Saturday, 13 February 2010

The paleo/primal paradigm can be all wrong

The Paleolithic diet/lifestyle paradigm draws from evolutionary theory. In fact, it is based on the validity of Darwinism. While I am hardly a creationist, I maintain that established truths are not necessarily the only truths, attempting to falsify, rather than confirm, in line with scientific method. The first take on the issue was here, below are some more thoughts.

Switch from vegetarianism to Paleo has done me good and there are other testimonials and blogs. For me there is no way back. But is may be premature to draw generalised conclusions. After all, healthy non-Paleo (and high carb) eaters might have never been considered in the equation as a comparison group. While people with metabolic syndrome or other chronic conditions might indeed benefit tremendously from Paleo-like regimen, it does not follow that all people would. There might indeed be some people who thrive on a modern "balanced" and "healthy" diet, and some might be even doing well on SAD. There is no doubt such people exist, the question is: how many and how they can be identified if prevention is to be considered.

Proponents of the Paleo paradigm base their arguments on two critical propositions:
1. Our Paleolithic ancestors ate the diet and had lifestyles which were optimal for their health.
2. Time from the beginning of agriculture (3-10 thousand years) was not long enough for humans to adapt to the new diet/lifestyle.

The problem with the first proposition is that it does not make clear what is meant by health. What was healthy for reproductive success and contributed to physical and mental prowess (more protein, perhaps seasonal abundance of carbohydrates) might not have been optimal for long term health and longevity, where low protein and, perhaps, caloric restriction could be a better choice.

It is the second proposition, however, which is more problematic. True, if natural selection were the sole factor responsible for inheritance, the time was too short. But what if inheritance is not limited to mutation and recombination of DNA? In "Evolution in Four Dimensions" Eva Jablonka argues that there is more to heredity than DNA and genes. In fact, recent publications on epigenetic inheritance appear to be reviving some of the Lamarckian concepts of evolution. Root Gorelick in his "Neo-Lamarkian medicine" speculates that meiotically-heritable epigenetic signals could be transmitted to future generations. Also Arthur Janov makes very interesting observations on the mental health aspects of epigenetic inheritance. A very insightful review of inheritance of acquired characteristics was published in Nature by Yongsheng Liu. Here is another one.

In essence, if indeed Lamarck was, at least partially, right, then perhaps several generations might be sufficient for a simple adaptation, such as lactose tolerance. But lactose tolerance is still not perfect health, we also need time to create adaptations to handle casein digestion, glycation (from galactose), maybe also insulin response. For all this several centuries could have been enough, let alone 3-10 thousand years.

This would fit the observations that different people have different level of tolerance to agricultural diets. In one of my previous posts, I argued that this might have to do with geographic origin of our ancestors. But if epigenetic inheritance were to be responsible for our adaptation to agricultural diet(s), then even few generations can make a difference. If so, then not only geography should play a role, but also the details of out forefathers' menus in the past centuries. We can only infer that indirectly. Were they peasants, artisans, knights, noblemen? Were they rich or poor? After all, it might be the case that they ate hardly any carbohydrates until the 20th century and even then not on a regular basis.

But it gets more complicated than that. Even if environmental signals can indeed translate into inheritance bypassing natural selection (something Darwin believed to be the domain of the future of evolutionary theory) then there are two possibilities:
1. The environmental (dietary) impact is nocuous and induces permanent pathological change, which becomes inherited.
2. The environmental (dietary) impact is challenging and induces adaptation. This can be achieved by activation or amplification of genes (e.g. responsible for free radical scavenging in response to oxidative stress from intensive exercise), which can then be passes by epigenetically. This adaptive response is sometimes described as hormesis, and it applies to low level exposure to normally very harmful factors, such as ionising radiation.

If the impact of agricultural diet was not overwhelmingly harmful (after Darwinian selection took care of the infertile high-carbohydrate early farmers' children), but could be considered a low level stressor instead, then hormesis and epigenetic inheritance could be responsible for adaptation. This might have been the case with knights and nobles, who hunted and/or had more meat on their tables. This could have also applies to fishermen or the poor who nevertheless had ample access to cheap herring. Now, metabolism of peasants who had to subsist on gruel, bread and later potatoes, may have been devastated by excess carbohydrates. Metabolic defects (such as hyperinsulinemia) might have been perpetuated in offspring. But then again some of them managed to poach some small game, gather snails, eggs, and supplemented with plenty of green leafy vegetables to keep metabolism in balance, which would in effect simulate hormesis.

Indeed, if one's ancestors were predominantly grain eaters or vegetarians and their metabolism adjusted with no clinical manifestations, then it is possible than going Paleo with large amounts of meat constitute a new environmental stress! Small amounts of meat would lead to hormesis, but large amount would be overwhelming leading to cancer and early death.

Now, how to we fit Pottenger's cats into the picture?

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