Thursday, August 25, 2011

Adapted to Neolithic Foods?

A while back, Stephan Guyenet pointed to this excellent paper by lead author Pedro Carrera-Bastos (which included Loren Cordain and Staffan Lindberg), that I just got around to reading. It's pretty straightforward paleo stuff, neolithic foods are bad, modern industrial foods are really bad, modern lifestyles, inadequate sleep, smoking, stress, lack of vitamin D, really, really bad, etc.

But what's really interesting is Stephan's take on it. He writes:
One of the things I like most about the paper is that it acknowledges the significant genetic adaptation to agriculture and pastoralism that has occurred in populations that have been practicing it for thousands of years. It hypothesizes that the main detrimental change was not the adoption of agriculture, but the more recent industrialization of the food system. I agree.
Uhm, what? I just read the paper and I didn't see anything in it about acknowledging significant genetic adaptation to agriculture and pastoralism. I did see this:
This is why it is being increasingly recognized in the scientific literature, especially after Eaton and Konner’s seminal publication in 1985, that the profound changes in diet and lifestyle that occurred after the Neolithic Revolution (and more so after the Industrial Revolution and the Modern Age) are too recent on an evolutionary time scale for the human genome to have fully adapted.

In fact, despite various alleles being targets of selection since the Agricultural Revolution, most of the human genome comprises genes selected during the Paleolithic Era in Africa, a period that lasted from about 2.5 million years ago to 11,000 years ago.
What part of that indicates significant adaption to agriculture? The paper goes on to say:
Finally, the fossil record suggests that when hunter–gatherer populations made the transition to an agricultural pattern of subsistence, their health status and lifespan decreased.
As I've written before, Stephan has long been a proponent of traditional diets: neolithic foods are great, perhaps (probably?) optimal, as long as they are prepared in a traditional manner that minimizes anti-nutrients and such. The underlying assumption being that we are significantly adapted to these foods. The fact that Stephan is reading into this paper something that simply isn't written there is a classic case of confirmation bias, in my opinion. Stephan corresponded with Pedro on this paper and is consequentially cited by Pedro, so maybe I'm missing something, but I don't see a single sentence that indicates anything about significant adaption to neolithic foods.

I do see things like this:
The Agricultural Revolution began about 11,000 years ago in the Middle East, later spread to other regions of the globe, and drastically altered the diet and lifestyle that had shaped the human genome for the preceding 2 million plus years. Some of the more significant dietary changes were the use of cereal grains as staple foods, the introduction of nonhuman milk, domesticated meats, legumes and other cultivated plant foods, and later widespread use of sucrose and alcoholic beverages.

Nevertheless it was the Industrial Revolution (with the widespread use of refined vegetable oils, refined cereal grains, and refined sugars) and the Modern Age (with the advent of the “junk food” industry, generalized physical inactivity, introduction of various pollutants, avoidance of sun exposure, and reduction in sleep time and quality coupled with increased chronic psychological stress) that brought about the most disruptive and maladaptive changes, which may have serious pathophysiological consequences. For instance, chronic psychological stress, environmental pollution, and smoking are associated with low-grade chronic inflammation,
which is one of the main causes of insulin resistance.
I think every paleo/primal author/blogger would agree with this. Neolithic foods suck, additional modern/industrial foods (frankenoils, processed foods, etc) really, really suck. And a modern lifestyle, especially constant low-level stress, takes its toll. One can speculate all day long about what a pre-neolithic diet consisted of, that's not my point. As the paper points out:
Importantly, 11,000 years represent approximately 366 human generations, which comprise only 0.5% of the history of the genus Homo (Table 1).
Is 366 generations long enough to adapt significantly to neolithic foods? Mutation rates are a hot topic right now in biology and anthropology. They now appear to happen at a slower rate than previously thought. John Hawks wrote last year:
The study was by Jared Roach and colleagues, and as you might guess from my post title, the result was surprising. Previous work had suggested a human mutation rate around 2.5 x 10-8 per site per generation. The new study found less than half the expected number of mutations between these parents and offspring, an estimated rate of only 1.1 x 10-8 per site. 
Yesterday Hawks blogged about another paper that seems to back up a slower than previously thought genetic mutation rate:
A new paper in Nature by Zhe-Xi Luo and colleagues reports the discovery of a 160-million-year-old early mammal, Juramaia, which they attribute to the placental mammal lineage. The news aspect is that this extends the chronology of fossil placental and marsupial mammals (the sister clade of placentals) by some 40 million years. That's a big chunk of time, but it's a really nice fossil which seems pretty clear in its morphology.

I'm reading this closely because of the effect on the interpretation of mutation rates and the molecular clock. Obviously, if the earliest evidence for placental mammals used to be 120 million years ago, and now it's 160, that should affect the way we approach the genetic divergence of mammal lineages. In particular, when it comes to primates, some modern lineages are represented by fossils relatively early in the Cenozoic, suggesting that the common ancestor of all the primates may have been much earlier, deep in the Cretaceous period. 
On the other hand, maybe it just takes a few simple mutations to adapt to neolithic foods (prepared in a traditional manner, of course). It only took one mutation to turn off lactose intolerance, and that mutation has occurred in several populations engaging in animal husbandry independently.  But that mutation is to simply continue the production of lactase. Humans, like all mammals, are already ridiculously well-adapted to milk--at least their own species' milk, not processed, when in infancy--beyond that, things can get dicey. How many mutations and selection are necesary to adjust to a diet heavy in grains, legumes and other neolithic cultivars?

How well adapted we are to neolithic foods, which the paper cites as:
[...]cereal grains as staple foods, the introduction of nonhuman milk, domesticated meats, legumes and other cultivated plant foods, and later widespread use of sucrose and alcoholic beverages. [ed. I see sucrose as more of a modern/industrial era food]
Who knows, but one is probably better off avoiding them all as much as possible. I'm going to stick with this paradigm for now, I don't see the food reward/palatability hypothesis (FRH), especially as evoked by people with a strong bias towards "traditional" foods, as even coming close to supplanting it, or even supplementing it, at this point. Am I specifically going after Stephan Guyenet? Yes, I am. His blog is hugely influential and his recent "takedown" of the carbohydrate hypothesis and endorsement of FRH has been embraced by many influential bloggers. Maybe I'm just being reactionary, and I'm sure I'm guilty of my own confirmation bias, but I'm just not buying it.

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