When it comes to marine plants, none are more common than seaweed. Especially because many of the most well-known aquatic plants including sargassum, kelp, red algae and phytoplankton are all different types of seaweed. In fact, there are more than 12,000 species of seaweed within the world's oceans, seas, lakes and rivers – all serving various functions such as producing oxygen, providing shelter and being a food source for marine life. They also fertilize other marine plants, filter pollutants and reduce wave action and subsequent erosion.

Seaweed plays a critical role in the world's underwater ecosystem. Its cultivation and mass production for human consumption is also a major plus, since seaweed has many unique properties and proven health advantages that some cultures have known about for thousands of years. "Seaweed is highly nutritious and offers several health benefits," says Amy Goodson, a nutritionist and registered dietitian at The Sports Nutrition Playbook. Such benefits are among the reasons "seaweed is popular in various Asian cuisines such as Japanese, Korean and Chinese," she adds.

How is seaweed prepared? 

As a crop, seaweed is grown and cultivated in seaweed farms. There, it grows on longlines that are suspended around 4 feet to 8 feet below the surface of the water. Seaweed farmed this way usually reaches 10 feet or more in length before being harvested, per the U.S. National Oceanic and Atmospheric Administration. 

After harvesting, the seaweed is "cleaned thoroughly to remove any debris or contaminants," explains Goodson. "It can then be eaten raw, dried or cooked." 

When seaweed is served dry, as most Americans enjoy it, "it's typically blended into a mixture that is poured into a mold before being dried," explains LeeAnn Weintraub, a registered dietitian and nutrition consultant based in Los Angeles. This results in paper-like thin sheets that can be rolled to wrap rice and fish to make sushi, or be soaked in water to be rehydrated. 

Dried nori seaweed sheets are commonly added to foods for flavor, crunchy texture and nutrients. Dried seaweed can also be baked or fried and seasoned "to be enjoyed as chips and snacks," says Caroline Susie, a registered dietitian and national spokesperson for the Academy of Nutrition and Dietetics. 

Various forms of seaweed are also popular ingredients or toppings in or on salads, ramen, miso soup, pizza, smoothies, poke bowls, hummus, tacos, gyoza and stir-fries. Susie notes that seaweed also has a supplement form, underscoring the plant's curative properties. 

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Is seaweed good for you? 

Seaweed contains "antioxidants, copper, potassium, zinc and omega-3 fatty acids," says Susie. Because of these and other nutrients, she says, "research suggests that seaweed may help with heart health, blood sugar control and may protect against metabolic syndrome." Related nutrients are also important for skin and bone health and can aid in lowering one's blood pressure. 

Goodson says that seaweed is also rich in vitamins C, K and folate, plus minerals such as calcium and magnesium. And it's the best source of dietary iodine, she explains, which plays an important role in supporting thyroid function. "Seaweed is also a good source of dietary fiber," she adds, "which can aid digestion and help with feelings of satiety." 

The U.S. National Ocean Service notes that, due to the plant's anti-inflammatory and anti-microbial agents, seaweed has been used in ancient cultures to treat wounds, burns and rashes, with Egyptians possibly using it as a treatment for breast cancer as well. "Certain seaweeds do, in fact, possess powerful cancer-fighting agents that researchers hope will eventually prove effective in the treatment of malignant tumors and leukemia in people," the agency notes.

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Is it healthy to eat seaweed every day? 

Because of such nutrients and properties, seaweed is a wonderful food to include in one's regular diet. Like all foods, however, it's important to avoid overconsumption and to eat well-balanced meals. 

It's also helpful to keep in mind that, "while the heavy metal content in seaweed is generally very low, consuming very large amounts of seaweed may lead to unhealthy consumption of heavy metals like arsenic and aluminum," cautions Weintraub. She adds that people with certain health conditions such as thyroid disorder are vulnerable to consuming excess iodine, "and may therefore need to limit the amount of seaweed consumed." 

As long as such considerations are kept in mind, Goodson says, "seaweed is highly nutritious and generally safe for consumption."