The effect of a short-term ketogenic diet on cognitive function, sleep, fatigue, heart rate variability and mood.

STUDY DESIGN This study is a randomised, controlled, counterbalanced, cross-over trial. Participants will undertake a 7-day baseline testing period, followed by two intervention periods with a washout period of 12 days. Each intervention period will comprise a 14-day dietary adaptation period and then a 36-h period of extended wakefulness. The study will be conducted at the Aviation Medicine Unit, Royal New Zealand Air Force Base in Whenuapai, Auckland, New Zealand. All participants will be informed of the study’s risks and will be required to provide written consent prior to their participation. FAMILIARISATION, BASELINE TESTING AND DIETARY ADAPTATION Prior to commencing the study, participants will perform the cognitive test battery and questionnaires on 5 separate occasions to familiarise themselves with the protocols and to remove learning effects. Participants will continue ingesting their habitual diet during the 7 days of the baseline testing and then will be required to complete, in a randomised order, a carbohydrate diet or a very-low-carbohydrate, high-fat, ketogenic diet for 14 days during the dietary adaptation period. Participants will be requested to: 1) abstain from over-the-counter medications (e.g. anti-histamines), dietary supplements, alcohol and napping; 2) avoid caffeine, or reduce daily caffeine intake to a maximum of 100 mg ingested prior to 1200 h (i.e. no caffeine can be ingested after 1200); and 3) maintain their normal sleep/wake cycle and physical activity levels. Because the intervention will be applied under free-living conditions, all other lifestyle choices will be allowed to vary naturally; however, participants will be requested to maintain normal lifestyle choices. Participants will be requested to avoid exercising in the 2 hours prior to bed. Daily sleep, daytime subjective sleepiness, mood, hunger, waking heart rate variability and capillary blood glucose and D-b-hydroxybutyrate measurements will be ascertained. Sleepiness, mood and hunger will be measured at 1600 to minimise the influence of time of day on perception. On the morning of day 7 of baseline testing and days 7 and 14 of dietary adaptation, cognitive performance (psychomotor vigilance task, running memory continuous performance test, 2-choice reaction time) will be measured prior to breakfast and exercising. Daily and weekly testing for daytime subjective sleepiness, mood, hunger and cognitive performance will occur within ±0.5 h of the first measure. EXTENDED WAKEFULNESS On the night of day 14 during dietary adaptation, participants will be reminded to continue their habitual sleeping patterns and aim for an 8 h sleep in preparation for the period of extended wakefulness. Sleep duration will be confirmed by actigraphy and a sleep diary. On the morning of day 15, participants will be woken by phone call at 0630 and will not be allowed to fall back to sleep or consume caffeine after waking. Participants will present to the Aviation Medicine Unit at approximately 0700 h to commence a 36-h period of continuous wakefulness from approximately 0730. This period will comprise of 6 x 6-h blocks commencing with a meal. Cognitive performance (psychomotor vigilance task, running memory continuous performance test, 2-choice reaction time), subjective sleepiness, mood, hunger, capillary blood glucose and D-b-hydroxybutyrate will be measured 1, 3 and 5 h following each meal (i.e. 2-h between tests). Participants will remain awake in the laboratory and be continuously monitored; a New Zealand Defence Force Medic will be on call during this time. The environment will be strictly controlled in terms of scheduled activities and environmental conditions. Participants will have free time to read, watch movies, play board games, and interact with other participants and research staff; however, no vigorous physical activity, interaction with people external to the study or use of phones will be allowed. Light exposure will be kept at a constant lux. Ambient temperature will be kept at 20-22 °C. Participants will not be informed of the time. Following completion, participants will be provided with transport home and requested to refrain from duty for a 24-h period to allow for sufficient recovery. DIETARY INTERVENTION For each dietary condition, participants will be provided with comprehensive education from a registered dietitian, including an individualised meal plan specific to the individual’s estimated energy requirements. The ketogenic diet will aim to comprise <40 g/day of carbohydrate, 15-20% energy intake from protein and >75% energy intake from fat. To mitigate reductions in serum electrolytes during the ketogenic diet, participants will ingest an electrolyte capsule (Pure Electrolyte Replacement Capsule; Pure Sports Nutrition, New Zealand) containing 440 mg sodium chloride, 150 mg potassium citrate, 100 mg magnesium citrate and 50 mg calcium citrate, twice daily (i.e. morning and afternoon) and be prescribed high-sodium fluids. Participants will be required to purchase and prepare their own food and fluid. The carbohydrate diet will aim to comprise >45% energy intake from carbohydrate, 15-20% energy intake from protein and <40% energy intake from fat. A registered dietitian will be available at all times, either via phone, email or in person, to provide guidance and support. Water consumption will be encouraged throughout the study. During the 36-h period of extended wakefulness, participants will be provided meals by the research team in accordance with their dietary allocation. Meals will be provided at approximately 0730 h (breakfast), 1330 h (lunch), 1930 h (dinner) and 0130 h (night), with each comprising 25% of the participant’s daily energy requirements (based on habitual energy intake minus 10% for sedentariness). Participants will be instructed not to talk about food and the researchers will avoid discussions about food throughout the period of extended wakefulness. Participants will continue ingesting their prescribed dietary allocation (i.e. carbohydrate or ketogenic diet). Participants on the ketogenic diet will ingest an electrolyte capsule three times daily (i.e. approximately 0800, 1600 and 0000). All meals will be formulated by a registered dietitian. For each group, no caffeine or alcohol will be allowed and only non-caffeinated beverages will be made available, which can be consumed as required. DIETARY MONITORING To monitor dietary compliance, participants will be trained in dietary reporting and requested to provide an image-assisted (alongside a fiducial marker), weighed dietary record in real-time to a registered dietitian via a mobile phone application (WhatsApp; Facebook, San Francisco, CA). Diet records will be required on: 1) 3 non-consecutive days during baseline testing; 2) days 1, 3, 6, 8, 10 and 12 during the dietary adaptation period; 3) and 3 non-consecutive days during the washout period (to confirm participants have returned to their habitual diet). Where under- or mis-reporting is suspected, participants will be required to provide a 24-h dietary recall or repeat the dietary report the subsequent day. If incompliance is suspected, participants will receive dietetic intervention. Each dietary record will be coded (FoodWorks Professional Edition, Version 8; Xyris Software, Australia), with images validating the reported intakes. To help maintain energy balance, participants will report their daily morning body mass and will be advised to prevent a >2% fluctuation. Verification of compliance to the ketogenic diet will be via morning capillary blood D-b-hydroxybutyrate concentrations. During the 36-h period of continuous wakefulness, participants will only be able to consume food provided by the research team and will be under the continuous monitoring of research staff. Participants will measure capillary blood D-b-hydroxybutyrate concentrations every two hours to verify dietary compliance.