The most commonly eaten (and researched) are the brown varieties such as kelp and wakame, followed by red seaweed, which includes nori (yep — that’s what most sushi chefs use).
While seaweed-based cuisine has a proud history in many Asian countries, Japan has made it into an art form, employing over 20 different species in their fare. In a restaurant, you’re most likely to consume seaweed in a small kelp (kombu) salad, simmered into miso soup, or wrapped around a sushi roll.
At just two tablespoons per serving, it’s true that seaweed isn’t a realistic source of many vitamins, and its benefits can occasionally be exaggerated.
Seaweed contains vitamins A and C, and is also a source of calcium.
The benefits of this sea green extend far beyond basic nutrition: Research suggests seaweed can also help regulate estrogen and estradiol levels — two hormones responsible for proper development and function of sexual organs — potentially reducing the risk of breast cancer. In fact, some claim Japan’s high seaweed consumption is responsible for the country’s conspicuously low incidence of the diseases. For the same reasons, seaweed may also help to control PMS and improve female fertility issues.
And many studies have shown seaweed is an extraordinarily potent source of antioxidants and also helps prevent inflammation (a contributor to arthritis, celiac disease, asthma, depression, obesity).