The effects of diurnal intermittent fasting on the wake-promoting neurotransmitter orexin-A

Abstract

Background: Food restriction has been demonstrated to increase the alertness in different species and to increase the levels of the wake-promoting neurotransmitter orexin. We hypothesized that diurnal intermittent fasting (DIF) increases orexin-A levels during fasting. Therefore, we conducted this study to assess the effects of DIF, during the month of Ramadan, on orexin, while controlling for lifestyle changes that may accompany Ramadan such as sleep duration, bedtime and wake time, energy expenditure, light exposure, and food.

Methods: Eight young healthy volunteers (mean age, 25.4 ± 3.5 years) reported to the laboratory on three occasions: (1) 4 weeks before Ramadan while performing DIF for 1 week outside the month of Ramadan (fasting outside Ramadan); (2) 1 week before Ramadan (nonfasting baseline) (BL); and (3) during the 2^nd week of Ramadan while performing DIF (Ramadan). Plasma levels of orexin-A were measured using an enzyme immunoassay five times at 22:00, 02:00, 04:00, 06:00, and 11:00. Caloric intake, light exposure, and sleep schedule were maintained during the participants' stays in the laboratory in the three study periods.

Results: Orexin-A levels increased in the daytime during fasting and decreased at night compared to BL. The differences in orexin-A levels between DIF and BL were significant at 06:00, 11:00, 22:00, and 02:00.

Conclusions: DIF increases orexin-A levels in the plasma during fasting hours. This finding supports findings from animal studies showing that fasting increases alertness.

Keywords: Hypocretin; Ramadan; intermittent fasting; orexin; sleep; vigilance.

Figure 1

Study protocol

Figure 2

Circadian pattern of plasma orexin-A concentrations in eight healthy male volunteers before and during Ramadan daytime fasting. Each point represents the mean and standard deviation of the eight subjects. Values at baseline (…♦…) (red line), baseline fasting before Ramadan (---◾---) (blue line), and Ramadan (-▴-) (green line) are presented. The dark-headed arrows indicate the approximate meal time during fasting (Ramadan and fasting outside Ramadan), and the white-headed arrows indicate the meal time during baseline. (◻) indicates wakefulness and (◼) indicates sleep. *The difference between both Ramadan and fasting outside of Ramadan and baseline measurements is significant (P < 0.05). **The difference between fasting outside Ramadan and baseline is significant (P < 0.05)