The effect of a two-week ketogenic diet, versus a carbohydrate-based diet, on cognitive performance, mood and subjective sleepiness during 36 hours of extended wakefulness in military personnel : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Nutrition and Dietetics, Massey University, Albany, New Zealand

Abstract

Background: Sleep deprivation (SD) compromises cognitive performance of military personnel, jeopardising operational performance and safety. Since SD-related performance deficits coincide with decreased glucose metabolism in associated brain regions, the ketogenic diet (KD) may mitigate cognitive impairments by providing an alternative fuel source (i.e. ketone bodies [KB]). Aim: To investigate the effect of a 2-week KD compared with a carbohydrate (CHO)-based diet on cognitive function, mood and sleepiness during 36 hours of extended wakefulness. Methods: A randomised, cross-over trial was conducted with 7 military personnel (range, 26- 45 years). Participants ingested a KD (~25 g·day⁻¹ CHO) or CHO-based diet (~285 g·day⁻¹ CHO) for 14 days, immediately followed by 36 hours of wakefulness and separated by a 12-day washout period. Cognitive performance (5-minute Psychomotor Vigilance Task; PVT), mood (fatigue and vigour), subjective sleepiness, and capillary blood glucose and D-β-hydroxybutyrate (D-βHB) concentrations were measured every 2 hours (1, 3 and 5 hours after each meal). Linear mixed models tested the effect of diet, period (6 x 6-hourly bins), test time (1-3) within periods, and their interactions. Results: D-βHB was higher (+0.75 to +1.45 mM; p < 0.001) and glucose was lower (-0.26 to -1.16 mM; p < 0.01) in the KD compared with the CHO-based diet. The KD improved performance for all PVT variables (number of lapses, mean reciprocal reaction time [RRT], slowest 10% RT and fastest 10% RT) (p < 0.05), mood (p = 0.001), and sleepiness (p < 0.001) compared with the CHO-based diet; however, there were no interactions with period or test. Number of lapses and subjective sleepiness increased, and mood, mean RRT and slowest 10% RT deteriorated during the 36 hours of extended wakefulness independent of diet (all p < 0.01). Circadian effects were also observed for fastest 10% RT, mood and sleepiness independent of diet (all p < 0.01). Conclusion: The KD appeared to improve cognitive performance, mood and sleepiness during 36 hours of extended wakefulness compared with the CHO-based diet. This suggests the KD could be considered for military operations when sleep deprivation is anticipated.