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.

  1. 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.]
  2. 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.
  3. 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.
  4. 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?
  5. 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?
  6. 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?
  7. 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.
  8. 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.
  9. 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?
  10. 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?
  11. 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.

9 comments

  1. Have you checked out Melissa McEwen’s blog? http://huntgatherlove.com/ She strikes me as rather knowledgeable about everything food including paleo. (She also wrote a very good review of Zuk’s book). Just reading through your list of hypotheses, I have these vague thougts she may have thougth and written about them.

    1. I think I’ve been there before, but I’ll have to revisit. I’ve seen a lot of discussions on some of these questions – I’m just not sure the evidence on many of them is very good or points in a clear direction.

  2. Excellent post my man! Now THESE are a set of very good properly critical scientific questions.

    Questions 7 & 8 were points that were made by Steven Guyenet, and also noted on my blog:

    Fun Facts About Obesity | JayMan’s Blog

    #9 applies for a lot of things, not just the paleo diet (*cough* “game” *cough*).

    Question 10 is another big question I’d like to see answered as well.

    1. A sub-question I might ask relating to Guyenet’s point would be whether any of the diets tend to make the person less likely to eat more as they feel less hungry. People on paleo diets keep stating this to be one of the main benefits, and it matches my experience from personal experimentation, but again, I’m not sure it’s a general fact.

  3. The paleodiet is very similar to Atkins’, New South Beach and Diabetes II diets. The main point of these diets is that sugars and starches screw up our insulin regulation so that we eat more. All of these diets rely on Atkins’ glycemic index to regulate we eat. The net result is relatively fewer carbs and more protein fat. Atkins is not concerned about what kinds of fats or proteins we eat, but the other diets are.

    Atkins is plagiarized by everyone and cited by no one, so many of the people in the paleodiet field have never heard of him.

    1. I agree, that there is a considerable part of the paleo community that advocates low or moderate carb versions of the diet, but to equate paleo with low carb goes too far. There is little or no proof that a palaeolithic diet was actually low on carbohydrates.

  4. Congratulations. Your list is a very welcome move towards proper, dispassionate scientific enquiry and away from the speculation, dogma and ya-booism that currently afflicts paleo debate.

    But before we can get much further along that road, we may need at least SOME consensus on one of the most vexed questions of all: What IS “the” paleo diet? Or rather, is there any such thing, since as you rightly say “humans faced broadly varied diets in our past”?

    I see very little useful consensus at the moment on what proportions of macronutrients were consumed by early paleo populations, whether these were predominantly from plant or animal sources, and whether they included substantial, nominal – or nil? – amounts of contentious items such as tubers and grains/grasses. Some folks even argue over a paleo role for alcohol, despite its prima facie dependence on the availability of farmed grain. Among common food groups, perhaps only dairy is completely excluded from debate as a paleo item (Loren Cordain: “Wild animals cannot be milked”.)

    Absent better definition(s) of (the) paleo diet(s), it’s going to be hard to get much clarification on any of your questions except maybe #3 (specific risk/reward of heavy red meat diet) and #11 (role of exercise).

    Tentatively, I suggest what we may need is a similar approach to that outlined in one paper on “the” Mediterranean diet: there being no such single, definable entity, future studies should specify which variant they’re based on by both locale and date, e.g. “the Cretan diet 1948″ or, in this case e.g. “Neanderthal diet c50,000BCE”, to allow for reasonable precision in specifying the macronutrient ratios and sources of the foods/drinks consumed.

    Personally, as I’m now well into middle age, I’m most interested in your question #2 about the longevity benefits of different diets. Longevity diets on which we have the best data all seem to lean heavily on (a) veg/fruit (b) the products of farming such as whole grains, but make very limited, if any, allowance for farmed red or processed meats.

    It doesn’t make sense to me that ANY version of a paleo diet would turn out to be optimal for longevity, for the very good reason you give: “Evolution doesn’t shape humans to live as long as possible. It shapes us to have viable offspring.” (And day to day, I imagine strength and energy might have vital for paleo males, but diet-based longevity of no concern at all.)

    Which is why I found your putting the opposite argument, in question #4, very stimulating.

    As indeed I did your whole article. My thanks and, again, congratulations.

    Wishing you enduring health

    Ivor Goodbody

    1. Thanks for your note Ivor. I agree on the definitional issue. One point that Zuk does hit on well is that humans had huge variation in diet. However, it’s possible to see a lot of common threads among the different diets. But whoever does this research will have to think about the definition as any experiments that don’t turn up the results people want will be criticised for not being a true paleo diet.

      I recommend spending some time on the 55 theses website that I linked to – as the title suggests, it lays out Rose’s 55 theses at the foundation of his argument. There’s a lot of interesting information in there.

  5. “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.”

    All those programmers drinking mountain dew probably do it to keep their blood glucose levels real high so that they can work better. But, whatever. Don’t do that.

    “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. ”

    There is probably a lot too this. In my mind I just lump paleo with the other low carb diets.

    Atkins wasn’t even the first:

    http://www.bodybuilding.com/fun/md66.htm

    No joke. If you are fat, low-carb diets will work.

    In general, I think you are overly optimistic about the ability of research to get clear answers on health/diet issues.

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