Food Geek

Maki Sushi
Originally uploaded by ric_w

Complex sugars can be difficult for humans to digest.  Indeed, many of the complex sugars that we "digest" actually aren't digested by us, they are digested by the plethora of bacteria that live in our guts.  We provide a warm home for them, and a steady supply of food.  They provide metabolic capabilities that we don't possess.

A really unique study was published last week in the journal Nature demonstrating that the bacteria in the guts of Japanese people possess the metabolic ability to digest some complex sugars that are present in seaweeds.  The Japanese diet is quite high in seaweed - 14.2 g/person/day.  You add that up, there's a lot of seaweed sugars passing through a lot of bellies in Japan, every day.  

That presents an interesting evolutionary environment.  If there is a nutrient that is going unused, some bacteria will move in there and start using it.  In the case of the Japanese, what they have is that the genes that allow degradation of these seaweed sugars have passed from bacteria that normally live in the ocean on seaweed, and have moved into another bacteria that is a major inhabitant in the human gut (Bacteroides).  Probably these bacteria encountered each other in the gut, and some genes were passed from the seaweed bacteria  to the gut bacteria.  Cool!  This provides the Bacteroides with the ability to grow on seaweed sugars that it normally can't use.  One would predict that a Japanese person with this Bacteroides in their belly would be able to extract more calories from a sushi roll than someone of European descent who doesn't carry this bug.  (Incidentally, the major groups of bacteria that live in your gut are set up in early childhood, and don't shift much over your lifetime - so even if you as an individual eat a lot of sushi, you probably haven't picked up the bacteria that will allow you to degrade the complex sugars in seaweed).

Anyway, coolness.  Reminiscent of lactose tolerance (subject for another post), we have a whole population of human beings that is able to degrade a unique group of sugars that are prevalent in their unique diet.