The Science of Paleo

Is the Paleo diet concept scientifically valid?

If your primary source of information about Paleolithic nutrition is the mainstream media, then chances are you’ve been led to believe that the answer to that question is no. If your primary source is the scientific literature, however, then you’ve undoubtedly realised that the true answer is yes, and that much of what is written and said about the original human diet outside of the realm of science finds its origin in the minds of ill-informed and biased individuals who don’t know much about evolutionary health promotion, ancestral human diets, or Darwinian medicine.

The fact is that no other diet has scientific roots that are as deep and strong as that of the original human diet. Those who get their information about Paleolithic nutrition primarily from blogs, social media, and newspapers and/or have repeatedly heard government-supported nutritional authorities say that the official dietary guidelines are based on the best available scientific evidence, may find that hard to believe, but it is in fact the truth.

The thing that most clearly separates the scientific foundation of the Paleolithic diet from that of other diets is its unique diversity of different building blocks. Not only does it contain many clinical trials and observational studies, but it also has a lot of other forms of research incorporated into it. In this article, I thought we’d have a look at 8 of the most important constituents of the scientific foundation on which the Paleo diet is built.

the-8-scientific pillars-of-the-paleolithic-diet

1. Paleontological research

Among evolutionary biologist and paleontologists, it’s well known that the Agricultural Revolution unfavorable affected the health of Homo sapiens. The human population grew rapidly following the dawn of agriculture; however, that doesn’t necessarily mean that people got healthier. On the contrary, examinations of fossil remains have revealed that Neolithic humans who had taken up Agriculture didn’t grow to be as strong and tall as Paleolithic hunter-gatherers (1, 2, 3, 4). Moreover, they were more prone to develop tooth decay, malocclusion, periodontal disease, and many other diet-related health problems (1, 2, 3, 4, 5). This isn’t surprising, seeing as they ate a less diverse and starchier diet than their preagricultural forebears.

These findings are very consistent, in the sense that whenever and wherever people have made the transition from eating a hunter-gatherer style diet to eating a more simplistic diet that is largely built up of grains and/or dairy foods, adverse health outcomes have been a part of the “transition package”.3, 4 The dietary shift that accompanied agriculture was not solely responsible for bringing about the decline in the human health condition that accompanied the first major epidemiological transition in human history; however, it was undoubtedly a major contributing factor.

2. Genetics research

The natural question that arises from the previous section is: Have we overcome the health problems that accompanied the Agricultural Revolution?

The short answer to this question is no. Over the past millennia, certain diet-related genetic adaptations have spread within some human populations and equipped people with an enhanced ability to digest and metabolize various forms of modern foods. For example, within certain populations that have a long history of eating starchy diets, natural selection has driven up the copy number of the AMY1A gene (6), a gene that codes for an enzyme that is involved in carbohydrate digestion.

With that said, we know for certain that we’re not well adapted to consume grains and dairy foods (1, 7, 8, 9). The adaption that has occurred is only partial. This statement is supported by the fact that we, just like our ancestors, are prone to develop tooth decay, bone mineral disorders, and many other health problems if we consume a lot of grains and/or dairy foods (7, 10, 11, 12, 13, 14).

Foods are composed of a great variety of different nutrients and other compounds. Perhaps needless to say, if an animal species suddenly incorporates a completely new food group into its diet, just one or a couple of smaller genetic changes are not going to fully accommodate for that dietary change.

The key thing to remember is that natural selection doesn’t necessarily “make” organisms healthier, happier, or more long-lived. Rather, Darwinian evolution occurs as a result of variation in reproductive success. A lot of people can eat and digest milk and grains and not experience any acute gastrointestinal issues or major reproductive impairments; however, that doesn’t necessarily mean that it’s healthy for these individuals to consume those foods.

The bottom line is that we are still largely hunter-gatherers from a genetic perspective (3, 15).

3. Clinical research

Some people seem to be under the impression that very few or no Randomized Clinical Trials (RCTs) have looked into the therapeutic potential of hunter-gatherer style diets. This is simply not true. Over the past decade, several clinical trials on Paleolithic nutrition have been published (16, 17, 18, 19, 20), some of which were conducted by the legendary researcher Staffan Lindeberg and his research team.

These studies have shown beyond any doubt that the Paleolithic diet is a very healthy diet. Some of the studies have a fairly small sample size, however, as a whole, I would say that the clinical evidence is fairly convincing. The results from the studies in this area all point in the same direction, in the sense that they suggest that Paleo-style diets are highly efficacious in the treatment of various metabolic and inflammation-driven disorders and produce greater health improvements than “prudent” diets such as the Diabetes diet. This is exactly what one would expect to see, seeing as the Paleolithic diet has certain unique characteristics that separate it from other diets (something we’ll talk about later).

Some people seem to think that a solid body of research shows that it’s healthy to eat a lot of whole grains. This is simply not true. Several RCTs and meta-analyses have indeed shown that the consumption of whole grains is associated with various positive health outcomes (21, 22), but these studies have a major limitation, and that is that they don’t compare prudent grain-free diets (e.g., Paleo-style diets) with diets rich in whole grains; rather, they compare the health effects of whole grain consumption with the health effects of refined grain consumption or the consumption of some other unhealthy food or a flexible diet. Hence, they by no means prove that it’s healthier to eat a diet rich in whole grains than a prudent diet that doesn’t contain any grains at all.

I think one of the major problems that plague the field of nutrition today is that there’s too much focus on clinical research. Some people seem to be under the impression that everything needs to be tested in RCTs and that the only evidence that truly matters is the evidence that is derived from strictly controlled, double-blinded studies.

I disagree with this perspective. As I see it, the clinical research is merely the icing on the cake. This icing is not much use if we don’t have a cake. Personally, I prefer a cake that is composed of a variety of scientific evidence, including evidence derived from research conducted within the disciplines I talk about in today’s article.

4. Morphological research

You can learn a lot about what an animal should eat by studying the structural composition of that animal. Some animals are clearly designed to consume a plant-rich diet. The cow for example has a large intestinal system in which trillions of microorganisms are hard at work, turning the cellulose-rich plants the cow is eating into fatty acids and other end-products. Other animals, such as the lion, on the other hand, don’t have a huge fermentation chamber, but largely rely mostly on its own genes to break down the foods they’re eating.

Typically, animals that eat a lot of plant matter has larger guts than those that eat more animal based diets, which is not surprising, seeing as the latter diets tend to be more calorically dense and less bulky than the former. Moreover, plant-eating animals rely on gut microorganisms to break down many of the food substances they take in and therefore need a “chamber” where their gut microbes can live and do their fermentative work.

Another thing that separates animals that eat a lot of plants from those that eat mostly meat is that the latter tend to have more acidic stomachs (23). This isn’t surprising, seeing as an acidic stomach acts like a barrier against food-borne pathogens and also because hydrochloric acid plays a role in protein digestion.

Where does our species, Homo sapiens, fit into all of this? We’re somewhere in the middle between the lion and cow mentioned earlier. We’re not wired exclusively for meat eating; however, we’re not wired exclusively for plant consumption either. We’re omnivorous.

The thing that seems to elude some vegans and vegetarians is that a large body of evidence shows that our ancestors transitioned over from eating a largely plant based diet to eating a higher quality, more meat-based diet some ~ 2.5-3 million years ago (3, 24). This idea is not only supported by archeological research (e.g., examinations of stone tools), but also by studies looking into the evolution of the human body. As more meat, and perhaps also other energy-rich foods such as tubers, were incorporated into the human diet, the large intestines of our ancestors started shrinking (25). One doesn’t have to be a genius to understand why, all that’s needed is a basic understanding of nutrition and evolution.

Animal source foods are primarily digested in the upper parts of our digestive systems, in particular the small intestine. Fibrous plant foods on the other hand are primarily broken down by gut bacteria that dwell deep down in our large intestines. You don’t need a huge large intestine to break down a meat-heavy diet; hence, it’s not surprising that our ancestors’ colons shrank as a result of selective processes when they started eating more animal source foods. Not only has the human colon gotten smaller throughout our evolutionary history, but the human stomach also seems to have gotten more acidic (23), which is another indication that our ancestors gradually started eating more meat.

The morphological research clearly refutes the notion that we are designed to eat exclusively meat or plants. We’re clearly designed to eat a mix of the two. Moreover, it’s important to point out that none of the animal species that are in close proximity to us on the tree of life consume the milk of another animal or eat a grain-based diet. We don’t really know for certain exactly what the gut of a mammal that is designed to eat a diet rich in grains, dairy foods, and processed foods looks like, seeing as no such mammal exists.

5. Nutritional research

RCTs, observational studies (which we’ll talk a little about later on), and systematic reviews and meta-analyses are far from the only types of studies that are useful for learning about human nutrition. Over the most recent centuries, we humans have made great strides forward when it comes to elucidating the composition and characteristics of the food we eat. We’ve “broken down” various types of foodstuffs and given names – vitamin C, protein, fiber and so on – to their constituent parts. We’ve also looked into how the consumption of different types of foods affects various metabolic and inflammatory parameters.

This brings us over to something that’s really fascinating about the original human diet, and that is that it has certain nutritional characteristics that clearly separate it from “modern diets” (9, 10, 26). Among other things, the foods that were a part of the Paleolithic diet have a low-moderate energy density, high satiety index score (27), and high nutrient density (28). Moreover, when compared with cereal grains, they all have a much lower carbohydrate density, and when compared to fatty dairy foods (e.g., butter, cream, cheese), they have a much lower content of saturated fat and total fat. Furthermore, when compared with cereal grains and dairy foods, Paleo foods are low in antinutrients, hormones, and/or other potentially problematic compounds. Hence, it’s not surprising that the Paleo diet is so therapeutic.

A large body of evidence shows that these discrepancies between the original human diet and modern diets are at the root of many of the diseases and health problems that plague the modern man (89, 29, 30).

6. Mammalian research

As pointed out earlier, it’s abnormal for a mammal to eat a diet that contains large quantities of grains and dairy foods. The thing that eludes a lot of people is that the milk of each mammalian species that is present here on Earth was specifically designed, via natural selection, to support the growth and development of the young of that species.

Milk is not just this white liquid that is rich in calcium, protein, and fat. Rather, it is a very special type of food that has potent immunomodulatory properties and contains a variety of compounds that up until very recently were not a part of the adult human diet. From an evolutionary perspective, it’s very abnormal for a human adult to drink milk. Hence, it’s not surprising that the consumption of milk has been found to be associated with a variety of adverse health effects (31).

As pointed out earlier, the fact that some people can digest milk without experiencing gastrointestinal distress does not mean that it’s necessarily healthy for these folks to drink milk. Some of the issues with milk can be remedied via fermentation; however, others remain pretty much regardless of the type of processing technique that is used.

The story is somewhat similar for grains. None of the free-living species on this Earth that we most closely relate to consume a grain-heavy diet. Domesticated animals on the other hand are often given grains. This is part of the reason why they are not as healthy as their wild counterparts. This simple fact, that domesticated animals that are fed grain-heavy diets tend to get fat and sick, should get us to think twice about eating a lot grains. Obviously, our biology and physiology differ a lot from that of for example a cow; however, we’re no different from the cow in that we too get sick and fat if we eat a diet that matches poorly with our evolved biology.

Unlike animals, plants can’t run away from predators (e.g., mammals that want to eat them). They have evolved other ways of defending themselves. One of the things they do is that they produce metabolites that are toxic to their “foes”. Some plant foods, such as cereal grains, are particularly rich in these types of secondary metabolites, some of which are capable of disrupting various physiological processes within the human body (1, 7).

It’s believed that our primal ancestors ate a great diversity of different plants; hence, they didn’t expose themselves to very large quantities of just one or a couple of secondary metabolites, seeing as different plants produce different toxins. Many early farmers and contemporary humans on the other hand consume large quantities of just one or a couple of plant species. Not only that, but many of the plant species that we consume today have only been a part of the human diet for a short time, meaning that we may not have evolved a way to neutralize the toxins they produce.

A lot of mainstream nutritionists seem to pay little attention to these things. Instead of looking at how things work in nature, they spend all their time sifting through clinical studies and government-produced nutritional guidelines. This is unfortunate, because it’s impossible to make sense of what different organisms are designed to eat if one doesn’t look into the role that different foods play in the diets of various wild animals and the interactions that take place between organisms and their nutritional environment.

7. Anthropological research

Over the most recent centuries, many explorers and scientists have visited non-westernized, traditional societies that live or lived largely cut off from the modernized world. Some of these travelers, such as the legendary Weston A. Price, documented the health and physical fitness condition of the people they met on their travels. Whereas some of the reports from these travelers are fairly superficial and subjective and contain limited detail, others are based on comprehensive health examinations. These latter reports are those that evolutionary nutritionists such as myself are the most interested in.

The most striking thing about the studies, books, and reports that cover the health of traditional populations is that they pretty much all indicate that non-westernized people who consume hunter-gatherer style diets are largely free of chronic diseases such as diabetes, colon cancer, and celiac disease (10, 32, 33, 34, 35). Moreover, when compared to westerners, they are in much better cardiovascular and metabolic health, as measured via assessments of various blood markers (10, 32, 33, 35). For example, when Staffan Lindeberg and his colleagues visited Kitava in 1989, an Island in Papua New Guinea, they found that the people who lived there were in excellent health. Acne, cancer, and heart disease were all but absent and nobody was overweight (36).

Some non-westernized people who consume traditional diets that contain some non-Paleo foods have also been shown to be fairly healthy; however, in general, it seems that there is a gradual decline towards worse and worse health as we move from hunter-gatherer type diet towards western-style diets.

Perhaps needless to say, other factors besides diet are important up in all of this. For example, most traditional people are quite physically active and spend a lot of time outdoors, which cannot be said for the typical westerner. Hence, these types of studies don’t prove causality. With that said, there is no doubt that one of the primary reasons why the Kitavans and other traditional, non-westernized people are so healthy is that they eat a healthy diet. This statement is supported by the fact that the results from the studies in this area all point in the same direction and that every time a group of traditional people transitions over to eating a more westernized diet, negative health outcomes follow (10, 34).

8. Microbiome research

The trillions of microorganisms that colonize our bodies have a profound impact on our health and well-being. Among other things, they regulate our immune systems, shape our behavior and thoughts, and break down some of the food we eat. Given this, it’s obviously important that we take good care of the friendly bugs that colonize our bodies, as well as do what we can to keep unfriendly critters at bay.

Over the past decade I’ve spent a significant amount of time reading up on the human microbiome, and I’ve put a lot of thought into the question of what we should eat to optimize the diversity and stability of our microbiotas. One of the most important things I’ve learned throughout my decade-long travels through the world of the microbiome is that “modern foods” affect the composition of the human microbiota in such a way that the health of the human host is negatively affected.

This statement is supported by a big pile of scientific evidence. Several studies have shown that the consumption of very sugary and/or starchy foods, including highly processed foods and both refined and whole grains, induces the growth of proinflammatory oral bacteria such as Streptococcus mutans (12, 13, 14). Furthermore, a long list of studies have found that the consumption of foods that have a very high fat density, such as cream, sets the stage for translocation of bacterial endotxoins from the small intestine into systemic circulation, endotoxemia, and chronic inflammation (35, 36, 37). Other types of evolutionarily novel foodstuffs, including whey protein supplements, can also disrupt the microbiota (38).

When we think about it, it’s not really surprising that modern foods are capable of altering our microbiotas in such a way that our health suffers. Natural selection acts to adapt organisms to their environment. Microbes are an important part of our environment; hence, it goes without saying that microbes constitute one of the selective pressures that have acted – and continue to act – upon the human genome.

Up until very recently, all humans on this planet ate a hunter-gatherer type diet. Throughout evolutionary time, the human biology has evolved to match well with the type of microbiota that is produced by a Paleo-style diet.

When our ancestors’ diets changed with the Agricultural Revolution, their microbiotas also changed (39, 40). The grain-heavy diet they started eating produced microbiotas that matched poorly with our ancestors’ genomes; a statement supported by the fact that dental caries and periodontal diseases were more common among early farmers than among preagricultural humans (13).

Just like our Neolithic forebears, our oral health suffers if we eat a lot of starchy and/or sugary foods. This clearly suggests that our bodies are not very fond of the type of microbiota that modern diets produce.

It’s well established that the human microbiome has changed a lot over the past 10.000 years (41, 42). These changes can partly be attributed to changes in the human diet. Highly processed foods are obviously particularly problematic; however, we shouldn’t overlook the fact that many types of grain and milk based foods also cause problems. Whole grains contain fiber; however, much of this fiber is of the insoluble type and is not accessed by colonic bacteria. Moreover, as pointed out earlier, the consumption of grains have been shown to adversely affect dental health via its effect on the oral microbiota.


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