Kombu is a brown seaweed from the Laminaria genus. People use it dried or powdered as a dietary supplement. East Asian cuisines rely on it for umami flavor and for supplying iodine and other minerals.
The seaweed delivers soluble fiber in the form of alginates, which helps smooth digestion. Its iodine supports normal thyroid function. Mineral levels in kombu can swing widely from batch to batch.
Dried kombu concentrates its iodine a lot. Going overboard can mean excessive iodine intake. Anyone with a thyroid condition or on thyroid medication should use it sparingly.