The consumption of animal protein has been linked to various health problems, including a wide range of autoimmune diseases. While there is no general consensus in modern science about the exact connection, many well-known plant-based physicians are exploring how autoimmune diseases like type 1 diabetes, Hashimoto’s, lupus, rheumatoid arthritis, psoriasis, Crohn’s disease and even multiple sclerosis might be directly linked to animal protein intake.
Dr. John McDougall’s theory on autoimmune disease
In this article, we will focus in particular on the theory and treatment approaches of Dr. John McDougall (born May 18, 1947, died June 22, 2024). Dr. McDougall was very outspoken on this topic and reported many success stories of how he cured or significantly alleviated the symptoms of patients suffering from various autoimmune diseases by dramatically changing their diet.
Even though his theory, observations, experiments and personal experience have not been replicated by large-scale peer-reviewed studies, many of his colleagues share the general view that autoimmune diseases are indeed diet-related diseases. Some might call Dr. McDougall’s theory the most radical approach, but the logic behind it is worth examining.
When the body attacks its own cells and tissues
Autoimmune diseases are estimated to affect between 5% and 10% of the global population, corresponding to hundreds of millions of people worldwide. An autoimmune disease is defined as a condition in which the immune system mistakenly attacks the body’s own cells and tissues instead of protecting them.
This can affect any part of the human body, both internally and externally, and is generally considered irreversible but manageable by slowing down the progression of the disease or reducing the frequency of acute flare-ups.
There currently are more than 80 known autoimmune diseases, and some experts believe the number could be over 100 depending on how they are classified. The most common autoimmune diseases include:
- Hashimoto’s thyroiditis
- Rheumatoid arthritis
- Psoriasis
- Type 1 diabetes
- Inflammatory bowel diseases (e.g. Crohn’s disease)
Dr. John McDougall further lists Addison’s disease, alopecia (hair loss), ankylosing spondylitis, dermatomyositis, inflammatory arthritis, lupus, multiple sclerosis, myasthenia gravis, pernicious anemia, polymyositis, relapsing polychondritis, schizophrenia, scleroderma, ulcerative colitis, uveitis and vitiligo.
Leaky Gut: How Proteins Enter the Bloodstream
According to Dr. McDougall, any autoimmune disease begins in the intestinal tract. By eating the “wrong” types of food, we damage the gut lining and make it leaky. This does not happen overnight but develops over time through repeated injury from the daily diet. Dr. McDougall sees two main culprits at work: gluten toxicity and dysbiosis.
Regarding gluten, he explains it to be a rather hard-to-digest plant protein for the human intestine that can irritate the gut lining, cause inflammation and lead to lasting damage. Some people react more strongly to gluten than others, and such a strong reaction is known as celiac disease, which requires complete avoidance of gluten.
The second part of the equation is dysbiosis, which simply means that the gut is hosting the wrong types of bacteria that make up the microbiome. Our microbiome is a direct consequence of what we eat, and by changing our diet, our gut bacteria can in fact change incredibly fast.
Eating animal products sets us up for a problematic microbiome, which not only slows down digestion and inhibits the absorption of vitamins but also causes constant irritation and inflammation. In particular, the sulfur-containing amino acids found in high amounts in beef, chicken, tuna, eggs and certain cheeses are said to contribute to strong dysbiosis.
With a weak and damaged gut lining, we then open the door for substances to leave the intestines the wrong way and enter the body. This point is important to understand because the entire intestinal tract, from the mouth through the esophagus, the stomach, the small and large intestine, all the way down to the colon, is not considered to be “inside” the body.
It is a tunnel passing through the body, selectively allowing nutrients and water to be absorbed through the intestinal wall into the bloodstream, where they are then carried to the organs that need them. With a leaky gut, larger substances than vitamins, minerals or water can pass through the gut lining.
This can also include certain proteins, especially animal proteins, that the body was unable to fully break down. When these intact proteins pass through as well, the next important step toward an autoimmune disease is taken.
The immune system attacks the foreign protein
After passing through the intestinal wall, animal protein ends up in the surrounding tissue and from there quickly enters the bloodstream, where it is recognised as a foreign invader. The immune system responds by activating lymphocytes, which begin to identify and target these proteins.
As a result, antibodies are produced, marking these proteins for destruction and triggering an inflammatory response. So far, so good, one might think, but according to Dr. McDougall, this is exactly where a symptomatic autoimmune disease can begin. Animal proteins happen to be structured very similarly to our own human proteins.
People who defend a carnivorous diet often refer to this as an advantage, but it may in fact be the exact opposite. When the immune system has created antibodies against something that is so similar to components of our own tissues, it can no longer distinguish between what is foreign and what is self.
Molecular mimicry in action
When a molecule in one organism structurally resembles a molecule in another organism, usually from another species, this is called molecular mimicry. Especially when comparing animal proteins from specific organs with their counterparts in the human body, for example a pig’s thyroid protein and a human thyroid protein, the molecular resemblance, according to McDougall, is very strong.
While certain organs or glands like the thyroid are usually not allowed to enter food products, McDougall argues that the reality in slaughterhouses might be rather different. Instead of “wasting” animal tissues, they may well end up in products like sausages and hot dogs, where people do not really tend to care what is in them anyway.
Apart from that, a very similar protein does not necessarily have to come from the same animal organ as the human organ that later gets attacked. In fact, beta-casein, a protein found in dairy products, shows a strong resemblance to the pancreatic beta cells, with 17 corresponding amino acids.
The body’s immune system therefore then not only attacks beta-casein but also the pancreatic beta cells, which are responsible for producing insulin. Without these cells, the body can no longer produce its own insulin. This condition is known as type 1 diabetes.
For a more detailed explanation and an exploration of other autoimmune diseases in this context, I recommend Dr. McDougall’s presentation on the topic:
Other plant-based perspectives on autoimmune disease
While Dr. McDougall presents one of the more direct and far-reaching theories, other plant-based physicians also emphasise the role of diet in the development and progression of chronic disease, including autoimmune conditions.
Dr. T. Colin Campbell, known for the China Study, has long argued that animal protein plays a central role in promoting disease processes in the body. Although his work does not focus specifically on autoimmune disease, he highlights how diet can influence immune function and inflammation on a systemic level.
Dr. Caldwell Esselstyn, who is best known for his work on heart disease, similarly emphasises the damaging effects of animal-based foods on the body. His approach focuses on restoring health through a whole-food, plant-based diet, which he associates with reduced inflammation and improved overall function.
Other physicians, such as Dr. Neal Barnard and Dr. Joel Fuhrman, also support the idea that diet plays a critical role in immune health. Their work suggests that plant-based nutrition can help reduce inflammation and may improve symptoms in certain autoimmune conditions, even if they do not always explain it through the same mechanisms as McDougall.
