Ketogenic low carbohydrate, high fat diet in marathon runners

Methodology Single-blind randomized controlled trial. Competitive marathon runners will be randomized to their usual high carbohydrate diet (comparator) or a ketogenic-low carbohydrate, high fat (K-LCHF) diet (intervention) for 6 months. It will not be possible to blind participants to diet group allocation, but outcome assessors will be blinded to the primary outcome during the performance test. Baseline marathon performance will be assessed in the 2023 Sydney marathon. Post intervention performance will be assessed 12 months later in the 2024 Sydney marathon. To reach participant recruitment target, we will recruit a second wave of participants who will perform their baseline marathon in the Sydney 2024 marathon. Post intervention performance for this second group of participants will be assessed 12 months later in the 2025 Sydney marathon. This design allows for real-world running performance to be tested with practicable control for season of the year and racecourse effects on running time. After baseline marathon performance is measured, diet and training will be monitored for 6 months leading into the diet randomization (lead-in diet and training monitoring). Baseline marathon performance and baseline and pre randomization aerobic capacity (VO2max), sex, body composition, as well as training characteristics (overall load, low / high intensity training split) assessed during the lead-in, will be used to pair-match participants. Once matched, participants will be randomly assigned (blinded, random number generator method) to follow either their usual high carbohydrate diet (comparator) or a K-LCHF diet (intervention) for the 6 months leading into the post intervention Sydney marathon. Diet intervention Before being randomized to a dietary intervention group, diet will be assessed at baseline and at 1-month intervals (diet reporting for 2 weekdays and 1 weekend day on each occasion) over a 6-month period (lead-in diet monitoring) using the diet tracking app, EasyDietDiary (Australian based diet tracking App, password protected login access). This will be done to confirm that participants are following a high carbohydrate diet (i.e., following the Australian dietary guidelines) at baseline and during lead-in to the diet intervention. After randomization, participants in the K-LCHF diet intervention group will receive nutritional counselling and resources to assist in learning how to adhere to a K-LCHF diet. The diet intervention will be delivered online and will involve reviewing a series of modules that have been designed specifically for this study. Modules will cover practical knowledge and skills required to follow the K-LCHF diet, including acceptable food items, shopping and meal preparation suggestions presented as written text, figures, and short videos. A module covering training and competition fuelling strategies that adhere to the principles of a K-LCHF diet will also be provided. Reviewing the online learning modules will take approximately 4 hours over the first 2 weeks of the diet intervention. Learning materials will remain accessible at any time during the 6 month intervention. A ketogenic, low carbohydrate diet is a whole food, nutrient rich diet that avoids grains, starches, refined sugars, and most processed foods. Well-formulated ketogenic diets promote the consumption of meat, chicken, seafood, eggs, dairy, leafy and cruciferous vegetables, avocados, nuts, seeds, and berries. Nutritional counselling and monitoring will be overseen by Associate Professor Caryn Zinn, a Registered Dietitian with more than 15 years’ experience. Participants will be asked to use EasyDietDiary to record all food intake for 7 days every week for the first 4 weeks after randomization, followed by 3 days (2 weekdays and 1 weekend day) every month for the remainder of the study (i.e., weeks;1, 2, 3, 4, months; 2, 3, 4, 5, 6). The K-LCHF diet will be prescriptive with regards to macronutrient intake (70% fat, 20% protein, and the lesser of 20 g or 10% nett carbohydrates) but ad libitum for total calories plus or minus 20% of lead-in caloric intake. Participant EasyDietDiary diet information will be reviewed at the end of each diet monitoring assessment block and participants will be advised if any modifications to macronutrient composition, micronutrient requirements or total caloric intake is required. Suggested meal plans and meal recipes will be formulated by the study dietitian to meet subjects’ micronutrient requirements with special attention to sodium intake because higher sodium losses have been shown to occur during very low carbohydrate intake. Diets that are very low in carbohydrates stimulate the production of ketones (an alternate source of fuel when glucose is low) and ketones are considered a valuable biomarker demonstrating adherence to K-LCHF diets. Participants will self-monitor blood ketones throughout the study (blood finger prick sample) by measuring their blood ketone levels. Participants will be provided with a ketone monitor, ketone strips, alcohol wipes and lancets and asked to take replicate (i.e., two measures for increased reliability) blood ketone measurements once per month during the diet intervention. Competition fuelling strategy Participants will be asked to report their marathon race fuelling strategy i.e., the intervals, type, and quantify of fuel consumed during their marathon race. Participants randomized to the K-LCHF diet intervention group will be encouraged to follow the prescriptive diet macronutrient intake (70% fat, 20% protein, and the lesser of 20 g or 10% carbohydrates) on the day of the post intervention marathon race but it may be unreasonable for researchers to enforce this. While it is not unusual for some athletes (even those habitually consuming a standard high carbohydrate diet) to completely avoid carbohydrate consumption during marathon races, unless athletes have previously experimented using a low carbohydrate fuelling strategy, some individuals in this study may not be confident in limiting carbohydrate fuelling during their marathon. To be practical, it is reasonable to accept that an additional carbohydrate allowance during the marathon race, should athletes feel they require it, is in the best interests of the athletes and compatible with the research design. Habitual K-LCHF diet, not marathon race fuelling strategy is the independent variable in this study. Training and athlete monitoring We will use questionnaires within a secure password protected App, StackTeamApp (no cost to participants) to monitor athletes training and general health, including any adverse effects during the diet intervention. The App will assist in managing participant scheduling for attending lab testing sessions and sending in App and text reminders to complete research tasks. This approach is designed to minimize the burden on participants for reporting data. Training loads will be tracked throughout the study and reported as training hours, self-reported intensity splits, training pace, and estimated running distances per week. When available, participants can share training metrics measured using GPS tracking watches and measures of heart rate with researchers. The intervention will not include control over athlete training practices (load and structure). Participants will be asked to select and specify a marathon training plan of their choice at the start of the study and follow the same training plan as closely as circumstances allow, before both the baseline and post intervention Sydney marathons. Participants in this study will be experienced marathon runners and can therefore select any training plan that is compatible with their personalized training approach. Imposing training requirements on experienced marathon runners could affect study outcomes in unexpected ways. For example, it may have unintended negative consequences for recovery, or injury risk, or participant adherence. By having participants report their training plan and carefully monitoring their training practices during the 6-month lead-in phase, and using this information to pair-match participants before randomization, we believe large deviations in training practices at the intervention group level are unlikely. Any differences will be comprehensively measured during the intervention and could be used to better understand variance in individual performances at the end of the trial. Adopting a ketogenic, low carbohydrate diet can be associated with side effects that are usually transient and mild. Common adverse effects, often referred to as “keto flu,” include light-headedness, generalized fatigue, difficulty exercising, poor sleep, and constipation. These typically resolve within days to weeks. Participants can report symptoms or raise concerns any time they feel the need using the StackTeamApp.