The Paleo diet is based on the idea that the agricultural revolution (roughly ten thousand years ago), and a switch to grain based agriculture, dramatically changed the way humans ate, and as a species our genes have not had time to properly adapt. This, advocates say, is the route cause of many modern health problems – we are stuck with Paleolithic genes in an agricultural world.
Followers of the diet suggest that we should return to eating in a way that is more in line with our genetics, restricting ourselves to foods that more closely resemble that of our ancient ancestors. So grains, potatoes and dairy products are avoided, as these are foods that were only common after the agricultural revolution. Meats, vegetables, fruits and nuts are eaten in abundance, reflecting the hunter gatherer lifestyle of humans in the middle Paleolithic.
Nourishment Network spoke to the geneticist Giles Yeo about the Paleo Diet, and the sometimes surprising role that the food we eat has on our genes – and even on the genetics of other species.
What are the main ways in which a shift to agriculture changed our diet?
It is impossible to overstate the role that the agricultural revolution played in the development of human civilisation, for better or worse, as it exists today. Agriculture meant far higher food yields and thus the ability to support higher population densities.
The main problem with agriculture however, is that it has resulted in a stunning reduction in the diversity of foods that we as humans eat, and consequently a huge shift in the sources from where we obtain our calories. Our continued reliance on the starch rich seeds from five different grasses as our main source of calories is a perfect case in point.
Today, the starch rich seeds of five grasses (wheat, rice, oats, corn and barley) provide 50% of the calories consumed by all humans. This is very different to what our stone-age hunter gatherer ancestors would have faced. The issue is not with the sources of protein or vegetables, which although less varied, are what would have been hunted or gathered in the past, or even with starch per se, which would have been present in the grasses or roots that were gathered. The problem is with the amount of starch that was suddenly available. Our foraging ancestor in the Pleistocene may have occasionally happened upon a field of early wheat or rice, but his caloric base would have come from a huge variety of foods, nuts, berries and game.
A second issue is the appearance of entirely new sources of food that were only possible after the establishment of agriculture. Consumption of milk, for example, would only have made sense once herd animals had been domesticated. And likewise the fermentation of fruit and grain to produce alcoholic beverages would only have been possible if there was an excess of such foods.
And the truth of the matter is that the transition from hunter-gatherer to farmer was not smooth at all. We know this from the archaeological evidence. Early farmers suffered from severe malnutrition and disease. Yet, the advantages of agriculture to the growth and proliferation of our species were just too great, and so humans, flexible as we are, eventually adapted to agriculture.
How exactly did we adapt to these changes?
We found ways to improve our efficiency of extracting the calories densely locked up in starch and even to rapidly remove alcohol from our blood-stream so as not to poison ourselves (too much). Some populations also adapted to enable them to digest lactose into adulthood, allowing the consumption of dairy from domesticated animals.
In humans, our ability to digest starch begins with amylase in saliva, which helps break down starch during chewing, and continues its action as it travels down to the stomach, and through to the small intestine, where other amylases released from the pancreas and other organs take over. Although we typically carry two copies of any given gene, one from each parent, humans actually have a variable number of the saliva amylase gene AMY1, ranging from 2 to more than 30 copies. The more copies of AMY1, the better our ability to digest starch. Genetic studies on existing hunter-gatherer peoples today, such as the Yanomami people of Venezuela, who continue to subsist on a high protein and low starch diet, reveal they have fewer copies of AMY1; while other primates, who are primarily fruit eaters only ever have 2 copies of AMY1.
Humans have always eaten starch, we just were not able to fully digest it and unlock all of the available calories. This was not a problem when starch was not our overwhelming source of calories (such as for the Yanomami), which it is, of course, today. What this genetic adaptation has done is to improve our efficiency to metabolise starch, allowing us to extract more calories from every gram. Or to look at it another way, we could eat less food and get the same number of calories, providing a huge selective advantage over those without the genetic adaptation.
So even though it was only ten thousand years ago, the switch to agriculture has affected our genes. Did it have any other effects?
Our shift to a starch-rich diet had one other unintended consequence that ended up significantly influencing human culture; it was a major driving factor in the domestication of dogs. Dogs were domesticated from wolves at around the same time as the emergence of agriculture. Dogs don’t have salivary amylase, but have an amylase that is produced by the pancreas called AMY2B. Similar to AMY1 in humans, dogs have a variable number of AMY2B genes, with more copies indicating a better ability digest starch. Wolves however, only appear to have 2 copies of AMY2B. Together with a less vicious disposition, the enhanced ability of the ancestors of modern dogs to digest starch led to them being able to subsist off human starch-rich food waste, a valuable source of energy, and they were therefore less likely to eat their human companions (that would not have worked out). People often assume that dogs are ‘obligate’ carnivores, a fact which is true for wolves and indeed cats. However, a peek at the ingredient list of any brand of packaged dog-food will reveal a surprisingly high starch content!
The early communities that were able to domesticate dogs had a large selection advantage over other non-dog owning communities, arising from an enhanced ability to defend their villages and herds, and also an improved ability to hunt, which provided a useful dietary supplement to the domesticated herds. Thus humans and dogs had a convergent evolution in their ability to digest starch, which was driven by the advantages afforded by our symbiotic relationship; dogs got a predictable supply of food, while humans obtained protection and companionship. And of course this oldest of relationships between humans and dogs continues to today, and we have the humblest of food, starch, to thank for it.
In terms of the Paleo diet, do you think that there is anything to be said for it?
There are aspects of Paleo that are okay. For example the higher protein intake, while of course keeping it in balance with the increased risk of cancers that come with too much red or processed meat.
But others are complete BS. Saying that grains, legumes or potatoes need to be avoided at all cost, because we NEVER saw these pre-agriculture. Of course we saw them! Just not to the amounts we see now. The paleo-bots are simply pasting an ‘idealized’ flintstone world of 100,000 years gone by, and as with many fad diets, they make wild and exuberant claims about health and weight loss.
Giles Yeo is a geneticist with nearly 20 years’ experience studying obesity and the brain control of food intake. He obtained his PhD from the University of Cambridge in genetics in 1998 and has been there ever since. He is also known for his television work, including presenting BBC Horizon’s ‘Why are we getting so fat?’ and ‘Clean eating – The dirty truth’.