Justine Butler, Senior Health Researcher at Viva!, examines the claims for the Paleo diet…
Some time ago I watched a programme about the different types of diets people follow. There was a banker who saw himself as a modern day hunter-gatherer in the city. He explained how he followed a Paleo diet, while some fatty slices of bacon sizzled away in a saucepan behind him.
But would he be willing or able to snatch up a rabbit and tear at the raw flesh with his nails and teeth? This is what true carnivores do. The idea that we are ‘designed’ to eat meat is fundamentally flawed on many levels and the theory behind the Paleo diet is wrong.
We’ve all heard the saying “we are designed to eat meat”. Someone even said to me “that’s what my canines are for!” – they were seriously comparing their little teeth with a lion’s giant canines that can reach up to a deadly seven centimetres in length!
Herbivore, carnivore or omnivore?
We are very different to carnivores such as cats, dogs and wolves. They have strong jaws that can only open and shut. Their teeth and claws are sharp in order to tear off chunks of raw meat and ‘wolf’ them down. Their acidic stomachs help them to quickly digest flesh and their short intestines allow the rapid expulsion of rotting meat remains. On the other hand, herbivores, such as rabbits, horses and sheep, chew from side-to-side, their saliva contains digestive enzymes and they have longer intestines to absorb nutrients.
When asked if humans are herbivores, carnivores, or omnivores, Dr William C. Roberts, Editor-in-Chief, of The American Journal of Cardiology said: “Although most of us conduct our lives as omnivores, in that we eat flesh as well as vegetables and fruits, human beings have characteristics of herbivores, not carnivores”.
Researchers from Harvard University say that during human evolution, meat may have contributed to dietary quality but meat-eating alone could not have supported the evolution of human traits, because modern humans fare poorly on diets that include raw meat. Some say it was cooking food that substantially improved the quality of people’s diet. Meat-eating may well have made cooking necessary as raw meat is difficult to chew and takes time to digest, making the consumption in large quantities extremely difficult.
In the 1980s, US anthropologists Boyd Eaton and Melvin Konner suggested the Paleo (Paleolithic or hunter-gatherer) diet as a model for modern human nutrition. Consisting of high-protein meat and fish (but no dairy), it contains no fibre, grains or pulses in it.
The theory has been widely incorporated into popular scientific and diet research, leading to the idea that human bodies haven’t changed since the Paleolithic period of 2.6 million to 12,000 years ago. Proponents reckon the mismatch between the diets then and our Western-style diets now, is to blame for our high levels of obesity, diabetes and heart disease.
We’ve certainly evolved to be flexible eaters and genetic evidence shows that we continued to evolve over the past 40,000 years, past the Paleolithic era well into the Neolithic era when farming began. During the Neolithic period, farming rapidly spread across Europe, reaching Britain and Northern Europe around 6,000 years ago. These Neolithic farmers relied on a mostly plant-based diet compared to the Paleolithic hunter-gatherers that preceded them. In fact, geochemical analysis of grains and pulses coming from Neolithic sites confirms that the early farmers of 10,000 years ago relied much more heavily on plant protein than was previously thought.
Evidence shows that genetic changes occurred relatively recently and these helped us adapt to a more plant-based diet. One modern adaptation included an increased production of amylase, an enzyme that helps us digest starchy carbohydrates found in cereals and grains.
A study, published in the journal Nature Ecology and Evolution, shows how the shift in European diets after the introduction of farming led to other genetic adaptations that favoured the predominantly plant-based diet of that time. Long-chain fatty acids are important for brain development and cognitive function. Neolithic farmers probably ate less of these than their predecessors and evidence shows that we developed enzymes to make these long chain fats in the body from short chain ones found widely in plant foods such as nuts and seeds. The evidence shows that we have adapted and changed and are not the same as our Paleolithic ancestors.
Meat not make man smart
Another myth surrounding meat consumption is the idea that ‘meat made us smart’. In the 1990s, British scientists Leslie C. Aiello and Peter Wheeler proposed the ‘expensive-tissue hypothesis’, whereby there is a trade-off between the size of the digestive tract (gut) and the brain – small gut allows big brain. If bigger brains were always better, every animal would have them, so there must be a downside.
The brain is ‘expensive’ because it requires so much energy. The theory is that a high-quality diet enabled us to reduce the size of our gut, freeing up energy to increase brain size. In other words ‘meat made us smart’. However, recent research, published in the journal Nature, refutes this, saying a higher quality diet coupled with the energy saved by walking upright, growing more slowly and reproducing later, fuelled the growth in brain size. Prehistoric humans ate some meat, but it certainly didn’t make them smart.
The science shows that humans have more characteristics in common with herbivores than they do carnivores. We are not suited to eating raw meat and cooked meat, even at moderate levels, is associated with a wide range of health problems, including heart disease, diabetes and cancer – all the modern diseases Paleo pundits suggest meaty diets can protect against.
The idea that we are suited to a hunter-gatherer diet, rich in meat and fish with no grains or pulses, is flawed. We know humans continued evolving past the Palaeolithic era; we know our Neolithic ancestors adapted to be able to digest carbohydrates; and we now know that they relied on plant protein more than previously thought. The research simply doesn’t support the notion that humans were designed to eat meat, especially in the quantities consumed in some affluent countries.
To find out more, see Viva!’s Wheat Eaters or Meat Eaters? guide with anatomy charts of carnivores, herbivores, omnivores and humans, which looks at our dietary history and explains why we consume animals at our peril.