None listed
Conditions
Brief summary
Endurance performance lasting >90 min is limited by carbohydrate stores. Therefore for the past few decades’ researchers have proposed ways to increase the use of fat as a fuel source, reducing reliance on carbohydrate sources during endurance events and ‘sparing’ muscle glycogen. Recent studies have focused on high fat, low carbohydrate diets, which have become increasingly popular amongst athletes, with the expectation of a greater response to training and improved performance. High fat, low carbohydrate diets (~ 65% energy intake from fat) for up to 2 weeks have been shown to increase the use of fat as a fuel source during low to moderate intensity cycling however an improvement in cycling performance is yet to be reported. Another nutritional strategy prescribed to increase the use of fat during training is a high protein, low carbohydrate diet, otherwise known as ‘train low’ (i.e. with low carbohydrate stores). Although both strategies increase the use of fat stores, the complex muscular responses and mechanisms behind these adaptations have yet to be reported. The aim of this study is to determine whether low carbohydrate availability in the presence of high fat or high protein is the driver of the increased fat oxidation and reduced glycogenolysis reported following a 5 day high fat diet.
Interventions
Participants will complete 2 x 12 day interventions.
In both trials, participants will follow a high carbohydrate diet for 5 days and all food and drink is provided by the researchers,. During this time participants will follow their own training program. They will then enter the lab on day 5 for a short exercise test (20 min at 70% VO2max) and a blood sample via venepuncture will be collected pre and post exercise. Expired gas and rate of perceived exertion will be collected during the last 5 m
Participants will complete 2 x 12 day interventions. In both trials, participants will follow a high carbohydrate diet for 5 days and all food and drink is provided by the researchers,. During this time participants will follow their own training program. They will then enter the lab on day 5 for a short exercise test (20 min at 70% VO2max) and a blood sample via venepuncture will be collected pre and post exercise. Expired gas and rate of perceived exertion will be collected during the last 5 min of the exercise. Participants will then enter the lab on day 6 and have their body composition measured using a DEXA scan (dual- energy x-ray absorptiometry), a muscle biopsy will be taken from the quadricep muscle by a certified doctor and an indwelling cannula will be inserted into an anticubital vein in the arm. This will allow for serial blood sample during the exercise protocol. Participants will complete 20 min of exercise at 70% VO2max followed by a high intensity interval session (8 x 5 min exercise with 1 min rests between reps). During the exercise expired gas and rate of perceived exertion will be collected at regular intervals. Participants will then start either a high fat or high protein diet for the next 5 days. During this time participants will complete prescribed training, equating to up to 300 km cycling. Following 5 days of this diet, participants enter the lab and complete another DEXA scan and have another muscle biopsy in the quadriceps and a blood sample via venepuncture (pre and post) before completing 20 min of exercise at 70% VO2max. Expired gas and rate of perceived exertion is collected during the final 5 min of exercise. Participants then follow a high carbohydrate diet for 24 h. Following the 5 days either high fat or protein and the 1 day carbohydrate diet participants will enter the lab and have another muscle biopsy taken and an indwelling cannula will be inserted into one of the anticubital veins. Participants will also be infused with a bolus of 0.37 MBq of U-14C-labelled glucose to measure blood glucose oxidation. Participants will then complete 100 min of cycling at 70% VO2max following by a time trial lasting approximately 30 mins. During the 100 min ride blood samples, expired gas and rate of perceived exertion will be collected every 20 min. Participants have a last biopsy following the 100 min ride. The 12 day interventions will be separated by at least 10 days. The composition of the diets is: High carb diet: 75% energy, carbohydrate, 15 % energy protein, 10 % energy fat. High fat diet: 20% energy, carbohydrate, 15 % energy protein, 65 % energy fat. High protein diet: 20% energy, carbohydrate, 65 % energy protein, 15 % energy fat. Participants will be closely monitored by all staff during their time in the lab. Outside the lab participants will be able to contact the dietitian regarding diet and are required to complete a daily food checklist. They can also contact the student researcher regarding any questions about the rest of the study.
Sponsors
Professor John Hawley
Study design
Allocation
Randomised controlled trial
Intervention model
Crossover
Primary purpose
Educational / counselling / training
Masking
Blinded (masking used) (Investigator, Outcomes Assessor)
Eligibility
Sex/Gender
Male
Age
18 Years to 45 Years
Healthy volunteers
Yes
Inclusion criteria
Well trained cyclists riding more than 200 km per week. A VO2max of > 60 ml/kg/min (this is tested in the lab via a short incremental exercise test on the bike)
Exclusion criteria
Participants will only be excluded if they are unable to follow the dietary intervention due to an allergy or intolerance.
Outcome results
None listed