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Ask a Westerner what their favorite Japanese food is and there’s a high chance that the answer will be sushi. The widespread popularity of the delicately crafted delicacy has made it almost synonymous with the word “Japan”, even though there now exist dozens of different varieties made by people from all over the world.

Many of you reading this will have had sushi, some of you might even love it more than your mom’s cooking, but even so, that doesn’t guarantee that you have the guts for sushi. We’re not talking about the courage needed to put raw fish in your mouth, but rather, the genes required to properly digest seaweed.

Confused? Here’s the science behind it.

Three years ago, Mirjam Czjzek, a chemist at the Station Biologique de Roscoff in France, discovered that Japanese people have a type of bacterium known as Bacteroides plebeius in their guts, which contains an enzyme that helps them break down the carbohydrates in seaweed. Testing a group of 13 Japanese and 18 North Americans showed positive results in five of the Japanese subjects, but none of the North Americans appeared to have the seaweed-munching enzyme in them. The Westerners are not the odd ones here, however, as the enzyme is commonly found only in marine bacteria.

Before you start thinking Japanese people are secretly mutants, let’s make it clear that they didn’t genetically modify themselves in some crazy science experiment. It is speculated that their intestinal bacteria might have gotten friendly with the seaweed-digesting enzymes found in bacteria that live on seaweed itself. The Japanese have a long history of handling the marine algae raw, as an ancient form of currency as well as part of their daily diet up till today. Such day-to-day contact with seaweed apparently gives the human gut bacteria a chance to merge with genetic material from the seaweed-chomping bacteria.

▼ Wakame, a type of green seaweed, is often served in miso soup.
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▼ Seaweed salad containing assorted varieties of edible seaweed.
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But not to worry, you’re not going to get a case of tummy ache from ingesting seaweed even if your body doesn’t posses some of that algae-digesting bacterium. Neither are the Japanese people who have yet to gain such super powers. What the enzyme does is “help Japanese who dine on seaweed get more nutrition from their meal than do North Americans”, Czjzek explains. So it’s offers a helping hand rather than being an essential addition to our bodies.

Oh well, so our non-Japanese bodies may absorb fewer nutrients from seaweed, but at least we don’t have to give up on eating sushi just because our guts aren’t tailored for digesting marine algae!

Well, that’s the long story cut short. If you’re interested the scientific details behind the research, be sure to check out the full article!

Source: Science AAAS
Images: Shinjuku Takashimaya Blog, Inoue Isamu Shouten, Recipe Box