The second-meal effect of Undaria pinnatifida sporophylls (mekabu) in healthy young women: An open-label crossover study

Abstract

Background: Postprandial hyperglycemia is an early indicator of impaired glucose tolerance and an established risk factor for the development of type 2 diabetes mellitus (T2DM). While low–glycemic index (GI) foods and soluble dietary fibers have shown efficacy in modulating postprandial glycemia, their capacity to influence glycemic responses to subsequent meals—referred to as the "second-meal effect"—remains underutilized in dietary interventions.

Objective: This study aimed to investigate whether breakfast consumption of Undaria pinnatifida (mekabu), a seaweed rich in soluble fiber and sulfated polysaccharides, could attenuate postprandial glycemic response at a subsequent meal in healthy young women.

Methods: An open-label, two-period, crossover study was conducted among healthy female participants. Subjects consumed a test breakfast with or without mekabu, followed by a standardized lunch. Capillary blood glucose levels were measured at multiple time points post-lunch to assess second-meal glycemic modulation.

Results: The findings indicated that mekabu consumption at breakfast significantly reduced postprandial blood glucose levels after lunch, compared to the control condition. These effects may be mediated, at least in part, through delayed gastric emptying and enhanced GLP-1 secretion.

Conclusion: Breakfast intake of mekabu may enhance glycemic stability over successive meals by eliciting a second-meal effect. These findings support the potential utility of mekabu as a functional dietary intervention for the early prevention of T2DM.

Keywords: Mekabu (Undaria pinnatifida), Second-meal effect, Soluble dietary fiber, Postprandial glycemia, Glucagon-like peptide-1 (GLP-1), functional foods, bioactive compounds