The Factor Omitted in Paleo Theories: Parasites

Interlibrary loan sent me a copy of the book, Mummies, Diseases and Ancient Cultures recommended by a knowledgeable blog commentator, but unfortunately it turned out to be the first edition published in 1980 not the updated one from 1998. I'm using an extended ILL feature to request the newer version, but meanwhile I read through the first edition and found it fascinating.

Relevant to the topic of my blog here was one theme that stood out in analysis of all the ancient bodies that had been preserved through time: Ancient people, no matter what time period they lived in or where they lived, carried a significant load of parasites.

The parasites most commonly found in these munmies included hookworms, tape worms and the roundworms that cause trichanosis. Besides sickening us, these parasites can make a significant difference in how we metabolize foods.

The tapeworm, for example, allows people infected with it to live out the dubious fantasy of "eat all you want and never gain weight." Unfortunately, when this happens in a situation where the food supply is marginal--i.e. just about everywhere on earth before the 20th century--worm infestation can predispose people to starve to death.

The roundworms lay eggs in human muscle, which probably produces inflammation, though they also can infect nerves and the brain. In either case, they have a strong effect on metabolism.

Parasites get into our bodies in many ways. Some come from eating meat that hasn't been thoroughly cooked. Some are carried in water where other animals have defecated. Some enter the body from the soil. Others are transmitted by insect bites.

Because parasites were such a common feature of life until very recently, it makes sense that our bodies are highly adapted to live with them. And because the loss of the usual human parasites load is so very recent, some scientists who study the development of the human immune system speculate that the current explosion of autoimmune disease is partly caused by changes in the way that the immune system develops in children whose immune cells don't encounter parasites early in life.

This theory was discussed in detail in the book, Good Germs, Bad Germs: Health and Survival in a Bacterial World, by Jessica Snyder Sachs.

However, while there may be something to this theory, there are plenty of other factors besides parasite exposure that also explain the increase in autoimmune diseases. And a big problem with the parasite explanation is that it doesn't explain why this explosion in diagnoses only kicked in about twenty years ago.

My belief is that the invasion of our food supply by soy protein and its ability to damage the gut and make it permeable to proteins like gluten is probably a better explanation for the changes seen in the past generation. I've discussed that theory HERE.

Still, there is no question that the elimination of parasites from our system is a huge change in human health and one that only took place in developed nations during the past century.

Caleb Finch, a gerontologist from the University of Southern California (USC), has come up with an intriguing theory, published in December issue of Proceedings of the National Academy of Sciences that links the loss of our parasite burden with the increase in heart disease and Alzheimers.

His theory explains the fact that humans have much longer natural lifespans than apes, as a result of their having developed new gene variants that allow them to tolerate the higher burden of inflammation that comes with eating a meat-rich diet.

You can read the text of the press release describing this study sent out by USC displayed here:

Science Daily: Why Humans Outlive Apes: Human Genes Have Adapted to Inflammation, but We Are More Susceptible to Diseases of Aging

It quotes Finch as saying:

"Over time, ingestion of red meat, particularly raw meat infected with parasites in the era before cooking, stimulates chronic inflammation that leads to some of the common diseases of aging,"

From reading the Mummies book, I would correct this statement, because the data reported in the mummies book makes it very clear that ancient meat-eating humans who did cook their food still carried a high load of meat-borne intestinal and muscle parasites.

But Finch goes on to explain that one way humans adapted genetically that allowed them to flourish with a higher burden of meat-borne parasites is by evolving a human-unique form of Apo(E).

Finch is quoted as saying,

In addition to differences in diets between species of primates, humans evolved unique variants in a cholesterol transporting gene, apolipoprotein E, which also regulates inflammation and many aspects of aging in the brain and arteries.

Other primates who do not have the human forms of Apo(E)develop heart disease very quickly if they eat diets rich in meat, an argument that is often cited by those promoting vegetarian diets.

Still, unlike gorillas who develop heart disease in just a few years after adopting a meat rich diet, humans eating meat-rich diets do not develop heart disease until they are in middle age-- after they have reproduced, which Finch links to the human-only Apo(E) variant. And later-onset heart disease because it happens after reproduction does not impact evolution.

Finch does not pursue this point, but it strikes me that this argument suggests that the loss of the usual human parasite load may also partially explain why the incidence of heart disease has increased over the past century--the period in which humans for the first time cleaned up water supplies and eliminated wild meats with their high parasite load from their diets.

It is possible that when the immune system is not kept busy dealing with a high level of inflammation caused by invading parasites it is more apt to attack cardiac tissue. Recent research suggests very strongly that heart disease is an inflammatory condition. There are also intriguing hints that morbid obesity may be linked to inflamed fat tissue.

None of these theories are fully fleshed out. Though Finch's finding that only humans have the special forms of Apo(E) required for primates to metabolize meats should give us another reason to ignore ALL diet research performed in rodents or other non-human species because these other species do not carry the human adaptations to meat eating that Finch suggests are a large part of why humans have evolved so successfully.

Beyond the changes that allow us to eat parasite-infested meat safely, there are probably human physiological adaptations to parasites that impact on our ability to store fat in an environment were we are competing with parasites for the nutrients in our food.

This suggests to me that followers of the so-called Paleo diet cannot faithfully reproduce the supposed health effects of that diet unless they have taken on the load of intestinal worms early in life and allowed them to mold their immune systems and other physiological parameters.

Even adding these worms in mid-life won't help because, as Sachs' book explains, the balance of the kinds of T cells produced by the immune system throughout life seems to be shaped by the antibodies transmitted from the mother (infected with parasites in a true Paleo state) and the organisms the young creature encounters early in life.

Without a gut full of worms no one is eating a true Paleo Diet. Which is another reason to avoid extremism in dietary theory and to eat a diet that resembles that which your long lived ancestors in the past 150 years were eating.

The Colonial era graveyards in rural New England where I live are filled with graves of people who lived into their late 80s and 90s. Those who died young typically died of infectious disease, child birth, or, surprisingly frequently, fire and drowning.

We know a great deal about their diet. It was made up of fresh meat in summer and fall, salty preserved ham, salt beef, and lots of salt cod the rest of the year, dried fruit, corn meal, wheat, squash, turnips, and potatoes, preserves made with sugar, and milk, butter and cheese.