What to Know About Sea Vegetables

Medically Reviewed by Poonam Sachdev on November 24, 2022
6 min read

If you’re looking for a tasty addition to your diet that’s packed with essential nutrients, you should give sea vegetables a try. The term “sea vegetable” is used to describe all varieties of edible seaweed. You can find this product at most grocery stores in the form of dried sheets or flakes and as an ingredient in other products. 

No single dietary change can transform your health. But, of all the so-called superfoods available, sea vegetables are a true nutritional powerhouse.

Sea vegetables — or seaweed — are all different types of algae. Algae grow in marine environments. They use sunlight for energy and naturally absorb vitamins and minerals from the ocean. 

Many Americans are unfamiliar with the concept of sea vegetables, but they’ve been widely used throughout Asia and other areas of the world for countless generations. Some of the countries where sea vegetables are a popular dietary ingredient include: 

  • Japan
  • Korea
  • China
  • Philippines
  • Parts of the U.K.

There are over 30 edible species of algae on the market today. They're broadly classified into the three categories of red, green, and brown algae. The most common varieties often go by multiple names. In the U.S., Japanese names are often used. 

Each species has a unique form, texture, taste, and nutrient composition. Common varieties of algae are described in the edible sea vegetables list below: 

  • Nori. This is the mildest-tasting seaweed. It’s commonly used as the green wrapping on the outside of sushi rolls. It’s rich in healthy omega-3 fatty acids and has less iodine than other varieties.  
  • Kelp. This is a general term that applies to a few different types of seaweed, some of which are discussed below. Kelp is eaten more than any other algae variety. 
  • Kombu. This is a type of brown kelp. It makes a hearty flavoring in soups. It’s also used in products as diverse as toothpaste and fertilizer. 
  • Arame. This is another type of brown kelp. It has a vaguely sweet taste and a firmer texture than other varieties. 
  • Dulse. This is a type of red algae that grows in the northern Atlantic and Pacific oceans. It has a softer, chewier texture than other types of algae. It has high levels of protein. It’s also used as an ingredient in beauty products. 
  • Carrageenan. This is also known as Irish moss. It’s often used in vegetarian foods as a gelatin substitute. 

You can purchase many of these varieties in a wide array of forms, including: 

  • Dried sheets
  • Snack packs
  • Flakes
  • Noodles
  • Pills

Japan is the main producer and exporter of sea vegetables. Most of the U.S. supply comes from Japan. Seaweed is both grown on commercial farms and harvested from wild areas. 

Before buying any seaweed products, you need to make sure that they come from a trusted source. Along with all of the nutritious vitamins and minerals, algae also absorb dangerous heavy metals from their marine environments. This means that all naturally harvested seaweed needs to come from a clean area in the ocean. 

These heavy metals include arsenic, lead, and cadmium. Arsenic is likely the most prevalent contaminant in the available seaweed supply. 

The U.S. Department of Food and Agriculture (USDA) regulates edible seaweed products. Look for its seal on the packaging to ensure that the food doesn’t contain dangerous contaminants. USDA organic certified products are also specifically tested for heavy metal contaminants before they’re sold to the public.

There are countless nutrients found in all varieties of sea vegetables. Many of these are considered essential nutrients and some are exceptionally good for your health. 

The exact nutrient balance can depend on things like the exact species, the area where the seaweed was harvested, and the timing of harvest. In some situations, plant protein can make up 47% of the dry weight of certain species — which is great for vegetarian diets. 

Additional examples of sea vegetables' nutritional ingredients — both dried and raw — include: 

Adding seaweed to your diet is a simple way to pack a lot of necessary nutrients into a small package. Its wide array of beneficial ingredients means that all varieties of seaweed can improve your health. 

Examples of sea vegetable health benefits include: 

  • Help with weight loss. The low caloric and fat content make seaweed great for almost any diet. It also contains a polysaccharide called alginate, which has been shown to limit fat production.  
  • The ability to lower your blood pressure. A meta-analysis of 100 studies on algae found that consuming seaweed on a regular basis can lower your blood pressure. 
  • Help with heart health. The same meta-analysis of 100 studies also found that seaweed consumption has a positive effect on overall heart health and could lower your risk of certain heart conditions. 
  • Anti-inflammatory and antiviral properties. These properties are attributed to the presence of beneficial compounds called phytonutrients — like sulfated polysaccharides. 
  • Cancer prevention. Early research indicates that folic acid, which is present in most seaweed varieties, may help lower your risk of colon cancer and estrogen-related cancers, like breast cancer.

Even though it’s full of beneficial ingredients, eating seaweed isn’t good for everyone. You should avoid eating large amounts of all types of sea vegetables if you have certain health problems, take specific medications, or follow particular dietary restrictions. This includes people who:  

  • Take the blood thinning medication warfarin. The large amounts of vitamin K found in most algae can interfere with this medication's ability to prevent blood clots.
  • Have kidney problems. The amount of potassium in just 2 tablespoons of seaweed is 35 times greater than that in a banana — one of the most famous potassium-containing foods. These high levels are fine for healthy people but can harm those with kidney problems. 
  • Have thyroid problems. Even small amounts of seaweed have iodine levels that dramatically exceed your daily recommended allowance. Although recommended amounts of iodine can actually benefit your thyroid health, getting too much may induce hypothyroidism. 
  • Are on a low-sodium diet. Seaweed absorbs lots of salt from the ocean. Sodium is one of the two molecules that make up table salt. So, if you’re avoiding sodium, it’s best to avoid seaweed too.

Seaweed is normally sold in dried sheets. In most cases, you’ll want to rehydrate it before you eat it. You can do this by adding it in dry to the food that you’re cooking. Just make sure that the dish is wet enough to adequately rehydrate the sea vegetable. Soup is a great example of this type of dish. Cut the seaweed up into strips before adding it to your miso soup.  

Otherwise, you can rehydrate the sheets by briefly soaking them in water. Simply dip the sheets into a bowl of water and let them absorb water until they reach your desired texture. Luckily, this isn’t a time-consuming process. 

Many Americans are most familiar with seaweed's use as a wrap for sushi rolls. But you can add seaweed to any number of dishes — from casseroles to baked goods. 

Keep granulated or flaked forms of kelp around as a fantastic salt substitute. You can even try preparing a dish with a product called kelp noodles. They don’t require cooking and are both sugar- and fat-free. 

Some people eat seaweed raw. For example, in Japanese and Korean cuisine, fresh, raw arame is tossed with sesame oil and served with lettuce. 

There are so many different ways to eat seaweed that almost anyone can find a dish that they enjoy. If you don’t like the first kind that you try, be creative and give it another go. The health benefits could be significant.