.


1. “Nutrition and Immunity.” The Nutrition Source, Harvard School of Public Health, 23 July 2020, www.hsph.harvard.edu/nutritionsource/nutrition-and-immunity/.

2. Nordqvist, Joseph, and Debra Rose Wilson. “Vitamin C: Why We Need It, Sources, and How Much Is Too Much.” Medical News Today, MediLexicon International, 10 Apr. 2017, www.medicalnewstoday.com/articles/219352.

3. Prasad, Ananda S. “Zinc in Human Health: Effect of Zinc on Immune Cells.” Molecular Medicine (Cambridge, Mass.), ScholarOne, 3 Apr. 2008, www.ncbi.nlm.nih.gov/pmc/articles/PMC2277319.

 4. “Antioxidants: In Depth.” National Center for Complementary and Integrative Health, U.S. Department of Health and Human Services, Nov. 2013, www.nccih.nih.gov/health/antioxidants-in-depth.

This information is for educational purposes only and should not be taken as medical advice. Please consult a physician before treating any disorder.

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