Various seaweeds have traditionally been used as flavoring materials, food additives, and foodstuffs in many countries, especially those in Asia. The seaweed Laminaria japonica (LJ) is popular as "kombu" in Japanese cuisine. Laminaria sp. is one of the most important marine medicinal foodstuffs, as its biological functions have been widely investigated in both in vitro and in vivo experiments. This chapter introduces recent reports on the ability of Laminaria to prevent obesity and diabetes, and some approaches for effectively using the bioactivities found in Laminaria. The inhibitory effects of Laminaria sp. on triglyceride absorption were investigated in triglyceride-loaded mice and in mice with high-fat-diet-induced obesity. Shaved Laminaria, known as "tororokombu," showed more effective activities in these experiments. The active component was considered to be alginic acid in the water-soluble fraction. On the other hand, the antihyperglycemic effects of a hot water extract of immature Laminaria were investigated in carbohydrate-loaded mice and in in vitro experiments using Caco-2 cells. The potential usefulness of Laminaria sp. as marine medicinal foods may be increased through the use of different processing methods and/or growth stages. These reports suggest that LJ may be useful for preventing lifestyle-related diseases.
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