Paleo-hypotheses
In my post on Marlene Zuk’s Paleofantasy, I referred to a review by John Hawks. Hawks suggested that Zuk’s fantasies should be thought of as hypotheses to be tested. I was not convinced that Zuk used this approach, but Hawks’s comment triggered me to write a list of what are the most interesting questions about the paleo lifestyle that I would like to see more evidence on. The list is below.
The common thought that runs through them, beyond Zuk’s points about recent evolution, is that adaptation to a particular diet doesn’t mean it can’t be improved. Also, humans faced broadly varied diets in our past, so I expect that humans have much flexibility in what we can eat.
I should also note that I am posing these questions not as a challenge to the central tenets of the paleo diet, which I expect will largely hold. However, if the answers to these questions fall a certain way, the resulting dietary recommendations probably won’t be called paleo.
Finally, while there is already evidence on the likely answer for some of them, the questions are far from closed.
How does the performance of our mental hardware vary across different diets? I ask this for two reasons. First, we haven’t only evolved physically since the dawn of agriculture, but also mentally. Second, while the paleo-diet may be a good starting point, there must almost certainly be some ways it can be improved, particularly in the context of specific domains such as intelligence. [For me, this is the question I’d most like to know more about.]
How does the paleo-diet compare to the Mediterranean or the Okinawan diet in terms of longevity? Or other health measures? Evolution doesn’t shape humans to live as long as possible. It shapes us to have viable offspring. I should also throw in the growing evidence that the costs of carrying some extra fat are not as high as some people claim.
Following from this, what are the trade-offs? If a diet full of red meat improves health and reproductive success at some age points, does it increase cancer risk in old age? Is there a trade-off between physical and mental output? I am skeptical of claims of a world without trade-offs.
On the flip side to the above two points, what of Michael Rose’s argument that traits at different ages may not be directly linked, and selective forces act more strongly when we are young? Is a paleo diet more beneficial during old age, as the selective forces associated with agriculture have had less opportunity to shape traits that express when we are old? If we switch over to a paleo-diet at age 40, what costs of our pre-40 behaviour persist?
While there is plenty of evidence about the potential for human evolution since the dawn of agriculture, the potential for evolution of our microbiome is orders of magnitude larger. What is the effect of the changes in our microbiome? If someone eats a paleo diet, their microbiome is considerably different from when they were eating a diet full of sugar and grain. But how much does a paleo-diet microbiome today resemble the human microbiome of tens of thousands of years ago?
Grass seeds tend to be poisonous. But how much has the level of poison changed since humans commenced farming grains relative to our ability to digest those poisons? There is likely to have been significant evolution of grains if less poisonous varieties were selected for (and communities that farmed them would likely have had an advantage). Is rice really that bad?
How much of the benefit of the paleo-diet comes from simply excluding sugars and highly processed flour? If you read the paleo testimonials on sites such as Mark’s Daily Apple, I’m guessing most of the benefits came from cutting out the junk and getting some exercise. I’m sounding like Marlene Zuk here, but I’d like to see this tested.
How much of the benefit of the paleo-diet is due to calorific restriction? When the muffins or donuts get passed around at work, you say no. Not only are you excluding simple carbs, but you are also consuming less calories than you might have otherwise.
If we remember that most people hanging out on paleo-websites are the people for whom the diet works, what is the actual rate of attrition of people who chose a paleo diet as opposed to other diets? I know that I find the paleo-diet to be an easy to use heuristic, but is this the case in general?
How do the answers to these questions change as we look at people of different ethnicity with different agricultural histories? How much variation is there within these groups?
And an exercise question - how much variation is there in feet type between people and populations? Is barefoot running better for some people’s feet than others?
I’m sure I can come up with more, but these will do for the moment. Explorations of some of these questions would probably make a nice blog post, so I’ll revisit some of them soon.