• Allison Fahrenbach

Is Processed Food Wrecking Your Immune System?

If what you eat can make you well, then can what you eat also make you sick?


What you eat can determine whether or not you get sick by way of how your food choices strengthen or suppress the health of your immune system.

What Is The Immune System?

On a daily basis, we are all constantly exposed to potentially harmful microbes. Our immune system is our defense. It is a network of intricate stages and pathways in the body that works to guard against harmful foreign invaders like bacteria, viruses, and parasites.

Humans have two types of immunity: innate immunity and adaptive immunity.

Innate immunity is a first-line defense from pathogens that try to enter our bodies, achieved through protective barriers.

These barriers include:

  • Skin that keeps out the majority of pathogens

  • Mucus that traps pathogens

  • Stomach acid that destroys pathogens

  • Enzymes in our sweat and tears that help create anti-bacterial compounds

  • Immune system cells that attack all foreign cells entering the body

Adaptive or acquired immunity is a system that learns to recognize a pathogen. It is regulated by cells and organs in our body like the spleen, thymus, bone marrow, and lymph nodes.

When a foreign substance enters the body, these cells and organs create antibodies, which are blood proteins produced in response to and to counteract antigens.

Our immune system then adapts by “remembering” the foreign substance/antigen so that if it ever enters again, your antibodies efficiently and quickly act to destroy it.

While there are many foods you can eat to support the health and function of your immune system, food is also, unfortunately, one of the largest contributory factors to poor immune health.

Diets that are limited in variety and lower in nutrients, consisting primarily of processed foods have been shown to negatively affect a healthy immune system.


By promoting disturbances in healthy intestinal microorganisms, resulting in chronic inflammation of the gut, and associated suppressed immunity. Over 70% of your body’s immune system is located in your gut so logically speaking, the health of your microbiome is crucial to the health of your immune system.

The microbiome is an internal metropolis (so to speak) of trillions of microorganisms or microbes that live in our bodies, mostly in the intestines.

It is an area of intense and active research, as scientists are finding that the microbiome plays a key role in everything from our mood to our mental health, our bodyweight and our immune function.

The gut is a major site of immune activity and the production of antimicrobial proteins and diet plays a large role in determining what kinds of microbes live in our intestines.

For example a high-fiber plant-rich diet with plenty of fruits, vegetables, whole grains, and legumes has been shown to support the growth and maintenance of beneficial microbes while a diet high in sugar and processed foods not only deprives good microbes of the food they need to thrive but also contributes to the overpopulation of bad microbes.

A diet high in processed food does this in two ways:

1-Processed foods are low in nutrients and epidemiological studies have found that those who are poorly nourished are at greater risk of bacterial, viral, and other infections. Additionally, animal studies have found that deficiencies in zinc, selenium, iron, copper, folic acid, and vitamins A, B6, C, D, and E can alter the response of the immune system.

Fast food in particular has even been linked to immune system aggression, meaning it causes a complete misfiring or an overreactory response of the immune system. This is what’s known as inflammation. As you continue to bombard the body with more and more salt, sugar and fat, the immune cells further overreact and inflammation starts to run rampant. This chronic inflammation impairs the immune system's ability to respond when you come into contact with an antigen.

One study published in Nutrition Journal looked at the impact of fast food consumption and lifestyle choices on people’s immune function. It found that the large number of calories in processed and fast food contributed to health problems such as increased inflammation, reduced control of infection, increased rates of cancer, and increased risk for allergic and auto-inflammatory disease.

What’s more these food and lifestyle choices can permanently change the balance of bacteria in the body. And since microbes are passed from mother to child during vaginal births it also means those damaging changes can be passed to your kids.

2-Processed foods feed bad microbes, causing the wrong bacteria and yeast to grow. Increases in these pathogenic bacteria often leads to a condition known as dysbiosis which is a fancy term for a microbial imbalance or maladaptation inside the body such as an impaired microbiome.

The overgrowth of pathogenic bacteria also crowds out beneficial bacteria, causing changes in the internal mucosal barrier of the intestine. With fewer beneficial bacteria standing guard along this barrier, its permeability is altered, which means that unwanted substances can slip through, like holes in a wall.

This then creates what is popularly known as "leaky gut syndrome" where the body launches an inflammatory immune response targeting these substances that have snuck through the holes in the intestinal wall. This inflammation not only generates symptoms like constipation, gas and bloating, joint pain, lethargy, headaches, memory loss, skin rashes, or eczema- it also increases your susceptibility to infection and sickness.

The consumption of processed, simple sugars can even reduce white blood cell phagocytosis. Phagocytes are a type of white blood cell that use phagocytosis to engulf bacteria, foreign particles, and dying cells in order to protect the body.

And saturated fats, which are noted to be proinflammatory, may enhance the prostaglandin system and alter immune cell membranes, disrupting their function.

The takeaway in all this?

The choices you make about the food you eat plays a critical role in supporting the immune system. Your immune system is on duty 24 hours a day, 7 days a week, 365 days a year, over 70% of which is in your gut- where trillions of immune-modulating bacteria reside. You want to make sure you eat to keep this environment strong and healthy.

It can be overwhelming to think about all of the bacteria, viruses, fungi and other potentially disease-causing microorganisms we come into contact with on a daily basis but as long as your immune system is functioning well, you will largely be able to resist infection.


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  2. Guillin OM, Vindry C, Ohlmann T, Chavatte L. Selenium, selenoproteins and viral infection. Nutrients. 2019 Sep;11(9):2101.

  3. Wessels I, Maywald M, Rink L. Zinc as a gatekeeper of immune function. Nutrients. 2017 Dec;9(12):1286.

  4. Molendijk I, van der Marel S, Maljaars PW. Towards a Food Pharmacy: Immunologic Modulation through Diet. Nutrients. 2019 Jun;11(6):1239.

  5. Caballero S, Pamer EG. Microbiota-mediated inflammation and antimicrobial defense in the intestine. Annual review of immunology. 2015 Mar 21;33:227-56.

  6. Li XV, Leonardi I, Iliev ID. Gut mycobiota in immunity and inflammatory disease. Immunity. 2019 Jun 18;50(6):1365-79.

  7. Chandra RK. Nutrition and the immune system: an introduction. The American journal of clinical nutrition. 1997 Aug 1;66(2):460S-3S.

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