Do Wild Chimps get Autoimmune?

[TLDR: Let's look into the genesis of autoimmune disease in the human gut and in human history. If you're ready to reverse your vitiligo or other autoimmune disease, be sure to check out the new course here. Use code NOV23 at checkout for a 10% discount.]

All disease begins in the gut. So the great Hippocrates told us more than 2,000 years ago. In the case of autoimmune disease, he couldn’t have been more right.

There are a couple of competing theories about how autoimmune disease happens. As this paper rightfully points out, not enough time and money has been spent in researching autoimmune disease. So our understanding is woefully incomplete.

Even with this incomplete understanding, we can conclude that vitiligo and other autoimmune disease begins in the gut. 

In order to understand this point, let's take a moment to understand our gut. What does the human digestive system look like next to the digestive system of our closest existent relative, the chimpanzee?

To the layperson’s eye these images may look similar, but let’s focus on a few differences here:

1. The human stomach is smaller.

2. The human small intestine is much longer (5.5 meters vs 1.5 meters)

3. At the top of the large intestine, chimpanzees (and other primates) have a cecum. In humans this has shrunk to be what’s called a vestigial organ (meaning we think it’s not really used anymore) called the appendix. 

4. The top of the large intestine is thicker and the large intestine as a whole is longer in chimps.

There is also one difference that won’t show up in the diagram and that’s the fact that the human stomach is much more acidic than the stomachs of other primates. Chimps have a stomach acidity of around 4, making their stomachs roughly 500x less acidic than the human pH level of 1.5. Why would our stomachs be so much more acidic than that of our closest existing relatives? We don't fully understand the answer to that question and comparative anatomy does not lend itself to proof by randomised controlled trial. But we can take some educated guesses.

Smaller stomachs probably mean that humans were eating more nutrient dense foods. Those were almost certainly animal foods - if you think early humans were eating kale, remember that kale and most of the other fruits and vegetables didn’t exist until very recently. The plant foods that did exist were either highly seasonal (berries and other fruits) or lacking in nutrients (dense, fibrous tubers).

Because we had to get nutrition out of a smaller meal, our stomach acidity had to increase. Now one would surmise that the acidity would increase to the level of carnivores, but our stomachs are more acidic than even those of lion and more closely resemble the pH of scavengers. That would indicate that at some point we had to get used to eating meat that today we might consider “spoilt”. The high pH is necessary to get rid of potentially pathogenic bacteria. It's possible that these adaptations explain the fact that many people enjoy the taste of aged and cured meats. 

The last thing I’ll point out is that we as humans have lost our cecum, which is a crucial organ for primates who rely on bacteria to help derive some nutrition from plant foods. Herbivores, we now know, do eat plants but a lot of their energy comes when beneficial bacteria in their digestive tract turn those plants into fatty acids. For primates, the place where the bacteria live is called the cecum. Humans don’t have a cecum, and while we can ferment some fibrous foods into fatty acids, it’s not clear how much of this gets reabsorbed from the large intestine. In other words we may be fermenting some plant matter, but it’s unclear if we get the benefits. We certainly don’t get the benefits of vitamin B12 synthesised by bacteria, which is also produced in the large intestine but cannot be reabsorbed.

Human digestion largely happens at the front end. Highly nutritious (animal based) foods are broken down into their component parts by a very acidic stomach and then digested by the small intestine. Any remaining plant matter passes through the system largely undigested until it reaches the large intestine. There fermentation takes place and possibly some re-uptake of nutrients. But much of the plant matter remains undigested or partially digested and is excreted that way.

This is just some common sense hypothesising based on the differences in the human digestive tract. It looks as though we were made to eat mostly meat with perhaps some plant matter. If you find a human population that’s eating mostly plants during the pre-history period, chances are that population is suffering. They’re having a famine. There are a couple of papers published on dentition which show that when early humans ate more plants they got cavities. Those are the first incidents of cavities anywhere in the fossil record.

So what happens when something changes? A society built on urbanisation, farming and mass enslavement for example. Well that’s what happens in ancient Egypt. And it also looks as though ancient Egypt may have had the first recorded cases of autoimmune disease. Now we’re not going to know if they had vitiligo because that doesn’t show up in the fossil record or even in mummies. But we do see some cases of what looks like rheumatoid arthritis in fossils and mummies. We also know that ancient Egyptians were developing widespread heart disease and seem to have been dying of heart disease as well.

Why should that be happening? Well it turns out that it’s not just any kind of undigested plant matter that can cause autoimmune disease. There are some things that are guiltier than others. At the top of the list is the gliadin protein found in wheat and a few other grains. Wheat was the staple food of ancient Egypt, so it’s no coincidence that this appears to be the culture that invented autoimmune disease.

From this it does not follow that wheat causes autoimmune disease. Plenty of people can eat wheat and be fine with it. But in the modern food environment it’s not just wheat. There are a lot of things that we’re exposed to that our ancestors would never have seen - things as seemingly innocuous as watermelon in the wintertime or as insidious as atmospheric lead - that are adding fuel to the fire of autoimmune disease. 

Most importantly, we've all been told for the last 40 years that plant-based diets are healthy diets. In other words, eat like a chimp despite the fact that you don't have a chimp's digestive system. Gliadin is a plant protein. It's a lectin, a type of anti-nutrient found in nearly all plant foods. Chimps and other herbivores have digestive systems that can detoxify these plant toxins. Humans do as well, but it's a much more limited system. When we overdo the plant foods or eat a majority of our food as plant foods, we can trigger an autoimmune response. When we eat like a human - as close to the diets that humans evolved to eat as possible - we don't have these issues. Sometimes we can reverse them. 

In the next post I'll go into those drivers - inflammation and allergens - in more detail. For now, if you'd like to start to tackle your own autoimmune symptoms, do sign up for the reversing vitiligo and other autoimmune disease here. Use code NOV23 for a 10% discount until the end of the month.