Why do Japanese people get more out of their sushi?

Why do Japanese people get more out of their sushi? Sushi is raw fish and rice, of course, but also commonly included the seaweed called nori. Nori is actually a giant form of marine red algae of the species Porphyra, and contains complex carbohydrates called galactans which humans can’t digest, because we don’t have a gene for making the right “galactanase.” There are marine bacteria called Zobellia galactanivorans that do make the necessary enzyme, and feed on the algae. When a group of scientists examined the microbiomes of people from around the world, they found that the Zobellia enzyme has become transferred to the common intestinal bacteria Bacteroides plebius. But only in Japanese people! Who, we presume, because of a diet rich in uncooked sea products, acquire Zobellia at some time, which then, through their pili, share the gene for the galactanase with their new neighbors. So we all can eat nori, but most Japanese can also digest it.

Story source: Transfer of carbohydrate-active enzymes from marine bacteria to Japanese gut microbiota. Jan-Hendrik Hehemann et al.Nature464, 908-912 (8 April 2010) | doi:10.1038/nature08937. Sushi: Image by Tony Gladvin Georgevia Flickr. CC BY 2.0