Why Aren’t Humans Adapted to Grains?

July 10, 2012 in Categories: , by

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A paleo diet is often presented as “eating the foods that humans evolved over 2.5 million years to eat for optimum health”.  I am guilty of presenting this explanation myself.  It’s an easy sound bite and resonates on an intuitive level for the scientifically-inclined.  However, this easy definition of the paleo diet renders the entire diet vulnerable to a common criticism.  While we claim that humans are not adapted to those foods that only became a part of our diet with the advent of agriculture, (specifically grains, legumes and dairy), many refute this claim (and provide scientific evidence of adaptations!).  While the sometimes vehement debates over the merits of a paleo diet are moot to most of us (we know it works for us and that’s enough!), this criticism of what many people think of as a cornerstone of the paleo diet is absolutely valid.

The speed in which a species adapts to a change in environment (which might include anything from predators, to weather, to food sources) depends on something called evolutionary pressure.  Any factors that reduce reproductive success in a proportion of a population influence the genetics of that population–this is evolutionary pressure.  This pressure “selects” for certain genetic traits that increase survival of the species.  Survival, in this case, means health of the individual sufficient to reproduce.  What happens after reproduction doesn’t exert pressure for genetic adaptation. 

The period of time since the advent of agriculture is fairly short in terms of the length of time that humans have been evolving; however, it is absolutely enough time to adapt given sufficient evolutionary pressure.  Dairy consumption is an excellent example of a way in which humans (at least a proportion of them) have adapted to a new food source over a short period of time.  Lactose tolerance and lactose persistence (ability to still digest lactose as an adult) is present in 80% of humans of European and American descent, which means that 80% of European and American individuals contain the genes for the enzyme lactase.  These people are descendants of lines in which adaptation has occurred (in conjunction with dairy consumption, which might be why this adaptation has not occurred to such a high degree in other cultures) 1.  If humans continue to consume dairy products, the percentage of people who contain the gene for lactase will gradually increase until everyone is lactose tolerant and lactose persistent.  Dairy may still not be an optimal food (casein is highly allergenic; milk contains protease inhibitors), but this adaptation is the chief reason why the exclusion of dairy from the paleo diet is so contentious (especially when considering raw, grass-fed dairy).  Indeed, the scientific literature is divided between studies showing that milk is beneficial for our health versus detrimental for our health (for a great summary of this argument see http://chriskresser.com/dairy-food-of-the-gods-or-neolithic-agent-of-disease).

The same process of adaptation is happening as we speak with regards to grains.  For example, since the advent of agriculture, humans have increased the number copies of the genes for salivary amylase, the enzyme in our saliva that starts the digestion of starch as we eat 2.  However, the scientific literature has more conclusively established a link between the dietary lectins found in grains, especially gluten, and a huge variety of health conditions (see The Paleo Answer).  The incidence of celiac disease and gluten-sensitivity is increasing (and some studies predict that they are still very underdiagnosed) 3,4.  There is a growing body of scientific literature linking gluten sensitivity to autoimmune disease 5,6Yes, there is genetic adaptation, but human health is still indisputably negatively affected by consumption of grains.  Gluten likely causes the telltale damage to the gut lining seen in celiac disease at least to some degree in most individuals (obviously, there is huge variability here).  Once study author wrote “If you look for coeliac disease you will find it” 4

It’s not that humans haven’t adapted to eating grains; it’s that humans haven’t fully adapted to eating grains. Evolutionary pressure is relatively low because the health effects of grain consumption doesn’t change reproduction rates dramatically.  However, it is very likely that there are people out there who are carrying a set of genetics that does make them adapted to eating grains.  This is why when someone tells me that they are completely healthy no matter what they eat, I simply congratulate them.  They may be adapted to Neolithic foods (they might also be even healthier on a paleo diet, but they aren’t likely to try it if they feel so great now, so I don’t belabor the point).  And, given enough time, humans will adapt to eating grains and will eventually thrive on its consumption.  But you are not going to change your genetics.  If you are part of the majority of humans who do not carry complete genetic adaptations to grain consumption, you are better off without it.  Depending on where you are in the spectrum, you may never be able to tolerate even small amounts or you may be able to incorporate regular cheat meals into your diet with little harm. 

The answer to this question is not straight forward.  10,000 years is insufficient time for humans to have fully adapted to thisnew food source.  Basically, humans are adapting but are not yet fully adapted.  So, you get to choose.  Do you want to eat a diet that you are not fully adapted to in the hopes that your genes will contribute to the eventual complete adaptation of our species to this diet?  Or do you want to live the healthiest life you can now?

1 Enattah N et al. “Evidence of Still-Ongoing Convergence Evolution of the Lactase Persistence T-13910 Alleles in Humans”. The American Journal of Human Genetics  2007. 81(3): 615–25.

2 Wilson, David S. (1994). “Adaptive genetic variation and human evolutionary psychology”. Ethology and Sociobiology 15 (4): 219–35. DOI:10.1016/0162-3095(94)90015-9.

3 Caproni M, et al. Celiac disease and dermatologic manifestations: many skin clue to unfold gluten-sensitive enteropathy.  Gastroenterol Res Pract. 2012;2012:952753. Epub 2012 May 30.

4 Aziz I, Sanders DS. Are we diagnosing too many people with coeliac disease? Proc Nutr Soc. 2012 May 3:1-7. [Epub ahead of print]

5 Fasano A. Zonulin, regulation of tight junctions, and autoimmune diseases. Ann N Y Acad Sci. 2012 Jul;1258(1):25-33.

64 Korponay-Szabó IR et al. Gluten-dependent intestinal autoimmune response. Curr Pharm Des. 2012 Jun 21. [Epub ahead of print]


And, we have to consider, is wheat evolving quicker than we are? Modern wheat has been so changed and adapted that it has little in common with the wheat from 60 years ago let alone the wheat that the first farmers would have been eating.

If our adaptation to wheat was getting better, our incidences of celiac and such diseases should be getting less but they seem to be skyrocketing. Even with increased with diagnosis it would seem that things are getting worse and not better so I know for sure, that wheat, will never be a part of our diet again.

Great article as ever. :)

This was great–very informative and easy to understand.

I’m not sure if you know this yet or not and I didn’t want to post it on your facebook page, but I got an email from the crohnsdad website this morning. It was from Laura, Alan’s daughter, saying that he passed away on Sunday morning. It’s such sad news–he will be terribly missed. Just thought I should let you know.

You’re welcome. I was so looking forward to the collaborative posts with you two but the universe had other plans. I still have a hard time believing this happened. Thank you for taking the time to respond–I really appreciate it.

Actually, evolution of digestive capabilities can happen extremely rapidly due to the activities of commensal bacteria in our small intestines. We all carry about 500 species of these bacteria, and the exact consortium differs within individuals, and especially among populations. For example, Japanese tend to have marine (ocean) bacteria, presumably because seaweed is part of their diet. Our bacterial populations can change during our life, sometimes extremely rapidly. I am not aware of contributions of bacteria to milk digestion, but for grain digestion, I think there is a good deal of evidence. And as for Crohn’s disease, fecal transplants (yuk, but look it up, transferring bacteria from gut of healthy person to gut of sick person) have been able to cure it. There is much we do not understand, but I think the Paleo community should refrain from issuing blanket evolutionary justifications for the diet that happens to work for them.

Oooh, that’s cool about the gut flora. I will look into that some more. Do you have references? I’m specifically interested in the case of antibiotic use. I agree completely with your last point(and Thursday’s post will actually expand on defining paleo without the evolutionary argument).

You’re welcome. I was so looking forward to the collaborative posts with you two but the universe had other plans. I still have a hard time believing this happened. Thank you for taking the time to respond–I really appreciate it.

Good article. The only comment I would make is that I don’t believe humans will ever adapt to grains as the grains keep changing and are being “evolved” into super grains and now with the push for GMO grains they will change even faster and our bodies just have no chance to try and catch up much less keep up. I love reading your blog – great job! Kris W.

Is there any evolutionary pressure on humans to continue adapt to grain consumption (?) Perhaps a small amount, but the brunt of the diseases of civilization hit after prime reproductive years, and now humans are much more likely to have only a few children. Those few children we do have will be cared for by the state in the case of the death of the parents, and you can survive quite well in an ill state (most of the time). Thus health in a person’s mid life is much less of a factor in determining the “fitness” of an individual from an evolutionary (reproductive) perspective.

While the microbiome of the gut has the capability of evolving much more quickly than our primary genome, again, the pressures for it to do so are also limited by modern society.

Hi Sarah! I’m trying to print out all your “why” articles to make a big binder for my family, hoping they’ll be around and read some stuff. The green “print” button at the bottom of the article doesn’t work for me, I’m trying to click it but nothing happens.

I like that you actually admit the truth about evolutionary pressure! I am post-menopausal and my daughter will turn 30 in a few days – so evolution is DONE with me. The problem is, I’m not done with myself!

Men remain potentially useful in an evolutionary sense even if they live into their 100s. Women – not so much. I’ve heard arguments that having a few elderly women around benefitted the tribe overall as there was someone to pass along wisdom and assist mothers. But even if that is an evolutionary advantage to a tribe, you only need a handful of crones, the tribe mostly needs maidens and mothers…

I don’t CARE what is “natural” because there’s nothing in nature than requires the presence of 50 yr old women, but I LIKE me! ;)

Thank you for this. Very interesting.

Just to join the discussion about the gut microflora. Yes, it can adapt very quickly – in a matter of weeks, actually, if a diet is changed dramatically. But it is the by products of microbial activity that enter our system and affect our health. And those will not change because the composition of our gut microflora has changed. If we eat certain things, the by products of their digestion will appear and affect us.

Also gluten is a protein and thus doesn’t really play any role in gut microbial activities as their nutrient source is mostly carbohydrates.

Thanks for bumping this older article on FB! I hadn’t seen it before and it is a really wonderful and simple explanation.

I agree almost entirely with this, but was wondering about one point: the evolutionary pressure. I was under the assumption that only if a mutation was BENEFICIAL to reproduction would its presence increase in prevalence. For example: if your body all of a sudden adapts to drinking milk, you have a steady source of nutrients and can be healthier and will have children more easily, and will therefore likely have more children. But in the case of grains, it’s damaging our systems so much, it’s decreasing our reproductive ability. Is the point more that those with gluten/grain issues will simply start to die off (a harsh way to put it, but may people with celiac and associated Hashimoto’s disease simply can’t have children, at least not without intervention)? Or are we talking about something other than mutation, as was alluded to by some other commenters? Some mechanism that allows our gut flora to adapt to new foods that previously harmed it?

I think evolutionary pressure is much less significant in a modern world where that kind of intervention is available. Good and bad genes will get passed on because so many are able to conceive whether they’re healthy enough to do it or not. And, autoimmune disease, obesity, diabetes, etc. are not always genetic conditions: They can be caused by poor diet and environmental triggers as well, so if neither of those factors are addressed, you have an increasingly sick population whether they had “good” genes to begin with or not. – Christina, Sarah’s assistant

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