Kelp goes by many common names, as there are hundreds of species of this alga. Some species have multiple common names. The kelp species Ascophyllum nodosum, for instance, is commonly known as Norwegian kelp, knotted kelp, rockweed, knotted wrack, and egg wrack. In some cases, more than one species share a common name. For example, the kelp species Saccharina japonica and Laminaria digitata are both commonly referred to as kombu.
Kelp thrive in a variety of ocean habitats including dense ocean forest formations, shallow shoreline waters and intertidal zones, and estuaries. Most species require water temperatures of at least 40 degrees Fahrenheit to thrive.
Polysaccharides; minerals; amino acids; proteins; vitamins; pigments.
Kelp is brown algae or seaweed, and there are hundreds of kelp species found in oceans throughout the world. Until recently, it was thought that kelp was found only in temperate or polar waters, but in 2007 kelp forests were discovered in the tropical waters off the Ecuadorian coast.1 Which species are actually kelp and which are not can be a bit confusing, depending on whether the word kelp refers to a biological classification or a cultural designation. Until the 20th century, any type of seaweed that could be burned to make soda ash was considered kelp. This encompassed the species of seaweeds that belong to the orders Laminariales and Fucales. Since then the Fucales order, which includes the genus Ascophyllum, is no longer classified by biologists as kelp – but language and customs continue to treat it as though it is. Even though a marine biologist will not refer to the species Ascophyllum nodosum as kelp, it is still colloquially known as Norwegian kelp and knotted kelp. For the purposes of this writing, we are using the term kelp more broadly.
Kelp plays an essential role in ocean ecology. Large kelp forests provide the habitat for numerous other species. One biologist reports that in Norway’s dense coastal kelp forests, there are over 100,000 sponges, moss animals, sea squirts, and other invertebrates per square meter that live on kelp (Laminaria hyperborean) stems.2 Pollution, overfishing, and climate change all threaten the health of large kelp forests. Other species of kelp, such as Ascophyllum nodosum, provide habitat for fish, ocean invertebrates, and even shore birds.
Commercial interests have depended on kelp, especially kelp ash, since the industrial age began. In the 1700s and into the early 1800s in Scotland, kelp provided the soda ash essential to industry and manufacturing, especially in soap and glass making. Today kelp provides raw materials used in food and product manufacturing; it is also used in fertilizers. China is the world’s largest commercial producer of Saccharina japonica, producing 250,000 tons (dry weight) each year.3 The alginate from some kelp species is used as a thickener in foods and personal care products. Kelp has been used in the cuisines of numerous cultures for millennia. Kombu, or Saccharina japonia, is used in broths, stews, rice dishes, food wraps, and as a flavoring ingredient in Asian cultures. Since at least the Middle Ages, kelp has been a recognized remedy for goiter. (We now know that it is rich in iodine.)
Some varieties of kelp have been extensively studied for their nutrient content, and are especially rich in minerals. The species Ascophyllum nodosum contains almost 3 grams of fiber per serving, along with 26% of the daily reference nutrient intake (RNI) of calcium, 7% of potassium, 24% of magnesium, 54% of iron, 22% of copper, and 4100% of the RNI for iodine.4 It even contains small amounts of polyunsaturated fatty acids in the ideal omega-3 to omega-6 ratio.5 The species Laminaria digitata is equally nutrient-dense, with 3 grams of fiber per serving, along with 176 mg calcium, 976 mg potassium, 195 mg magnesium, 22 mg iron, and 34 mg iodine.6
Different species of kelp contain different bioactive compounds, which researchers are only now beginning to study. Compounds of interest in Ascophyllum nodosum and Laminaria digitata, for example, include alginic acid, fucoidan, laminarin, and mannitol.7 Fucoidan in particular has attracted the attention of researchers. In an in vivo study involving mice, researchers compared extracts of fucoidan from kelp (Laminaria japonica) and Cistanche tubulosa (a desert plant) on inflammation. Both compounds were anti-inflammatory, and researchers determined that they acted in a complementary fashion.8 In an in vivo study, researchers also looked at the effects of two polysaccharides on inflammation. Fucoidan (from kelp) and lentinin (from mushrooms) both suppressed interleukin-8, an inflammatory marker; the two substances used different pathways to inhibit the inflammation.9
Researchers have also looked at the immune-stimulating capabilities of kelp. In an in vivo experiment, they discovered that injecting mice with an extract of Ascophyllum nodosum stimulated the activity of natural killer cells the spleen.10 A bioactive compound, acophyllan, found in this species of kelp shows promise in cancer research. It suppressed the spread of cancer cells and contributed to cancer cell death in vitro.11
Kelp’s potential health benefits extend to the treatment of diabetes. Experiments with rats demonstrate that kelp can lower fasting blood glucose levels and support pancreatic islet cell function.12 Kelp also contains compounds that have antioxidant effects. In a series of in vitro experiments, researchers compared the antioxidant function of two compounds found in different species of kelp. Both ascophyllan (from Ascophyllum nodosum) and fucoidan (found in a number of species of kelp) neutralized hydroxy radicals, but ascophyllan was more effective. Ascophyllan also showed greater effect against superoxide molecules.13
1 http://oceanfocus.org/focus-areas/threatened-habitats/kelp-forests/ , accessed June 22, 2013.
2 Christie, H., et al. Species distribution and habitat exploitation of fauna associated with kelp (Laminaria hyperborea) along the Norwegian coast. Journal of Marine Biological Association U.K. 2003. 83, 687-699.
3 http://www.seaweed.ie/aquaculture/kelp_china.php , accessed June 22, 2013.
4 MacArtain, P., et al. Nutritional value of edible seaweeds. Nutrition Reviews. 2007. 65 (12), 535-543.
5 van Ginneken, V., et al. Polyunsaturated fatty acids in various macroalgal species from north Atlantic and tropical seas. Lipids in Health and Disease. 2011. 10 (104).
6 MacArtain, P., et al. Nutritional value of edible seaweeds. Nutrition Reviews. 2007. 65 (12), 535-543.
7 MacArtain, P., et al. Nutritional value of edible seaweeds. Nutrition Reviews. 2007. 65 (12), 535-543.
8 Kyung, J., et al. Synergistic anti-inflammatory effects of Laminaria japonica and Cistanche tubulosa extract. Laboratory Animal Research. 2012. 28 (2), 91-97.
9 Mizuno, M., et al. Different suppressive effects of fucoidan and lentinan on IL-8 mRNA expression in in vitro gut inflammation. Bioscience, Biotechnology, and Biochemistry. 2009. 73 (10), 2324-2325.
10 Nakano, K., et al. Immunostimulatory activities of the sulfated polysaccharide ascophyllan from Ascophyllum nodosum in in vivo and in vitro systems. Bioscience, Biotechnology, and Biochemistry. 2012. 76 (8), 1573-1576.
11 Nakayasu, S., et al. Biological activities of fucuse-containing polysaccharide ascophyllan isolated from the brown alga Ascophyllum nodosum. Bioscience, Biotechnology, and Biochemistry. 2009. 73 (4), 961-964.
12 Long, S.H., et al. The hypoglycemic effect of the kelp on diabetes mellitusmodel induced by alloxan in rats. International Journal of Molecular Sciences. 2012. 13, 3354-3365.
13 Abu, R., et al. In vitro antioxidant activities of sulfated polysaccharide ascophyllan isolated from Ascophyllum nodosum. International Journal of Biological Macromolecules. 2013. http://dx.doi.org/10.1016/j.ijbiomac.2013.04.035
1. Biological activities of fucuse-containing polysaccharide ascophyllan isolated from the brown alga Ascophyllum nodosum
Nakayasu, S., et al. Bioscience, Biotechnology, and Biochemistry. 2009. 73 (4), 961-964.
Researchers isolated ascophyllum, a component of Ascophyllum nodosum (kelp), to examine its effects against lymphoma (cancer) cells in vitro. The ascophyllan suppressed the spread of the cancer cells in a dose dependent manner. Researchers also observed changes consistent with cell death, such as structural changes in the cell nucleus and DNA fragmentation. In a second experiment, researchers exposed rodent leukemia cells to ascophyllan. This stimulated the activity of tumor necrosis factor alpha, a signaling molecule involved in immune function. Researchers conclude that ascophyllan from kelp may have beneficial anti-tumor effects.
2. Dietary Ascophyllum nodosum increases urinary excretion of tricarboxylic acid cycle intermediates in male Sprague-Dawley rats
Simmons-Boyce, J.L., et al. The Journal of Nutrition. 2009. 139, 1487-1494.
In this animal study, researchers looked at the safety and physiological effects of Ascophyllum nodosum (kelp). Rats were divided into four groups and fed a control diet, or a diet containing 5, 10, or 15% kelp. A variety of blood and urinary markers were measured throughout the experiment. While the rats did excrete more TCA-cycle intermediates than normal, there were no harmful side effects identified in liver or kidney function even when kelp was administered at 15%. Researchers conclude that these findings will be helpful in future seaweed studies.
3. Immunostimulatory activities of the sulfated polysaccharide ascophyllan from Ascophyllum nodosum in in vivo and in vitro systems
Nakano, K., et al. Bioscience, Biotechnology, and Biochemistry. 2012. 76 (8), 1573-1576.
Researchers looked at the effects of ascophyllan, a component of Ascophyllum nodosum (kelp), on immune cell activity in mice. In this in vivo experiment, researchers injected ascophyllan into the abdominal cavities of mice. As a result, the natural killer cells of the spleen demonstrated more activity against lymphoma cells. In vitro experiments did not show as much clear benefit. When test results are taken as a whole, researchers conclude that ascophyllan is a powerful immune booster because it stimulates natural killer and macrophage defenses.
4. The hypoglycemic effect of the kelp on diabetes mellitus model induced by alloxan in rats
Long, S.H., et al. International Journal of Molecular Sciences. 2012. 13, 3354-3365.
In this rat study, researchers investigated the effects of kelp on blood sugar and insulin levels. Diabetes was induced in rats and they were given kelp as part of their diet. Compared to a control group, the diabetic rats given kelp had higher insulin levels and lower fasting blood glucose levels. The rats’ pancreatic islet cells (which produce insulin) also showed improvement. Researchers conclude that kelp may act as an antioxidant to help lower fasting blood sugar and may support islet cell function.
5. In vitro antioxidant activities of sulfated polysaccharide ascophyllan isolated from Ascophyllum nodosum
Abu, R., et al. International Journal of Biological Macromolecules. 2013. http://dx.doi.org/10.1016/j.ijbiomac.2013.04.035
In a series of in vitro experiments, researchers looked at the antioxidant effects of ascophyllan, a polysaccharide found in kelp, compared to fucoidan, another polysaccharide found in kelp and other species of seaweed. Researchers demonstrated that ascophyllan has a greater antioxidant effect on superoxide molecules than fucoidan. Both of these polysaccharides also exerted antioxidant activity against hydroxy radicals, but ascophyllan was more effective.
6. Polyunsaturated fatty acids in various macroalgal species from north Atlantic and tropical seas
van Ginneken, V., et al. Lipids in Health and Disease. 2011. 10 (104).
Polyunsaturated fatty acids (PUFA) have long been associated with cardiovascular health, mental health, and anti-inflammatory activity. In this study, researchers evaulated the PUFA content of seven varieties of seaweed, including Ascophyllum nodosum (kelp). Omega-3 and omega-6 fatty acids were identified, ranging from 2 to 14 mg/g of dry matter. Total fat content was between 7 and 45 mg/g of dry matter. In terms of total fatty acids, the seaweed varieties were made up of 8 to 63% omega 3 fats, 3 to 32% omega 6 fats, and 3 to 56% omega-9 fats. Both red and brown seaweeds (including kelp) contain arachidonic and eicosapentaenoic (EPA) acids. Researchers conclude that seaweeds such as these are a renewable source of PUFAs, and contain a healthy 1:1 ratio of omega-6 to omega-3 fatty acids.
7. Synergistic anti-inflammatory effects of Laminaria japonica fucoidan and Cistanche tubulosa extract
Kyung, J., et al. Laboratory Animal Research. 2012. 28 (2), 91-97.
Researchers administered extracts of fucoidan (from Laminaria japonica, a species of kelp) and Cistanche tubulosa (a desert plant) and simultaneously induced inflammation in mice. The treatments continued for a series of days; then the tissues of the mice were examined. Both the kelp and the Cistanche tubulosa demonstrated anti-inflammatory effects. Researchers noted two complementary effects; the fucoidan from kelp inhibited the infiltration of inflammatory cells, while the Cistanche tubulosa suppressed the activity of the inflammatory cells. Researchers believe that together these extracts could have applications in treatments for anti-inflammatory conditions.
8. Different suppressive effects of fucoidan and lentinan on IL-8 mRNA expression in in vitro gut inflammation
Mizuno, M., et al. Bioscience, Biotechnology, and Biochemistry. 2009. 73 (10), 2324-2325.
In this experiment, researchers used an in vitro model for gut inflammation that deliberately stimulated production of interleukin-8, a component of the body’s immune defenses. They then looked at the anti-inflammatory effects of two polysaccharides: fucoidan from kelp and lentinan from mushrooms. Both substances suppressed interleukin-8, using different pathways.
9. Nutritional value of edible seaweeds
MacArtain, P., et al. Nutrition Reviews. 2007. 65 (12), 535-543.
A recent study analyzed eight different varieties of seaweed, including kelp (Ascophyllum nodosum), for nutrient content. In the context of daily reference nutrient intakes (RNI), researchers measured the nutrients in one 8-gram serving. A serving of kelp contains 2.8 grams of fiber, approximately 11% of the RNI. It contains 184 mg of calcium (26% of RNI), 245 mg potassium (7%), 72 mg magnesium (24%), 375 mg sodium (23%), 0.3 mg copper (22%), 4.7 mg iron (54%), and 5.8 mg iodine (4100%). Kelp is also a rich source of vitamin B9, providing 390% of the RNI. Trace amounts of other vitamins are also present. Kelp also contains compounds which are believed to have bioactive properties; the compounds include alginic acid, fucoidan, laminarin, and mannitol.