Researchers studied the effect of traditional Japanese breakfast foods on insulin sensitivity in a small sample of individuals with impaired glucose tolerance. The group which ate foods such as natto (fermented soybeans) and viscous vegetables (such as Japanese yams and okra) for 2 weeks demonstrated improved insulin sensitivity, serum lipids, and oxidative stress compared to the control group.
British Journal of Nutrition. 2012 Apr;107(8):1184-1191. (Taniguchi-Fukatsu et al.)