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A review of the evolutionary claims in the Paleo Diet

The Paleo diet trend was kicked off with the publication of a book by Dr. Cordain published in 2002. Since then it’s popularity has increased steadily. Dr. Cordain believes that by eating as he believes our ancestors ate you can lose weight, and cure many diseases. Despite Dr. Cordain’s claims of expertise on Paleolithic diet, heath, and nutrition the majority of his claims are suspicious at best. The majority of the book relies on the appeal to nature fallacy whereby Dr. Cordain repeatedly claims that the only natural and safe diet for humans is the way our hominid ancestors allegedly ate. In order to understand the problem with many of Dr. Cordain’s statements you must first understand human evolution.

The Paleolithic period, which means Old Stone Age began approximately 2.5 million years ago when hominids began making stone tools. It ended approximately 10,000 years ago when the Mesolithic, or Middle Stone Age, began with the advent of agriculture in the archaeological record. The Paleolithic period can be further broken into the Lower Paleolithic period that lasted from 2.5 mya (million years ago) to approximately 200,000 ya (years ago).  For much of the Lower Paleolithic period stone technology was quite simple, and did not change much despite significant changes in hominid species and their brain capacity. Approximately 200,000 ya the Upper Paleolithic began when our species, Homo sapiens, evolved. Now this distinction is not merely human ego, but is based on the more advanced stone technology that humans displayed compared to other hominid species.

During the Paleolithic hominids learned to control fire, and it is thought that the first signs of human culture date back to the Paleolithic. Archaeological sites from this time are very rare. Any hominid remains from this time consist solely of fossilized skeletons that are fragmentary and often quite degraded.The archaeological evidence suggests that Homo erectus was the first species to be able to control fire, and therefore to begin cooking food. This is a very important factor in human evolution. It has long been known that eating meat was important to human evolution, particularly in allowing our brains to grow to unprecedented size and complexity compared to our body size.

Our hominid ancestors most likely started out as scavengers before learning to hunt animals for food. However there is another aspect of meat eating whose importance is often under estimated, and that is the ability to cook the meat and other foods so that the nutrients are more easily absorbed. As cooking developed we see morphological changes such as decreased molar and mandible size as large jaws and teeth were no longer necessary to process tough food.

It is undeniable that humans evolved by eating an omnivorous and very adaptable diet. The evidence for this is written all over our bodies if you know how to read it. Perhaps the most easily identified evidence of our omnivorous origins lies in our teeth. We have teeth that are designed for chewing plant matter as well as consuming meat. As tooth morphology is almost completely controlled by genetic rather than environmental factors it is very slow to change and an excellent source of information about human evolution.

The consumption of meat was undeniably a very important nutritional source for hominids, however Dr. Cordain is incorrect in overstating how frequently hominids and early humans ate meat. Archaeological evidence suggests that most hominid species and archaic Homo sapiens were primarily vegetarian with meat being an occasional dietary supplement when available. This is supported by studies of modern hunter-gatherer populations.

Now it is important to understand that direct comparisons between modern hunter-gatherer populations and prehistoric populations are not possible. The environment has changed dramatically since the Paleolithic, even since the Mesolithic the environment has undergone rapid change. This means that the environments that modern hunter-gatherers live in is not necessarily similar to the environment that prehistoric populations lived in. Additionally modern hunter-gatherer populations have been pushed to areas that are not conducive to agriculture, while prehistoric populations would have lived in all environments. Yet that direct comparison is something Dr. Cordain attempts to do on several occasions.

Studies of modern hunter-gatherer populations are useful, but it is very important to remember that there is no single dietary pattern than hunter-gatherer’s utilize. They are known to be very flexible in their food sources. Modern population’s diets range from extremes such as the Inuit whose diet is predominantly meat based, to the predominantly vegetarian !Kung. Some hunter-gatherer populations are also well known to consume large quantities of starchy vegetables that according to the Paleo diet they should not be consuming.

Dr. Cordain states that during the Paleolithic humans had a longer life span, did not suffer from tooth decay, did not have “modern” diseases and were taller than in the Mesolithic and later periods. In order to examine these claims you need to understand a little bit about biological anthropology, which is the study of human and hominid skeletal remains. It is generally accepted that only a very small proportion of diseases leave a mark on the skeleton, and very few of these are specific enough to diagnose. As the majority of our bodies are made of soft tissue, therefore the majority of our illnesses are found in the soft tissue. Due to how long it has been since the Paleolithic no soft tissue has ever been found from this time. That means the only way to assess health is through the skeletons. Now we can determine their estimated height, age, and the sex of adults if the skeletal remains are complete enough, but this becomes more difficult to accurately assess as the remains become more fragmentary. As there is no soft tissue we cannot determine if the individual had diseases such as heart disease or diabetes, nor can we tell if they were obese as there is no consensus on how to identify obesity in the skeletal record at this time. We can look at indicators of health and nutrition called non-specific stress indicators, such as bone porosity or interruptions of dental enamel formation in childhood.

Linear Enamel Hypoplasia, an enamel defect that can be caused by malnutrition or disease in childhood. Source: The Museum of London

The average stature of a population has cycled many times throughout history. Our adult height is affected by a combination of factors including genetics, nutrition and health. In some populations stature and general health did decrease after the advent of agriculture, but to associate that strictly with nutrition would be incorrect. With the advent of agriculture we suddenly had large populations living in the same place for extended periods of time, and there was not exactly good hygiene or sanitation. The communicable disease load increased dramatically as populations grew. In some areas malnutrition also increased, but this trend is not universal. There is a pattern of negative affects on health in the archaeological record as agriculture was adopted. However not all populations that transitioned from being a hunter-gatherer society to agricultural society  experienced this decline. In particular it does not appear to be associated with societies that began depending on wet-rice agriculture. The decline in health is particularly noticeable in societies that depended on maize as their main crop.

Life span is another factor that is harder to determine. Once an individual reaches adulthood it becomes more difficult and less accurate to determine their age at death based on the skeleton. It is not impossible, but the age frames become wider than with children that can be accurately aged based on tooth eruption patterns and bone growth. The average life span of a population is difficult to estimate. In the past there were high rates of child and infant mortality. We do not know how high these rates were in the Paleolithic as the bones of children are more delicate than the bones of adults and do not preserve as well. We do know that if one survived into adult hood the next biggest threats to their lives were infection from injury, and for women childbirth. This is one of the reasons that in the archaeological record we see more men surviving into old age than women. These death patterns also skew the population’s average age at death downward. The fact is  the archaeological record shows that the average age of death for humans and hominids in any period was far shorter than it is today. While some individuals did survive into old age, even during the Paleolithic the average lifespan of an individual was what we would not consider not quite middle age.

The archaeological record does not support the claim that hominids and humans prior to agriculture did not have tooth decay, or caries. Neanderthals lived during only during the Paleolithic with the last Neanderthals dying out on Gibraltar approximately 28,000 ya. The skeletal remains of Neanderthals and other hominid species show signs of periodontal disease, and caries. While we do not know the rate at which caries and dental disase were present in the Paleolithic, we do have evidence that it was at lower rates than in societies that practice agriculture. In this Dr. Cordain is correct that agriculture had a negative impact on our health.

Dr. Cordain repeatedly claims that the so-called modern diseases such as cancer, diabetes and autoimmune diseases did not exist prior to agriculture. The evidence does not support this either. The oldest known case of cancer in hominids is a 1.7 mya osteosarcoma found in the metatarsal from an unknown hominid species. Cancer is found across species, therefore it is likely that cancers in hominids are older than this, but we do not have evidence to conclusively state this.

We do not know when the first case of heart disease, diabetes or autoimmune disease occurred based on skeletal material and that is where we must start looking at genes. After death the DNA in the body degrades until it is impossible to be extracted for analysis. At this time it is only possible to extract DNA in skeletal remains up to 30,000 ya, therefore Neanderthals are the only reliable source of non-human hominid DNA. The Neanderthal genome was sequenced several years ago and has provided a wealth of information. We now know that they had the genes for some autoimmune diseases such as lupus and Crohn’s disease. They also had genes that indicate a predisposition to several diseases that are considered modern diseases. These include type 2 diabetes, heart attacks, heart disease, and depression. This is contradicts Dr. Cordain’s claim that eating his version of a Paleolithic diet will cure or prevent these diseases as they are complex disease that include both genetic and environmental factors.

In 1991 one of the oldest mummified human remains were found in the Ötzal Alps. Ötzi, as he is known, dates back to the Neolithic (New Stone Age) approximately 5,300 ya. Ötzi was found in a glacier, which preserved his body remarkably well. Analyses of his genes show a predisposition to heart disease, and the presence of the world’s oldest case of Lyme disease. A CT scan confirmed the diagnosis of atherosclerosis. Now agriculture was present in the Neolithic and in fact Ötzi’s last meal did contain some unleavened bread however; studies of remains including those from hunter-gatherer societies suggest that atherosclerosis was prevalent in antiquity contrary to Dr. Cordain’s claims that it is only caused by agriculture.

A reconstruction of what Ötzi would looked like at the time of his death. Source: The South Tyrol Museum of Archaeology

The Paleo Diet does have some good points about choosing lean meats over fatty meats, reducing salt and sugar consumption,  and increasing fruit and vegetable consumption. These are all recommendations routinely made by dietitians. However it also states that all grains, legumes and dairy should be avoided. Dr. Cordain repeatedly claims that our hominid ancestors did not eat grains or dairy, and therefore we should not either. The argument against legumes is never explicitly stated, except for his statement that they contain lectins that aggravate autoimmune diseases. There does not appear to be a scientific consensus on this point at this time. Some research implicates lectins in some autoimmune diseases, but there is no clear evidence for the method by which this may occur. Also legumes contain protease inhibitors that have anti-inflammatory properties after cooking. Furthermore there is evidence of Paleolithic peoples consuming legumes and processing grains long before they began growing them.

Grains, legumes and dairy can all be excellent sources of nutrition. The agricultural revolution that occurred approximately 10,000 ya in multiple locations around the world dramatically changed human history. Humans were no longer nomadic hunter-gatherers. As agriculture spread some populations settled in location permanently and their population size exploded.

The process of domestication of plant and animal species was not as fast as Dr. Cordain implies. In order to domesticate a plant or animal species it’s entire life cycle, and especially it’s reproductive cycle needs to be well understood. The process of domestication takes generations. Not every attempt at domestication was successful either. In order to domesticate a plant or animal species it had to be very familiar and useful to the population, which means they had to eat or use it regularly. The species of fruits and vegetables available today have changed dramatically from the species that would have been available in the Paleolithic due to selective breeding for thousands of years.

The argument against dairy is one of the more illogical arguments in the Paleo Diet. Dr. Cordain once again commits the appeal to nature fallacy and argues that we have not had enough time to evolve to eat dairy. This is patently untrue for individuals who are lactose tolerant. Lactose intolerance is indeed the” natural” human state, however approximately 7,500 ya in Europe a single allele mutation allowing for lactase persistence emerged. This adaptation allowed adults to digest lactose, a sugar found in milk. Due to positive evolutionary pressure these genes became fixed in the populations very quickly. Today the rates of lactase persistence vary in Europe from as low as 15-54% of the population in eastern and southern Europe, to 62-86% in central and western Europe, to a high of 89-96% in the British Isles and Scandinavia. While lactase persistence has been most intensively studied in Europe, it is also found in other populations around the world including populations in Africa and India. Lactase persistence is found societies that were historically pastoral, that is they herded cattle. Perhaps more interesting is that there are multiple derived alleles allowing for lactase persistence that evolved independently.

One further claim Dr. Cordain makes regarding dairy is the body does properly not absorb the calcium in diary products and that eating too much dairy can increase osteoporosis risk. This has been hypothesized but further studies have found no evidence to support this conclusion. Dr. Cordain makes this claim as part of his discussion of the need to keep the diet more alkaline than acidic. This brings in elements of the alkaline dietary trends, which are also unsubstantiated by current research available. Furthermore idea of balancing acidic and alkaline foods suggested by Dr. Cordain is not actually upheld in studies of hunter-gatherer societies.

The Paleo Diet makes repeated claims that eating the way Dr. Cordain believes our ancestors did will cure diseases that he believes are caused by eating “unnatural” foods such as grains, legumes and dairy. These claims are not supported by the archaeological record, which shows no single Paleolithic diet or dietary pattern, and as previously discussed is not supported by the study of ancient remains. Specifically Dr. Cordain believes that heart disease, autoimmune diseases and even skin cancer can be prevented by eating his diet despite there being no evidence to support this. The book also relies heavily on anecdotes provided by people who claim the diet has cured them along with a brief explanation about how this allegedly works that does not actually provide any scientific information in the second half of the book. Any time personal anecdotes are being provided instead of scientific evidence it should be a red flag to begin to look more deeply into the claims.

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