Last week I tuned into BBC2 for Giles Coren's magnificent documentary Eat to Live Forever. The documentary focused on a number of different diets whose proponents all claim will help to significantly extend your lifespan. These included calorie restriction, fruitarianism and most interestingly of all, the paleo diet. I say interestingly because of all the diets mentioned, paleo was the one I had heard about before. However, like most fad diets and other nutritional pseudoscience I hadn't looked at in great detail. I had just assumed that the paleo diet was another crackpot idea to be tossed on the mountain of such ideas in the world of CAM. Since the programme aired though I have been doing a fair bit of research into the paleo diet and I have to admit I wasn't prepared for what I found. The paleo diet theory isn't just wrong. It's fractally wrong. The wrongness of each component claim is self-similar with the overall wrongness of the theory. It is, in the words of Linus Pauling, not even wrong. It is so profoundly flawed in such a childlike way that I was surprised, shocked even, at how popular it is. There are all sorts of food outlets from fast food and street food to fine dining which cater for paleo diets. How does such an obviously ludicrous idea gain so much traction? Well here's how.
Firstly, let's have a look, in detail, at the reasons why the Paleo diet is so badly flawed.
The Paleo diet for those who are unfamiliar, is a lifestyle diet which advocates a diet low in carbohydrates, high in animal based protein and fat and free from dairy, processed foods, grains, legumes and basically any food less than 10,000 years old. The reason for this, proponents claim, is that our modern anatomy and genetics which responds so poorly to our modern diet is adapted only to eat foods that our ancestors would have eaten in the paleolithic era (i.e. ~2.6 mya - 10kya). Switching to this "caveman" diet will help you to live longer and be healthier. Yeah, right!
OK, so let's outline the critical flaws in the paleo diet.
1. On the Paleolithic Era
The first fly in the ointment is the concept of the paleolithic era as being the formative era in which our biology was adapted.
The paleolithic era covers a period between 2.5 million years ago and 10,000 years ago. This creates two problems. Firstly, the reason why the paleolithic era is bookended by these two dates is because 2.5 million years ago is the era to which the earliest discovered tools date and 10,000 years ago represents the advent of modern agriculture. This means that the paleolithic era is a period defined by archaeology and not biology.
As it happens, the date for the beginning of the paleolithic era is now out of date. While the date range for the paleolithic era remains fixed, we now know that human tool usage dates back at least 3.4 million years
As it happens, the date for the beginning of the paleolithic era is now out of date. While the date range for the paleolithic era remains fixed, we now know that human tool usage dates back at least 3.4 million years
Evidence for stone-tool-assisted consumption of animal tissues before 3.39 million years ago at Dikika, Ethiopia
Which leads us on to our second problem.
The idea that our diet was shaped in the paleolithic era is clearly ridiculous to anyone who is familiar with human evolution. 2.5 million years ago our ancestors looked something like this:
This is a reconstruction of Australopithecus Afarensis. 2.5 million years ago was a in the midst of the period when the genus Homo arose from A. Afarensis.
Of course, the lines between the emergence of Homo from Australopithecus aren't exactly clearly defined and there remains some debate in the literature as to whether H. Habilis, the first species to emerge from the Homo genus should actually be classed as Homo or Australopithecus.
In any case, we went from Australopithecus above through to Homo Habilis:
Of course, the lines between the emergence of Homo from Australopithecus aren't exactly clearly defined and there remains some debate in the literature as to whether H. Habilis, the first species to emerge from the Homo genus should actually be classed as Homo or Australopithecus.
In any case, we went from Australopithecus above through to Homo Habilis:
and Homo Erectus
and Homo Heidelbergensis
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and finally Homo Sapiens.
As we can see from the forensic reconstructions above, the genus Homo changed massively during the Palaeolithic era and the idea that our diet was settled on during this period is ludicrous. There are a number of reasons for this.
Firstly, our genome is significant to a considerable amount of change every generation. Our current best estimate for the base mutation rate is 128. This means that, on average, each of us is born with 128 changes from our parents genomes.
Mutation rates in humans. II. Sporadic mutation-specific rates and rate of detrimental human mutations inferred from hemophilia B.
Secondly, there is the fact that we still have very little understanding of certain aspects of our own evolution. There are still topics which are hotly debated such as whether humans evolved simultaneously in different regions or whether we spread out from Africa.
Recent African origin of modern humans
Multiregional origin of modern humans
There are still gaps in our knowledge regarding key factors in the origin of modern humans. As a result, any claim such as that made by paleo diet advocates which suggests definite knowledge where none can possibly exist is wrong.
Firstly, our genome is significant to a considerable amount of change every generation. Our current best estimate for the base mutation rate is 128. This means that, on average, each of us is born with 128 changes from our parents genomes.
Mutation rates in humans. II. Sporadic mutation-specific rates and rate of detrimental human mutations inferred from hemophilia B.
Secondly, there is the fact that we still have very little understanding of certain aspects of our own evolution. There are still topics which are hotly debated such as whether humans evolved simultaneously in different regions or whether we spread out from Africa.
Recent African origin of modern humans
Multiregional origin of modern humans
There are still gaps in our knowledge regarding key factors in the origin of modern humans. As a result, any claim such as that made by paleo diet advocates which suggests definite knowledge where none can possibly exist is wrong.
2. On the speed of human evolution.
Quite possibly the most glaring error in the paleo diet hypothesis is the failure to recognise the actual capability of humans to adapt to their environment. It is suggested by Paleo advocates that our diet should exclude things like dairy because these things were not in our diet 10,000 years ago. Yes, its true that dairy farming is an activity which humans have been practising for less than 10,000 years. But its also demonstrably false to claim that humans haven't adapted to it. One of the most clearcut examples of this is the evolution of lactose tolerance. Since I'm Irish and Irish people are one of the ethnic groups predisposed towards lactose tolerance I've always been quite interested in the science of lactose tolerance.
The ancestral state of humans (i.e. the default genetic condition of humans prior to 10,000 years ago) was one of lactase non-persistence. What this means is that at birth a gene on chromosome 2 gets switched on which causes the body to produce an enzyme, lactase, which gives babies the ability to digest a particular sugar, lactose, present in milk. However, as the child gets older (between 18 months and 2 years) weaning becomes more likely and the production of lactase in the body gradually diminishes. Eventually it stops altogether resulting in lactose intolerance. There are, however, a number of ethnic groups which do not suffer from this affliction: the Irish, Czech and Spanish as well as a number of tribal peoples such as the Tutsi of central Africa, the Fulani of western Africa and the Bedouin, Tuareg and Beja nomadic peoples. This is quite a diverse bunch but the one thing they all have in common is a long history of dairy farming.
The resulting fruit had the large size of the Chilean strawberry combined with the sweetness of the Virginia strawberry.
Almost all foods we eat today bear no resemblance to those which our ancestors would have eaten prior to 10,000 years ago. Since the dawn of farming we have modified all the foods we eat to be more pleasant to eat, higher yield, more flavour etc. So the idea that restricting yourself to any subset of our modern diet resembles a paleolithic diet is ridiculous.
4. On Paleolithic health outcomes
The final damning flaw in the paleo diet logic is the idea that we should return to the diet of our ancestors so that our health will be better and our lifespan extended. The question is though, what was the health of our ancestors like and how long did they live?
Well, as it turns out, the answer is that our ancestors lived short lives with high infant and adult mortality rates. Many children died before they reached the age of 15 and those who reached adulthood could only expect to live until their early forties.
High adult mortality among Hiwi hunter-gatherers: Implications for human evolution
Older age becomes common late in human evolution
OK, so we didn't live that long in the Paleolithic era but surely those short lives must have been full of health, free from modern processed foods. Again, no. Even in this respect the paleo diet is wrong. Just to take one example, the disease atherosclerosis (the arteries being clogged with fatty deposits) is generally considered to be a modern lifestyle-based disease which our ancestors did not suffer from. Indeed, in "The Paleo Prescription" Boyd Eaton uses the absence of atherosclerosis in modern hunter-gatherer societies to buttress his argument. The reality is, as usual, different. It turns out that in a study of ancient populations, atherosclerosis was quite prevalent, with evidence of this disease at least as far back as 4000 years ago.
Atherosclerosis across 4000 years of human history: the Horus study of four ancient populations.
5. On sloppy research
The final section of this post concerns the research upon which the bible of Paleo dieters, "The Paleo Prescription" by S. Boyd Eaton is based. While this doesn't (in and of itself) condemn the underlying logic of the Paleo diet, it does undermine the conclusions reached by Cordain in his book.
The core problem is the paucity of research on modern hunter-gatherer societies which is presented as the bedrock of the diet's premise. The book studies modern hunter-gatherer societies so as to examine how their diet fits into their health outcomes. However, only six social groups were included in the book: the !Kung, Inuit, Mbuti, Agta, Hadza and Australian aboriginal peoples. This lack of research further creates problems of its own.
Firstly, the conclusions based on the above data are already suspect. The data on the Kung was the result of just one month's record of their diet. The diet of the Eskimos is already highly restrictive through environment, rather than choice. Even if no other groups were looked at, the conclusions based on the six groups studied should have come with a strongly worded caveat.
Secondly, the book fails to account for the actual variety in modern hunter-gatherer societies:
(Image credit: Jen Christiansen/Sci-Am)
Given the wide variations in actual dietary patterns among modern hunter-gatherer societies, drawing conclusions about the health benefits of a diet based on a cherry-picked view of them is unfounded and downright irresponsible, scientifically at least.
Finally, the book also fails to account for contrary evidence. In particular the Hiwi people of Venezuela which I have referenced in the section on health outcomes above. The fact that there are modern hunter-gatherer societies which have poor health outcomes, in part as a consequence of their diet serves to further undermine Eaton's conclusions.
Conclusions
The Paleo diet is attractive to a lot of people for a number of reasons. Firstly, it offers the prospect of better health outcomes and longer lives, something which traditional diets (i.e. those focused on weight loss alone) don't. Secondly, it offers a semblance of being scientifically grounded (the evolutionary discordance hypothesis) and rooted in common sense (cutting out processed foods). Finally, it offers something that a lot of conspiracy theories also offer, a patchwork theory crafted from disparate and often demonstrably false ideas which those who advocate it seem to think has gone unnoticed by the general population.
The Paleo diet does contain some good ideas such as reducing your intake of processed foods and carbohydrates (particularly if like most people you lead a less active life) and increasing your intake of fresh food. However, the Paleo diet as a whole is best done with caution. It can and does lead to weight loss but then so do a lot of diets. However, by restricting or eliminating certain food groups (e.g. dairy) the diet can lead to nutrient deficiencies. On the whole it's best to be avoided.
The ancestral state of humans (i.e. the default genetic condition of humans prior to 10,000 years ago) was one of lactase non-persistence. What this means is that at birth a gene on chromosome 2 gets switched on which causes the body to produce an enzyme, lactase, which gives babies the ability to digest a particular sugar, lactose, present in milk. However, as the child gets older (between 18 months and 2 years) weaning becomes more likely and the production of lactase in the body gradually diminishes. Eventually it stops altogether resulting in lactose intolerance. There are, however, a number of ethnic groups which do not suffer from this affliction: the Irish, Czech and Spanish as well as a number of tribal peoples such as the Tutsi of central Africa, the Fulani of western Africa and the Bedouin, Tuareg and Beja nomadic peoples. This is quite a diverse bunch but the one thing they all have in common is a long history of dairy farming.
Evolutionary Genetics: Genetics of lactase persistence – fresh lessons in the history of milk drinking
3. On Artificial Selection
One of the things that escapes most people is just how much we have changed the food we eat by growing it. The Paleo diet ignores this fact and crumbles as a result.
Let's take the banana as an example. If we compare the banana that everyone is used to buying in the supermarket vs. the wild banana as it would have existed 10,000 years ago we can see the difference:
The wild banana on the right is what bananas looked like before the advent of domestication c. 8000 BCE. It is filled with seeds and is inedible.
Another example of this phenomenon is the common garden strawberry. Prior to the mid 1700s the strawberry that most Europeans were familiar with was the Virigina strawberry:
Then in the 1750s, the Virginia strawberry was crossed with the recently introduced Chilean white strawberry:Let's take the banana as an example. If we compare the banana that everyone is used to buying in the supermarket vs. the wild banana as it would have existed 10,000 years ago we can see the difference:
The wild banana on the right is what bananas looked like before the advent of domestication c. 8000 BCE. It is filled with seeds and is inedible.
Another example of this phenomenon is the common garden strawberry. Prior to the mid 1700s the strawberry that most Europeans were familiar with was the Virigina strawberry:
The resulting fruit had the large size of the Chilean strawberry combined with the sweetness of the Virginia strawberry.
Almost all foods we eat today bear no resemblance to those which our ancestors would have eaten prior to 10,000 years ago. Since the dawn of farming we have modified all the foods we eat to be more pleasant to eat, higher yield, more flavour etc. So the idea that restricting yourself to any subset of our modern diet resembles a paleolithic diet is ridiculous.
4. On Paleolithic health outcomes
The final damning flaw in the paleo diet logic is the idea that we should return to the diet of our ancestors so that our health will be better and our lifespan extended. The question is though, what was the health of our ancestors like and how long did they live?
Well, as it turns out, the answer is that our ancestors lived short lives with high infant and adult mortality rates. Many children died before they reached the age of 15 and those who reached adulthood could only expect to live until their early forties.
High adult mortality among Hiwi hunter-gatherers: Implications for human evolution
Older age becomes common late in human evolution
OK, so we didn't live that long in the Paleolithic era but surely those short lives must have been full of health, free from modern processed foods. Again, no. Even in this respect the paleo diet is wrong. Just to take one example, the disease atherosclerosis (the arteries being clogged with fatty deposits) is generally considered to be a modern lifestyle-based disease which our ancestors did not suffer from. Indeed, in "The Paleo Prescription" Boyd Eaton uses the absence of atherosclerosis in modern hunter-gatherer societies to buttress his argument. The reality is, as usual, different. It turns out that in a study of ancient populations, atherosclerosis was quite prevalent, with evidence of this disease at least as far back as 4000 years ago.
Atherosclerosis across 4000 years of human history: the Horus study of four ancient populations.
5. On sloppy research
The final section of this post concerns the research upon which the bible of Paleo dieters, "The Paleo Prescription" by S. Boyd Eaton is based. While this doesn't (in and of itself) condemn the underlying logic of the Paleo diet, it does undermine the conclusions reached by Cordain in his book.
The core problem is the paucity of research on modern hunter-gatherer societies which is presented as the bedrock of the diet's premise. The book studies modern hunter-gatherer societies so as to examine how their diet fits into their health outcomes. However, only six social groups were included in the book: the !Kung, Inuit, Mbuti, Agta, Hadza and Australian aboriginal peoples. This lack of research further creates problems of its own.
Firstly, the conclusions based on the above data are already suspect. The data on the Kung was the result of just one month's record of their diet. The diet of the Eskimos is already highly restrictive through environment, rather than choice. Even if no other groups were looked at, the conclusions based on the six groups studied should have come with a strongly worded caveat.
Secondly, the book fails to account for the actual variety in modern hunter-gatherer societies:
Given the wide variations in actual dietary patterns among modern hunter-gatherer societies, drawing conclusions about the health benefits of a diet based on a cherry-picked view of them is unfounded and downright irresponsible, scientifically at least.
Finally, the book also fails to account for contrary evidence. In particular the Hiwi people of Venezuela which I have referenced in the section on health outcomes above. The fact that there are modern hunter-gatherer societies which have poor health outcomes, in part as a consequence of their diet serves to further undermine Eaton's conclusions.
Conclusions
The Paleo diet is attractive to a lot of people for a number of reasons. Firstly, it offers the prospect of better health outcomes and longer lives, something which traditional diets (i.e. those focused on weight loss alone) don't. Secondly, it offers a semblance of being scientifically grounded (the evolutionary discordance hypothesis) and rooted in common sense (cutting out processed foods). Finally, it offers something that a lot of conspiracy theories also offer, a patchwork theory crafted from disparate and often demonstrably false ideas which those who advocate it seem to think has gone unnoticed by the general population.
The Paleo diet does contain some good ideas such as reducing your intake of processed foods and carbohydrates (particularly if like most people you lead a less active life) and increasing your intake of fresh food. However, the Paleo diet as a whole is best done with caution. It can and does lead to weight loss but then so do a lot of diets. However, by restricting or eliminating certain food groups (e.g. dairy) the diet can lead to nutrient deficiencies. On the whole it's best to be avoided.
