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A Tale of Two COVIDs: Animal-Based vs Vegetarian “Terrain”

germ theory, covid, terrain theory, gut health, microbiome

By Kelley Herring

I recently received news from two friends, who became sick and tested positive for COVID, after spending a weekend together in the same house.

One friend wrote me a text that said, “I feel miserable. My whole body is sore. I can hardly get out of bed. I have never felt this sick.” Thankfully, she recovered after a week of severe (although not life threatening) flu-like symptoms and another week of rest.

My other friend sent an email, describing his symptoms: “I felt some lung irritation and low energy the first day. Mild headache and low-grade fever the next day. On the third day, I woke up rested and feeling about 95%. Back to normal soon after.”

Several other people were also in the house that weekend, who did not become sick at all.

Assuming they were all exposed to the same pathogen, is there something that could explain the severity of symptoms for one person… while another experienced a very mild case… and others didn’t become sick at all?

It turns out there is a very plausible explanation, backed by more than a century of hard science. We’ll get to that in a moment. But first, allow me to compare and contrast the two people who became ill:

  • My friend who was mildly ill and recovered quickly is young and in great physical condition. He gets sun every day on the beach in Southern California and eats a diet consisting almost entirely of meat.

  • My friend who became very ill is also young and in great physical condition. However, she lives in a cold, snowy climate, where her vitamin D status is compromised. And she consumes a vegetarian (bordering on vegan) diet.

Is it possible that these differences in their “diet and lifestyle” could explain why they were affected so differently by what would appear to be the same illness? And might it also explain why others were not affected at all – despite the same “exposure” to the virus?

Today, we delve into how the immune system works… why your individual “terrain” matters so much… and the potential effects of a plant-based vs. animal-based diet on your immune system.

First, let’s take a quick look at how we get sick…

gut fungus, emulsifiers, additives, One of the most important, yet forgotten, organs is your microflora. Microflora is vital to your overall health.

Your Immune System: Terrain Theory vs. Germ Theory

Whether you get sick (or not) has much less to do with the “bugs” you are exposed to… and far more to do with your internal “immune arsenal”. And what is within you is directly influenced by your diet and lifestyle (ie. sleep, stress, sunlight, exercise).

This is a very important distinction. And it highlights two diametrically-opposing theories of how microbial disease occurs…

The “Germ Theory” of disease was popularized by Louis Pasteur (1822-1895). It states that there are external germs, which invade the body and cause disease. Under this theory, regaining health depends on killing whatever germ made you sick and preventing microbes from entering your body in the first place.

Unfortunately, this theory is still largely used in “modern medicine”. And it is to credit for the global catastrophe of antibiotic resistance we now face. Not to mention, more recent mask mandates.

Germ theory was partly shaped around Pasteur’s fatally-flawed idea that the inside of the human body is sterile and devoid of germs. Of course, we now know this premise is incorrect. In fact, our bodies actually contain far more bacterial cells than human ones!

Pasteur failed to account for the microbiome – the vast collection of microbes that live in, on and around us – and its role in protecting health and preventing disease.1 We now know that our microbiome influences everything from our weight and metabolism, to our risk for cancer and neurodegenerative disease… and even our mood and mental health!2

Proponents of germ theory believe we must combat and avoid germs at all times to escape infection. To avoid getting ill, we must stay away from other humans, slather ourselves and the items we touch with “sanitizer” and wear a mask to extinguish microbial threats in the environment.

The opposing “Terrain Theory” of disease – conceptualized by Claude Bernard (1813-1878) and built upon by Antoine Bechamp (1816-1908) – postulates that it is not the “germ” that causes disease. Rather, it is the state of our internal health and our own innate ability to maintain homeostasis in the face of “unfriendly” organisms that keeps us well.

We now know that this theory is true thanks to the 86,671 (and counting!) studies published at PubMed on the microbiome and how it profoundly influences every aspect of human health.3 Terrain theory is bolstered by our growing understanding of the immune system and how it is positively (or negatively) affected by our diet and lifestyle choices.

If we follow the terrain theory, we know that staying healthy means optimizing the health of our microbiome and providing our immune system the nutrients it needs to function optimally. After all, the vast majority of our immune system – over 90%! – lies in our gut. And it is directly influenced by the foods we eat!4

When our gut bugs are in a healthy balance, they produce a myriad of immune-boosting substances that prevent microbial infections and ward off chronic illness. Through sound nutrition, and avoiding toxic inputs that harm our microbiome, we create a “hostile terrain” for viruses and other microbes.

It is the health of your own “terrain” that protects you… or puts you at risk for disease.

Building a healthy “terrain” means eating whole, nutrient-dense foods that contain the vitamins, minerals, amino acids and other substances that support immune function… while avoiding those foods and substances that can hamper it.

There is considerable evidence that an animal-based diet is the key to a strong, resilient and robust immune system… as well as evidence that a plants-only diet could leave you deficient in critical nutrients that negatively impact your “terrain” and therefore your immune health…

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Plants-Only Diet Shown to Reduce Immune Function

A recent study published in the journal Epidemiology analyzed a group of women, who were either vegetarians or omnivores.

The researchers evaluated the women’s blood, analyzing how efficiently their bodies made two types of “lymphocytes” (white blood cells) that are important to the immune system: T cells and B cells. They also looked at how effectively these immune cells could attack and engulf foreign invaders (a process called phagocytosis).

The researchers found significant differences in the immune function of vegetarians vs. omnivores:

  • All vegetarians in the group had lower white blood cell counts, compared to omnivores

  • All vegetarians showed lower levels of phagocytosis than omnivores, implying a weaker ability to neutralize pathogenic microbes

  • All vegetarians showed decreased “respiratory burst” of phagocytic cells compared to omnivores. This is the rapid increase in reactive oxygen required to kill microbes.5

  • The older vegetarians in the group exhibited significantly suppressed “proliferative response” of T-lymphocytes. This refers to the ability to rapidly produce T cells in quantities sufficient to squelch a microbial threat.6

It is easy to see how a reduced ability to produce white blood cells, coupled with an inability for those cells to extinguish a pathogen, could result in more frequent and more serious illnesses.

But what is it about an omnivorous diet that strengthens the immune system?

The key lies in a symphony of powerful immune-building nutrients that form the foundation of the cells of your immune system that are designed to protect you.7

To stay healthy and minimize our risk of getting sick, we don’t have to hide under a rock or stop living our lives. We simply need to support our immune system with a nutrient-dense diet. The good news is that when you rely on the true “superfoods” enjoyed by our ancestors, staying healthy comes naturally.

And please stay tuned for my next article, where I will reveal the most powerful immune-boosting nutrients (found primarily in an animal-based diet) that you need to stay healthy and build a bulletproof immune system.

Read more health and wellness articles from Kelley Herring on our Discover Blog.

kelley herring


Kelley Herring is the author of the brand new book Keto Breads – which includes more information you need to know about why it is so important to avoid wheat and grains in your diet, plus how to use healthy replacements for these foods to create all the breads you love… without the gluten, carbs and health-harming effects. Click here to learn more about Keto Breads


1. W.C. Summers,History of Microbiology,Editor(s): Thomas M. Schmidt, Encyclopedia of Microbiology (Fourth Edition), Academic Press, 2009, Pages 593-607, ISBN 9780128117378,

2. Barko PC, McMichael MA, Swanson KS, Williams DA. The Gastrointestinal Microbiome: A Review. J Vet Intern Med. 2018;32(1):9-25. doi:10.1111/jvim.14875

4. Erika C Claud, W. Allan Walker, Chapter 5 – The Intestinal Microbiota and the Microbiome, Editor(s): Richard A Polin, Josef Neu, Gastroenterology and Nutrition: Neonatology Questions and Controversies, W.B. Saunders, 2008, Pages 73-92, ISBN 9781416031604,

5. Berton, Giorgio & Dusi, Stefano & Bellavite, Paolo. (1988). The Respiratory Burst of Phagocytes. 10.1007/978-1-4684-5496-3_2.

6. Neubauerova, E; Tulinska, J; Kuricova, M; Liskova, A; Volkovova, K; Kudlackova, Met al The Effect of Vegetarian Diet on Immune Response, Epidemiology: September 2007 – Volume 18 – Issue 5 – p S196 doi: 10.1097/01.ede.0000289012.66211.45

7. Gombart AF, Pierre A, Maggini S. A Review of Micronutrients and the Immune System-Working in Harmony to Reduce the Risk of Infection. Nutrients. 2020 Jan 16;12(1):236. doi: 10.3390/nu12010236. PMID: 31963293; PMCID: PMC7019735.