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Comment by michaelkeenan | Hacker News Reader

> 10,000 years isn't enough time for humans to adapt to eating grains, so we should eat like cave men instead

One of the details of that argument is that grains contain phytic acid[1], which humans can't digest. Phytic acid binds with important minerals, such as calcium, magnesium, iron, and zinc, making them unavailable when digested. Cows, sheep, goats, and other non-humans produce various phytases, enzymes that digest phytic acid, but humans don't. Some people (such as Marlene Zuk, author of Paleofantasy, recently linked on HN) say that 10,000 years is enough to adapt to a new food, and cite lactose tolerance as an example. But lactose tolerance is the result of a single SNP, which can occur in at least two places. To digest phytic acid, humans would need to evolve a whole new enzyme. You need more than 10,000 years for that.

[1] http://en.wikipedia.org/wiki/Phytic_acid

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Yes, much like every other food on the planet, grains do contain certain compounds that can be harmful when isolated and consumed in large quantities. Did you know fruits and vegetables contain arsenic?

Despite what the Paleo crowd would have you believe, phytates do have health benefits (like fighting cancer and inflammation). And even if they didn't, soaking and cooking grains reduces their final content of phytic acid. Unless you have a very poorly balanced diet that consists almost entirely of grains, phytates are of no concern at all [1].

[1] http://www.drweil.com/drw/u/QAA400758/Are-Phytates-Bad-or-Go...

Two things:

10,000 years is totally enough time for evolution to work on humans. See: lactose tolerance.

Just as importantly, we've been evolving the living daylights out of every domestic plant via selective breeding for just as long. Wild potatoes are poisonous, as are almonds. Maize started out with tiny grain. Apples have been bred into a bazillion varieties, with different sizes, tastes, and textures.

It's silly to say that it's more natural to eat cauliflower than corn, when neither properly existed 10,000 years ago.

See: lactose tolerance

GP specifically mentioned that and dismissed it with a seemingly reasonable argument; care to respond to that? Besides, most humans are not lactose tolerant as adults. Has there been any research concerning a putative phytic acid tolerance? If so, have we identified a particular set of relevant genes? Have we studied the incidence of these genes in various populations?

I sort of assume that humans can handle most compounds they eat on a regular basis, but it seems that many compounds are harmful when consumed in excessive amounts.

Yeah, that was a product of my poor reading; mea culpa and my apologies.

But I do think it is wrong to dismiss lactose tolerance as an example of recent adaption: most adaptations start as a single mutation with a selective advantage. It is disingenuous to claim phytic acid would require "a whole new enzyme", because if an enzyme were evolved specifically to break it down, the way it'd happen is that an existing enzyme would be duplicated (and there's a healthy amount of duplication in the typical genome to start with) and a small number of mutations would specialize this copy for phytic acid. It could be a single mutation on an already duplicated gene; it could be a series of one or more random mutations followed by the final mutation which begins to exert a selective pressure.

But all this is predicated on there being a selective pressure to digest phytic acid. For lactose, there is a strong selective pressure. For diet-related prion disorders (kuru), there is a strong selective pressure. Is there a strong selective pressure to digest phytic acid? Maybe there is, and the adaptation requires too many mutations to reach. Maybe there isn't, and so there is no selective pressure to drive an adaptation.

If I am taking the position that grains aren't that bad, then I am also taking the position that phytic acid -- as it is found in our diets -- isn't particularly bad. Hence, my position must be that there is no strong selective pressure to begin digesting phytic acid, anymore than there is to begin producing our own vitamin C.

The difference is that the evolution for lactose digestion involves turning off an already existing gene. Digesting phytic acid involves evolving a new gene - a new enzyme maker. So you are talking about one random mutation vs. XXXX mutations.

A genetic study has found that humans did evolve rapidly in the last 10,000 years, but most of the changes were one-off mutations such as these.

So... aren't there any bacterial cultures living in the gut that do the digesting for us? Just like how gut bacteria have been found among some Japanese island populations that help digesting seaweed?

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