Circadian Clocks, Food Intake, and Metabolism - Progress in Molecular Biology and Translational Science - page 121

arrhythmicity) can be induced by complete suprachiasmatic destruction. Of
note, mice rendered arrhythmic by suprachiasmatic lesions display hepatic
insulin resistance. 140 The consequences of circadian misalignment between
the endogenous clockwork and the sleep-wake and feeding-fasting cycles
have been studied in humans, using a protocol of forced desynchrony.
For that purpose, healthy subjects were exposed to seven recurring 28-h
sleep-wake cycles in dim light; this paradigm triggered metabolic alterations
in postprandial glucose responses evoking a prediabetic state. 141
Mealtime being an efficient time giver for peripheral clocks, unusual
times of meals in individuals exposed to a light-dark cycle will induce a state
of internal desynchronization, the master clock being synchronized by light,
while peripheral timing being phase adjusted by feeding times. Thus, it is
consistent to find marked chronobiological effects when, regardless of the
cause, food intake occurs at unusual hours compared to the normal cycle
of sleep-wake cycle. In nocturnal rodents, the metabolic impact of eating
chow pellets only during daytime is weak, as in most case, food-restricted
rodents do not change their body mass. Different conclusions can be drawn
in obese rodents (see below). In them, the spontaneous intake in late after-
noon (end of resting period) seems to have the most detrimental effects on
energy balance. In humans, the critical period is rather at the beginning of
the resting period (early night). Large intake of calories for dinner is associ-
ated with increased body mass index. 142 Another study performed in the
same girls between childhood and adolescence found that larger energy
intake in evening/night meal of children was positively correlated with body
mass index few years later. 143 It should be also noted that patients with night
eating syndrome have a higher risk of developing obesity. 144 Whether the
discrepancies in consequences of meal timing between rodents and humans
rely on interspecies or nocturnal-diurnal differences remain to be
established. Finally, in shift workers, a high intake at lunch has been iden-
tified as a particularly deleterious factor (i.e., it increases the risk of develop-
ing a cardiometabolic syndrome). Of note, besides the more fractionated
pattern of energy intake, shift workers ingest usually more (

þ

10%) saturated

lipids than regular day workers. 134
Sleep restriction in rats kept in a regular light-dark cycle alters glucose
homeostasis (i.e., hyperglycemia and impaired glucose tolerance), while
leading to body mass loss without significant change in energy intake. 145
In mice, repeated sleep deprivation during early daytime leads to some met-
abolic disruption, such as impaired gluconeogenesis. 146 In humans, sleep
curtailment is increasing worldwide. Chronic partial sleep deprivation has