Keto-lifting: the effect of a ketogenic diet on strength performance

Participants were aged between 20 – 60 years, had at least 6-months experience in Powerlifting / Weightlifting / Crossfit and were free of limiting musculoskeletal injuries at the time of recruitment. Body composition, strength and power, blood analysis and resting metabolic rate were measured at baseline testing. This crossover study design randomly allocated participants to commence the study with either their usual control diet (>250g daily intake of carbohydrates) or a Ketogenic diet (<10% daily intake of carbohydrates) for 3-months. All measures were re-tested after 3-months, and a 2-week ‘washout’ period was imposed where participants were instructed to halve their exercise intensity and volume and continue (or return) to their usual diet. Participants then crossed over to the alternate intervention diet for a period of 3-months, followed by the final data collection. All participants were advised to consume ad libitum and to use kitchen scales to measure food portions. Testing Procedures Baseline, mid and final testing sessions were conducted at Australian Catholic University, Strathfield campus. Measurements were obtained following a 12-hour fast, requiring participants to refrain from consuming any food or beverages, including stimulants such as coffee, for at least 12 hours prior. Participants were instructed not to perform any exercise on the morning of testing. Testing sessions were conducted by accredited exercise scientists. Body composition: Body fat and lean tissue mass were measured by dual-energy X-ray absorptiometry (Medilink Medix DR, 2D-Fan beam, Montpellier, France) from a whole body scan. Measurements were performed at the predetermined scan mode (speed 180 mm/s, resolution 2mm x 2mm, 256 Channel Digital Detector: 72mm x 8mm Collimation) with the analysis software provided by the manufacturer (Medilink – Eazix Software). Participants were required to wear light clothing without zippers or buttons and removed all jewellery for the scanning procedures. The same technologist conducted and analyse all DXA scans. Strength and power assessment: Participants were assessed in the squat, bench press and deadlift exercises or equivalent exercises relevant to their sport (eg: snatch, clean and jerk). Participants were provided with a light warm-up period (2 – 3 minutes walking on a treadmill or stationary bicycle at a self-selected speed). The 1RM protocol commenced with one set of 10 repetitions at approximately 50% of a participant’s known previous maximum strength. Participants then increased resistance over 3 – 6 attempts to reach 1RM with a rest period of 2 mins between sets. The weight lifted for 1RM was recorded when a participant fully executes an exercise correctly with maximal effort. Participants were provided with 20 minutes rest between exercises. Electrolyte balance and blood glucose: Electrolyte balance (Sodium, Potassium and Chloride) and blood glucose were obtained from finger-prick blood samples and measured using a hand-held analyser (iSTAT handheld portable blood analyser, Abbott). Resting metabolic rate: Resting metabolic rate (RMR) was determined using indirect calorimetry (analysis of expired air to determine oxygen consumption and carbon dioxide production). Participants attended the laboratory to undertake RMR testing. The gold standard RMR method was used and involved resting subjects lying supine with a canopy installed over their head. The canopy is designed to regulate air in and out while permitting gas analysis of expired air. Food, ethanol, caffeine, and nicotine affect RMR and their consumption before each test was controlled. Physical activity prior to RMR testing was also controlled. Measurements were approximately 15 minutes in duration with the first 5 minutes deleted and the remaining 10 minutes having a coefficient of variation <10% to be considered valid. Self-reported measures: Throughout each 3-month period, participants were required to record self-reported information about their food/fluid intake, blood glucose/ketone and training data. Participants were instructed on how on to perform these measures at baseline testing sessions. These measures were required 3 times per week but only every 4 weeks. Self-reported measures were collected using online survey software (Qualtrics, Provo, Utah, USA). Access to the online survey were distributed to each participant via email. Macronutrient Composition: Participants were instructed to record their daily food and fluid intake using a smartphone app (MyFitnessPal). Prior to the commencement of the Ketogenic diet intervention, participants received education about what foods were suitable via a list of foods categorised as “green”, “orange” or “red”. During the ketogenic diet, participants were encouraged to eat ad libitum from the green list. The orange list contained foods that can be occasionally consumed and included suggested quantity limits. The red list contained foods that should be avoided in order to maintain nutritional ketosis. Each participant received 30mins of face-to-face education at baseline testing with the primary investigator. Participants were also invited to join an online private social media group to relay instructional videos and menu plans and facilitate on-going communication between participants and the research team. The primary researcher had secure access to user accounts and provided feedback on adherence to the prescribed dietary interventions. Blood ketones and glucose: Participants were instructed on how to self-measure their blood ketones and glucose. Participants were provided with a monitoring kit (Freestyle Optium Neo) which contained a monitor, test strips, alcohol swabs, lancets, a sharps container and latex glove (optional). The test involved one finger prick to obtain a drop of blood for analysis and results were provided within 5 seconds. Training data: Participants recorded information about the number of weekly training sessions, average session length and percent contributions of aerobic exercise, strength training and pre-hab/rehabilitation. Average sessional intensity was also reported, using a 10-point scale.