[ExI] Digestive adaptations

J. Stanton js_exi at gnolls.org
Wed Apr 20 20:02:41 UTC 2011

Spike wrote:
> What do you think of my notion that human groups radiated long enough ago
> that some (limited) digestive system adaptations and genetic drift have had
> time to occurr, which allow some humans to do things with their diet that
> others cannot do?  Seems like there should be plenty of documentation on
> variation of digestive system anatomy within the species.

You're absolutely correct -- just in regard to different issues.

Classic example 1 is celiac.  There is genetic evidence for this in the 
MHC gene complex: the HLA haplotypes associated with celiac are less 
common among populations that have been agriculturalists for longer.
Simoons, F. J. 1981. Celiac disease as a geographic problem. In Food, 
nutrition and evolution, ed. D. N. Walcher and N. Kretchmer, pp. 179–99 
(unfortunately not available online in any form I can find)

Classic example 2 is lactase persistence, i.e. the ability to 
enzymatically digest lactose through adulthood.  (Note that most people 
can digest small amounts of lactose via bacteria in the colon.)  Lactose 
intolerance varies by population from a few percent to basically 100%.

(There is also speculation that an ability to deal well with a 
high-carbohydrate diet is genetically determined to some degree, based 
on the prevalence of obesity and diabetes in recently 'civilized' 
traditional cultures.  However, I'm unaware of any research that 
pinpoints a genetic difference, and many of these effects are also 
epigenetically effected.)

However, as far as ability to digest fat, the obvious counterexamples 
are the aforementioned Inuit (already mentioned) and the Maasai (an 
African tribe of pastoralists who live almost entirely on milk, meat, 
and cow's blood).  In both cases, when traditional Inuit or Maasai move 
to 'civilization' and begin eating Western foods, they suffer 
atherosclerosis and heart disease.

Another example is Australian aboriginals on a Western diet, who have 
one of the worst rates of heart disease in the world despite one of the 
lowest blood cholesterol levels.


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