Dr Karl: There are many many diets available today to those of us wishing to lose some extra weight. One current favourite is the so-called 'Palaeolithic diet'.
In a nutshell, it claims that our Palaeolithic ancestors lived in wondrous harmony with their environment, which gave them exactly what they needed to live a long and happy lifestyle.
And furthermore, it claims that the period of 12,000 years-or-so since we invented agriculture is too short for our bodies to have evolved to cope with the new foods that agriculture has given us.
So what is a Paleo-diet? Fruit, green vegetables, eggs, poultry, meat and seafood -- but no dairy, grains, legumes or processed oils.
There are a few problems with this.
First, there were many very different varieties of Palaeolithic diets. Second, we humans have done a lot of evolving in the last 12,000 years. Third, we can't eat what our Palaeolithic ancestors ate anyway -- because that stuff is not around any more. And fourth, the recommended Palaeolithic diet is way out of kilter with dietitians' recommendations.
Let's start with types of Palaeolithic diets. The Palaeolithic spans a period from around two-and-a-half million years ago right up until the invention of agriculture some 12,000 years ago.
When people started writing books about the Palaeolithic diet back in the 1970s, we had only a vague idea of what our Stone Age ancestors ate. But since then our anthropologists and archaeologists have looked at fireplaces, middens, teeth and the actual tools our ancestors used to prepare their meals. It turns out that they ate a very varied diet -- which included insects. We see this in some of today's so-called primitive peoples. While the Inuit of the Arctic have a diet that is 99 per cent meat, the !Kung of Africa eat around 12 per cent meat.
That's a huge range.
So, what else. Well, one cornerstone of the Palaeolithic diet creed is that our bodies could not possibly evolve fast enough in the last 12,000 years to accommodate our new foods.
This is so wrong.
In the last 12,000 years, some of us have evolved to be able to drink milk when we grow into adults, some of us have evolved extra copies of the amylase enzyme so that we can more easily digest starches, while some of us have evolved blue eyes. Others among us, in Africa, have evolved resistance to malaria. With regard to living at high altitudes, three separate groups of humans living in Tibet, the Andes and in Ethiopia have evolved three different methods of dealing with low oxygen. And speaking of food, some Japanese have evolved special bacteria in their gut that can digest seaweed -- so sushi is no trouble at all. So yes, our bodies could easily evolve fast enough in 12,000 years to accommodate new foods.
The third problem with the Palaeolithic diet is that the food eaten back then is simply not around any more. Very few meats are as lean as those our Paleolithic ancestors ate. Today's corn was once a straggly skinny grass, while tomatoes used to be tiny berries. Bananas were mostly filled with seeds until a recent mutation. We have transformed the meat and plant species we eat through millennia of artificial selection and evolution. Consider cabbage, broccoli, brussels sprouts and cauliflower and kale -- they are each wildly different cultivars of one single species, Brassica oleracea.
The fourth problem with the Palaeolithic diet is the nutritional aspects of the diet itself. The recommendation is a high protein intake (19-35 per cent of a person's daily energy) -- which is quite a lot higher than the Australian Nutrient Reference value suggestion of 15 to 25 per cent.
The Palaeolithic diet also recommends a moderate to high intake of fat -- again, not recommended by modern dietitians. The Palaeolithic diet does recommend fibre from vegetables and fruit (which is entirely sensible) but they advise not to eat any whole grains. However, we have very good evidence that 30,000 years ago some of our ancestors were already eating grains and legumes.
But, on the plus hand, the Palaeolithic diet advises against processed foods with added salt, sugars and flavourings -- which is entirely sensible.
Gregor Yanega, a professor of biology at Pacific University in Oregon said: "Our guts are special because they are less specialised. They can accommodate so many changes in the foods that surround us ... we can even eat some of the world's more difficult foodstuffs: grains, leaves and plants. Berries, nuts, meats, sugars, those are easy. Eating them together is pretty rare."
Maybe we should just remember Michael Pollan's simpler advice of "Eat food, mostly plants, not too much."