Restricting feeding to daytime can entrain circadian clocks in peripheral organs of rodents, and nutrients that rapidly increase the blood glucose level are suitable for inducing entrainment. However, dietetic issues, for example, whether or not the diet comprises heated food, have not been fully explored. We therefore hypothesized that rapidly digested starch causes stronger entrainment than slowly digested starch. The entrainment ability of the liver clock in PER2::LUCIFERASE knock-in mice, blood glucose levels, insulin levels, and acute changes in liver clock gene expression were compared between a β-starch (native)-substituted AIN-93M standard diet and an α-starch (gelatinized)-substituted diet. β-Corn and β-rice starch induced larger phase delays of the liver clock, larger blood glucose increases, and higher Per2 gene expression in the liver compared with β-potato starch. Starch granule size, as examined by electron microscopy, was larger for β-potato starch than for β-corn or β-rice starch. After heating, we obtained gelatinized α-potato, α-corn, and α-rice starch, which showed destruction of the crystal structure and a high level of gelatinization. No difference in the increase of blood glucose or insulin levels was observed between β-corn and α-corn starch, or between β-rice and α-rice starch. In contrast, α-potato starch caused higher levels of glucose and insulin compared with β-potato starch. An α-potato starch-substituted diet induced larger phase delays of the liver clock than did β-potato starch. Therefore, rapidly digested starch is appropriate for peripheral clock entrainment. Dietetic issues (heated vs unheated) are important when applying basic mouse data to humans.
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