Figure 3
Time course of energy metabolism in two age groups of 10 years apart. (a–d) Fifty-three men were grouped as younger (n = 27, under 25 years of age) or older (n = 26, 25 years or more)9,19,20,21,22. Subjects took breakfast (7:00, 8:00 or 9:00), lunch (12:00, 12:30 or 13:00), and dinner (18:00), and slept for 7 or 8 h from 23:00 (grey bars). Because of unequal duration of sleeping period, the 8th hour of sleep in one experiment was not included for statistical analysis9. Mean ± SE of RQ, energy expenditure, carbohydrate oxidation and fat oxidation for 23 h common to all data sets were shown for younger (black lines) and older (grey lines) group. A linear mixed-models ANOVA showed a significant effect of time (P < 0.01) and a group × time interaction (P = 0.032), but main effect of group was not significant (P = 0.078) for RQ. Similarly for carbohydrate oxidation, significant effect of time (P < 0.01) and a group × time interaction (P = 0.043) were found, but main effect of group was not significant (P = 0.792). For energy expenditure and fat oxidation, main effect of time was significant (P < 0.01), but main effect of group (P = 0.066 for energy expenditure and P = 0.129 for fat oxidation) and group × time interaction was not significant (P = 0.376 and P = 0.290). *Represents significant difference between the 2 subgroups by post hoc pair-wise comparisons (P < 0.05). Significant difference in RQ in the morning requires cautious interpretation, since % of subjects who took breakfast before 9:00 was not matched; 52% in younger and 69% in older group, respectively. (e–h) Absolute difference between two age groups were plotted against mean of the two subgroups for RQ, energy expenditure, carbohydrate oxidation and fat oxidation. Values during sleep were shown as filled symbols (filled blue circles). Significant negative correlation between absolute difference and mean of the two subgroups was observed in RQ (P < 0.001).
