In A Nutshell
Sushi is one of the most popular dishes in the world, but the raw seaweed and fish can often be difficult to digest, especially due to the fact that plant matter actually cannot be independently digested. Whenever you eat plant matter, microorganisms within your body help break it down. Due to their historical relationship with seaweed, the Japanese are host to bacteria that are specialized to eat seaweed. These microorganisms are not present in other humans.
The Whole Bushel
No animals on the planet are actually capable of properly digesting plant matter, including fruits and vegetables. This rule even applies to herbivores. A major component of plant matter is cellulose, and our bodies are simply incapable of breaking it down.
Well, not without help. You might not be aware of it, but you and the entire animal kingdom are involved in a mutually beneficial relationship with trillions of microbes. In some animals like cows, specific microbes make it possible for them to digest cellulose. In other animals, specific microbes convert cellulose to something that can be digested. Either way, without specialized digestion microbes, nobody would be eating plants at all.
The Japanese have been eating sushi since the eighth century. Of course, a major component of sushi is raw seaweed, the tightly wrapped plant that completes the ensemble. Seaweed is still a crucial part of the typical Japanese citizen’s diet—on average, he or she will eat 14.2 grams of seaweed a day.
It’s no wonder, then, that the Japanese have specialized bacteria, known as Bacterioides plebeius, in their digestive system to help with the breakdown of seaweed. This mutually beneficial relationship has been cultivated for centuries, a fine-tuned product of natural selection.
How did the bacteria get there in the first place? There were already microbes feeding on the seaweed when they were harvested by the ancient or medieval Japanese. By eating the seaweed raw, the Japanese gave the bacteria the chance to swap genetic information with microbes already living in the stomach of the Japanese—or simply played host to the alien bacteria.
Bacteriodes plebius are also found in the stomachs of bugs that feed on seaweed. They are not found in other humans. By breaking down seaweed more effectively, the host can derive more energy from seaweed.
Seaweed is high in dietary fiber. It is also a source of iodine, vitamin A, vitamin B-12, calcium, protein, and healthy fats.