The Nutritional Value Of Seaweed

Seaweeds comprise a significant food source in the cuisines of coastal cultures around the world. They also are attributed with a variety of health-promoting properties, including antibacterial, antiviral, antioxidant and anti-inflammatory activity. Some of the purported nutritional and health benefits of seaweed have been studied in recent scientific research.

Minerals

Seaweed is a remarkably rich source of minerals which it extracts from the sea water it grows in. Seaweed contains most of the major as well as minor minerals required for good health, including sodium, calcium, magnesium, potassium, chlorine, sulfur, phosphorus, iodine, iron, zinc, copper, selenium, molybdenum, fluoride, manganese, boron, nickel and cobalt.

Known for its high iodine content, a single gram of brown algae -- which contains the highest iodine content among seaweed varieties -- has as much as 53 times the 150 mcg daily requirement, while nori, the variety commonly used to prepare sushi, contains about 100 to 300 mcg per gram. Seaweed is also among the richest plant-derived sources of calcium, at 70 mg per gram.

Protein

Seaweed varieties vary considerably in protein content. Brown algae, which tops the list for iodine, contains the lowest protein values at 5 to 11 percent. Green algae offers a slightly higher 20 percent, but is not commonly harvested for commercial purposes. Red algae, at 30 to 40 percent, is on par with the protein content of legumes, and spirulina -- a type of blue-green algae -- provides a whopping 62 percent protein, according to the University of Maryland Medical Center.

Thyroid Function

Seaweed had a suppressive effect on thyroid function, as reported in a study published in the 2008 "Endocrinology Journal." Kombu, a popular form of seaweed in Japanese cuisine, at 15 g and 30 g per day for seven to 10 days increased levels of thyroid stimulating hormone, surpassing the upper limits of normal for some study participants. Between 55 to 87 days of 15 g per day, thyroid stimulating hormone levels remained elevated while free thyroid hormone levels were unaffected, indicating a suppression of thyroid function. Additionally, kombu ingestion caused significant excretion of iodine. These out-of-normal-range values returned to normal limits within 40 days of discontinuing kombu; however, the researchers advise that excessive consumption of kombu be avoided.

Prebiotics

Prebiotics are compounds that function as food sources for beneficial bacteria in the intestinal tract. These substances, often polysaccharrides, are present in seaweeds and may potentially be extracted from seaweeds and marketed as a supplement, according to a study published in the 2010 "Marine Drugs." Introduction of seaweed extract into the diets of farm animals resulted in increased levels of the beneficial Lactobacillus bacteria and lower numbers of harmful E. coli bacteria in the intestines of farm animals. These results offer implications for higher food safety and also for the possibility of a similar effect of raising the levels of good bacteria in the digestive tracts of humans who consume seaweed or seaweed polysaccharide extracts.

Contamination

Some controversy exists over the potential for seaweed to carry elevated levels of toxic metals that may be present due to pollution or high natural occurrences in surrounding waters where the seaweed is harvested. A study in the 2007 "Environmental Health Perspectives" refuted a previous study in the same publication. It reported toxic levels of arsenic in a sampling of herbal kelp supplements, citing that the authors failed to include key values required to calculate concentration levels. These values, namely the size of a capsule or average dose, when calculated at levels even one-tenth a commonly available capsule size, put arsenic levels well within the safety levels referred to by the authors themselves. This report emphasizes the high safety standards that exist and to which the supplement industry adheres.