Figure 2.
A 5-hr Delay in Meal Times Delays the Plasma Glucose Circadian Rhythm
(A–C) Concentration of glucose (A), insulin (B), and triglyceride (C) in 2-hourly plasma samples collected in constant routine conditions. Data are plotted as mean ± SEM. Black circles with solid lines represent data following early meals (0.5, 5.5, and 10.5 hr after waking up). White squares with dashed lines represent data following a 5-hr delay in each meal.
(A) There were significant effects of time (F(14,126) = 3.71, p < 0.001), meals (F(1, 9) = 29.84, p < 0.001), and meal × time interaction (F(14,126) = 5.10, p < 0.001) on glucose concentration.
(B) There was a significant effect of time (F(14,126) = 2.79, p = 0.001), but no significant effect of meals (F(1, 9) = 4.69, p = 0.059) or meal × time interaction (F(14,126) = 1.16, p = 0.312) on plasma insulin concentration.
(C) There was a significant effect of time (F(14,126) = 18.44, p < 0.001), but no significant effect of meals (F(1, 9) = 0.01, p = 0.913) or meal × time interaction (F(14,126) = 1.19, p = 0.294) on plasma triglyceride concentration.
(D–F) Acrophase of glucose (D), insulin (E), and triglyceride (F) rhythms in individuals following early meals (constant routine 1, CR1; black circles) and following a 5-hr delay in meal time (constant routine 2, CR2; white squares). Using a paired t test, there was a significant effect of meal timing on glucose phase (delay of 5.59 ± 1.29 hr; t(9) = 4.415, p < 0.001), but not on the phase of insulin (t(9) = 2.179, p = 0.029; note Bonferroni-corrected critical p value below) or triglyceride (t(9) = 0.896, p = 0.197).
(A–F) Data are from n = 10 participants, calculated relative to each individual’s dim light melatonin onset (DLMO). Statistical significance is defined as p < 0.01 (following Bonferroni correction for analysis of a total of five rhythmic plasma markers).