Updated on October 13, 2021

Medically reviewed by Melissa Rifkin, MS, RD, CDN

Kelp (Laminaria) is a type of brown seaweed that usually grows in large underwater forests. While seaweed can grow in nearly any type of saltwater or freshwater, kelp is found only in saltwater, typically along nutrient-rich, cold, rocky coastlines. There are about 30 different varieties of kelp. Kelp provides nutrition for a wide range of sea life. People also consume this leafy seaweed, because of its high nutritional value.

Kelp—along with other types of edible seaweed—has been a staple in the Japanese diet for hundreds of years. Now this food has become common in other parts of the world, due in part to the popularity of kelp noodles.

Kelp Nutrition Facts

The following nutrition information is provided by the USDA for 1 cup (15g) of dried seaweed.1

• Calories: 44.7
• Fat: 0.6g
• Sodium: 86.2mg
• Carbohydrates: 7.9g
• Fiber: 0.8g
• Sugars: 0.5g
• Protein: 4.8g

Carbs

The carbohydrate content of dried kelp is low, with under 8 grams in a full cup. Of this, under 1 gram comes from sugar and fiber.

Fats

There is very little fat naturally found in kelp although it may be added during cooking.

Protein

Dried kelp has almost 5 grams of protein per cup.

Vitamins and Minerals

Kelp contains many important vitamins and minerals, including vitamins K, A, C, and E in addition to folate, vitamin B12, and vitamin B6. It also provides small amounts of thiamin, riboflavin, niacin, and pantothenic acid.

Iodine is a mineral that's present in high amounts in kelp. Other minerals include calcium, magnesium, iron, sodium, and phosphorus.

Health Benefits

Kelp is high in nutritional value because it's very low in calories but packed with fiber, vitamins, and minerals, which offer various health benefits:

• Vitamin C: An antioxidant that may help prevent illness or disease
• Calcium: Aids in bone health
• Iron: Important for healthy blood and disease resistance
• Magnesium: Essential for hundreds of biochemical reactions in your body
• Iodine: Necessary for the production of thyroid hormones and to maintain a healthy metabolism

Promotes Weight Loss

Some research has suggested that the type of fiber found in seaweed, including kelp, may help with satiety and feeling of fullness, which may help people consume fewer overall calories. Seaweed itself is low in calories and fat, and one of the antioxidants found in seafood, called fucoxanthin, may also help with weight loss.2

Lowers Cancer Risk

While more research is needed, three compounds found in seaweed have shown some preliminary promise in fighting cancer:

• Fucoidan, a type of fiber found in seaweed
• Polyunsaturated fatty acids
• Polyphenols (antioxidants)2

Lowers High Blood Pressure

Some of those same compounds, such as fucoidan and fucoxanthin, may also help people who have high blood pressure. Folate, as well, has been shown to help maintain healthy blood pressure, and seaweed can be a good source of this B vitamin.3

Allergies

Allergy to kelp or other seaweed is rare, but possible.4 If you experience symptoms of food allergy after eating kelp (such as swelling or rash, especially around the mouth), consult a doctor.

Adverse Effects

Kelp is likely safe when consumed in the amounts typically found in food. However, the high amount of iodine and potentially heavy metals in kelp can be detrimental to your health if you consume too much, especially in the form of supplements.2

Your recommended daily intake of iodine depends on your age and sex. Most adults need 150 micrograms per day. The upper limit (the most that should be consumed in a day) is 1,100 micrograms.

Since the iodine content in kelp and kelp products varies, it can be unclear how much iodine you will consume when you eat it. Consuming too much iodine can cause serious negative health effects, such as goiter, thyroid gland inflammation, and, in severe cases, thyroid cancer. Exposure to heavy metals can also harm thyroid function.5

For these reasons, health experts advise that pregnant or breastfeeding women and those with kidney or thyroid disorders, such as hyperthyroidism, avoid consuming kelp.2

Varieties

There are different varieties of kelp, one of which is kombu. Kombu is the Japanese word for kelp, usually the Saccharina japonica species.

Raw and dried kelp and kelp noodles are found in many specialty markets. Kelp noodles can also be found in some grocery stores and supermarkets in the Asian food section. You can also buy kelp and kelp noodles online.

Note that the nutrition of kelp noodles will vary based on the product that you buy and the recipe you use. Brands with just kelp, water, and sodium alginate (a natural hydration agent that is extracted from brown seaweed) will be low in calories, carbs, and fat while still offering some of the nutritional benefits of plain kelp.

Storage and Food Safety

Dried kelp and kelp noodles are usually packaged so that you can keep them in your cupboard for about six months, as long as they are unopened. You can keep fresh or rehydrated kelp in the refrigerator for a few days.

How to Prepare

Raw kelp can be used in stir-fry dishes and soups, added to salads, or included in smoothies. Dried kelp can be added to the pot when cooking dried beans to enhance flavor and make them less gas-causing. It can also be used to add flavor to soups and broths.

Kelp noodles can be consumed cold or heated, but you should rinse the noodles before consuming. Try adding them to green salads, using them as a pasta alternative, or tossing with sauteed veggies and a protein.