The alginates in kelp (complex polysaccharides), like other soluble fibers, have a soothing and cleansing effect on the digestive tract and are known to prevent the absorption of toxic metals like mercury, cadmium, plutonium and cesium. Studies have shown that alginate supplements can reduce strontium-90 absorption from the intestinal tract by as much as 83%.

The U.S. Atomic Energy Commission advocates 2 tablespoons of alginate supplement per day to prevent strontium-90 absorption and related issues. Kelp alginates are also hydrasorbent laxatives, compounds that swell to 20 times their original volume by absorbing water, which is much greater than other types of bulk laxatives such as psyllium and bran. Kelp alginates are effective in treating habitual constipation and gastric bloating because they swell in intestinal juices rather than water or gastric juices and are non-irritating.

Several studies also document a direct, stimulatory effect of seaweed on the immune system. Kelp has been shown to inhibit 95% of abnormal cell growths, and cause regressions in 6 out of 9 animals tested. In-vitro studies of hot water extract of Laminaria on abnormally growing human cells showed more than 50% apoptosis. Kelp also has antiviral activity against influenza virus due to a very active inhibitor of viral and bacterial neuraminidase.