Effects of Daily Kombu (Laminaria japonica) Intake on Body Composition, Blood Pressure, and Fecal Microbiota in Healthy Adult Japanese: A Randomized, Double-Blind Study.

Visceral obesity is considered to have a significant role in the development of metabolic syndrome; therefore, a diet that suppresses visceral fat accumulation could prevent its onset. The effects of kombu consumption on reducing body fat and associated changes in gut microbiota were assessed in a randomized, double-blind, placebo-controlled intervention study in Japanese adults. Random assignment of study subjects between two groups was performed, and over 12 weeks the test group consumed cookies containing boiled kombu powder, while the placebo group consumed cookies containing cellulose. Anthropometric profiles for each participant, including visceral fat area (VFA), were recorded at weeks 0, 6, and 12. Body fat content and percentage were significantly decreased in the male kombu group compared to the placebo group. Systolic blood pressure was significantly lower in males and females in the kombu group compared with the placebo group. Serum adiponectin levels in males were significantly higher in the kombu group compared with the placebo group. The concentration of serum thyroid hormones did not increase after 420 μg/day of iodine consumption throughout kombu intake. Significant increases in the abundances of genus Faecalibacterium, Bacteroides, Alistipes, and Agathobacter were observed in the kombu group compared to the placebo group. Changes in body fat content and percentage were significantly negatively correlated with the relative abundance of Agathobacter in men. The consumption of kombu powder, which is high in alginate, may help prevent body fat accumulation in male subjects and improve microbiota in both males and females.