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Charmian Smith talks to anthropologist and emeritus professor Helen Leach about myth, misconceptions and the paleolithic diet.
The paleo diet is sometimes called the Stone Age diet, but the palaeolithic is not necessarily the same as the Stone Age, University of Otago emeritus professor Helen Leach explains.
''Palaeolithic'' refers to the stage when our hominin ancestors and later humans made chipped stone tools in the Pleistocene epoch from about two and a-half million years ago till the end of the ice ages about 10,000 years ago.
Then came the Neolithic, the new Stone Age, when humans made polished stone tools and developed agriculture as the climate warmed and the ice retreated. This was later followed by the so-called Bronze and Iron Ages when humans developed metal technologies.
The palaeolithic stage prevailed for very long time and includes not only the cultures of our species, Homo sapiens, but also those of earlier hominins such as Homo erectus and Neanderthals.
There were obviously many varied diets among early humans and hominins depending on their environment, the climate, what resources were available and the level of their technology, Prof Leach says.
If you are going to recommend a palaeolithic diet, then which one do you choose and how do you discover what they ate? she asks.
The Paleo Diet is actually the trademark of a company founded in 2006 by American academic Loren Cordain and others. Cordain had previously worked in health science and exercise but on his website, www.thepaleodiet.com, he is described as ''the world's leading expert on Paleolithic diets and founder of the Paleolithic movement''.
He sells popular books and food products.
Much of his work was based on that of Boyd Eaton and Melvin Konner whose paper on paleolithic nutrition was published in 1985. They were building on the work of people before them, so the idea goes back a long way, Prof Leach said.
Cordain and Eaton collaborated on several research projects over the years, but Cordain wrote many popular books on the subject.
More recently the paleo diet has been promoted by Australian chef Pete Evans, who has written several popular cookbooks on the topic, although in his latest book, Easy Keto, he has moved on to another diet.
Advocates of such diets claim that humans evolved to eat as our hunter-gatherer ancestors did and that subsequent cultural changes associated with agriculture have gone too fast for our genes to catch up.
They argue this mismatch between biology and lifestyle fosters diseases of civilisation, now referred to as diseases of affluence, such as high blood pressure, heart attacks, strokes, cancer, diabetes, obesity, emphysema, hypertension, cirrhosis, osteoporosis, hearing loss, dental caries, diverticular disease, obesity - and even acne.
The idea was that if we returned to the diet our ancestors ate, we would avoid those diseases.
The paleo diet generally recommends eating grass-fed meat, fish, fresh vegetables and fruit and some nuts and seeds, and avoiding foods it claims were introduced after the advent of agriculture some 10,000 years ago, such as grains, legumes, dairy and potatoes. It also proscribes refined sugars and processed foods.
''The genomes of all species on planet Earth were selected in past environments that were different from the present day because of the instability of this planet's climate,'' Prof Leach says.
However, evolutionary selection has not ceased in the past 10,000 years, and she points to the selection for a gene that enabled adults to tolerate lactose in milk that developed widely in groups in Europe and the Middle East who domesticated cattle and goats, but not in other populations.
It is difficult to discover what was actually eaten in paleolithic times and the proportions of various foods as archaeological evidence, such as bones, tend to favour recognition of meat.
Advocates of the paleolithic diet resorted to looking at 20th-century hunter-gatherer groups using material collected by American anthropologist G.P. Murdock, who had used writings from not only ethnographers but also explorers and missionaries so varied in reliability.
The 58 groups described had been marginalised into difficult environments, none still made stone tools and indeed many used iron cooking pots. Women's contributions to food gathering were often unreported by male ethnographers and very few records provided quantities of food or the time spent obtaining it, Prof Leach said.
As might be expected, a variety of diets was found, from Inuit in Arctic regions who ate mainly large mammals, to those in warmer climates who had access to, and ate more plant foods. The averaged balance for all hunter-gatherers was 65% plant food and 35% animal food, although Cordain later advocated a ''strong'', more meat-based diet.
The only common factor was their omnivory, Prof Leach said.
''All of us living in the so-called civilised world were to be treated as genetically adapted to this diet, despite the fact that our common ancestors with these extant hunter-gatherer communities might be as far back as 40,000 or even as long as 160,000 years ago.''
However, in the past 20 or 30 years archaeological excavations and new techniques for analysis of tiny plant particles have revealed evidence of the real paleolithic diet of some 20,000 to 30,000 years ago in the Mediterranean area, when northern parts of Europe were still covered in ice.
The first of these sites to be studied, Ohalo II on the Sea of Galilee in Israel, revealed numerous wild cereal grains found in association with brushwood huts and hearths. The first study on it was published in 1992, so the material would have been available to Cordain at the time he founded his company, although he did not refer to it.
''Many subsequent articles have filled out the picture of a community who about 23,000 years ago fished, hunted gazelles, fallow deer, hares, foxes, wild cattle and boars, caught 80 species of birds, most of them water fowl. They gathered fruit and nuts including wild almond, hawthorn, pistachio nuts, acorns, olives and wild grapes. But their most remarkable activity was gathering the heads of wild barley, oats and wheat which they ground into flour on a large slab in one of the huts.''
This was cooked on hot stones into a sort of flat bread, still common in the region.
At Ohalo II there was also a burial of an approximately 40-year old man who was 1.73m tall.
''We can reconstruct his likely dietary components from the floral and animal remains, but not the proportions. That is as close as we can come to the real paleolithic diet,'' she said.
Since then more grinding stones and starch granules have been found at other paleolithihc sites, including a new finding at Haua Fteah cave in northeast Libya from 31,000 years ago, pushing the date of the use of wild grains back another 10,000 years.
''They used grass seed resources and seed-grinding stones. Researchers identified 15 starch granules and 10 were from goatgrass, Aegilops sp, which is one of the ancestors of domesticated bread wheat.''
Obviously there's more information about the real paleolithic diet to come as the ability to identify these tiny granules of starch improves, Prof Leach says.
''I would agree it is too easy to earn money while sitting at a desk and load up the car with food at the supermarket. But you don't need to go back as far as the paleolithic to find humans expending significant physical energy on the food quest. I would suggest the uncoupling of energy intake and output became marked only with the advent of fossil-fuelled vehicles.''