May 24, 2024

The paleo diet is a ‘Flintstone fantasy’. A scientist explains why

Most non-communicable diseases are diet-related, including obesity and its associated illnesses. Because the prevalence in obesity is a contemporary problem, some argue that our modern diet, based on agriculture, is to blame. This is the so-called ‘paleo’ movement.

‘Paleo’ is a contraction of Palaeolithic, the period from about 2.6 million years ago to 10,000BC (the Stone Age). The paleo premise is that for most of human existence, we were hunter-gatherers.

Then the agricultural revolution changed our diet and our current problems with diet-related illnesses occur because we haven’t yet adapted to it. Hence the suggested solution of to return to a ‘paleo diet’.

There are two main problems with this argument. First, there is no single paleo diet, because there was no singular Palaeolithic people – hunter-gatherers ate whatever was available to them.

Second, the contention that humans haven’t had time to adapt to an agricultural diet is simply incorrect, because when the right selection pressure is present, humans can adapt (and have) in just a few thousand years. Three examples of such adaptations are our ability to consume large amounts of starch, milk and alcohol.

Digestion of starch begins with amylase in saliva, which breaks down starch as we chew, and as the food moves to the stomach and small intestine, where other amylases from the pancreas and other organs take over.

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Although we typically carry two copies of most genes, one from each parent, humans have a variable number of the amylase-encoding gene AMY1, ranging from two to more than 30. The more AMY1, the better your ability to digest starch.

Genetic studies on hunter-gatherer peoples today, who subsist on high-protein/low-starch diets, reveal they have fewer copies of AMY1; while other primates, who mainly eat fruit, only ever have two.

Humans have always eaten starch, we were just unable to access all of the available calories. This wasn’t a problem when starch wasn’t our main source of calories, which it is today. This genetic adaptation improved our efficiency to metabolise starch, meaning we could eat less food and get the same number of calories.

This increased nutritional efficiency provided a huge selective advantage, and was thus incorporated into gene-pool. As such, almost all humans today carry multiple copies of AMY1.

Then there’s milk. All humans can drink milk in early life, but many then switch to being lactose intolerant as they begin adulthood. However, with the domestication of large ruminants, people began to realise that compared to simply eating the animals, drinking their milk greatly increased the calories available from each animal during its life.

Couple this with the development of cheese, which allowed for the nutrients in milk to be preserved in compact and portable form and voilà: a new, rich and renewable food source was available to nascent herding communities.

So powerful was the selection pressure in herding societies that the ability to digest lactose as adults actually emerged independently at least three times: in northern Europe and in two geographically distinct African populations.

The incredible thing is that although the adaptation in the three cases involved different genetic changes, they all influence the same gene, lactase, required for metabolising lactose into glucose. But lactose is lactose, no matter which type of milk it’s found in.

So, if you have the genetic adaptation to digest lactose as an adult, then milk, whether from human, cow, sheep or goat, isn’t going to be bad for you.

Finally, the consumption of alcohol coincided with the emergence of agriculture, when humans began turning fermented fruit and other foods into alcoholic drinks. This influenced the way certain populations solved the problem of safe drinking water.

Beer and wine, were used by those in the Fertile Crescent (today’s Middle East) and northern Europe to ensure safe drinking water. In fact, European children drank weak beer up until the 17th century. Thus an enhanced ability to metabolise alcohol was a powerful selective advantage.

Other cultures, like East Asians, relied on boiling water instead. To be clear, ancient East Asians did drink alcohol (residue of the earliest known alcoholic beverage was found in a Neolithic Chinese village dating to 7,000-6,600BC).

But because East Asians had clean boiled water, they didn’t have to drink alcohol, unlike Northern Europeans. Thus emerged the variation in the ability of different populations today to handle alcohol.

Ultimately, the paleo movement is a ‘Flintstone’ fantasy. The reality is that humans are like cockroaches, adapting when we have to, particularly to the selection pressure of changing nutritional demands post agriculture.

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