protein and performance (proper) in endurance athletes

Conditions: Diet, Healthy; Protein Deficiency

Summary: the present study is a parallel group design with randomised allocation to either a 1) reduced protein diet (rp) or a 2) normal protein diet (np). the two groups will be pair-matched based on habitual dietary protein intake, endurance training, endurance performance, and sex. the aim of the study is to investigate the effects of reducing dietary protein (\~1g protein/kg body mass) compared to an eucaloric normal protein diet (\~2g protein/kg body mass) for 6 weeks in well-trained endurance athletes on endurance performance, body composition, skeletal muscle protein synthesis, and health-related outcomes. the hypothesis is that endurance performance will maintain or even be improved in well-trained endurance athletes after a 6-week dietary intervention of an eucaloric, protein reduced diet compared to a normal protein rich diet.

design: the present study will include two phases: a 3-week run-in period, and a 6-week intervention of controlled diets containing either a reduced dietary protein (rp) or normal (habitual) protein (np). the run-in period serves as a period for obtaining general activity data and habitual dietary and training habits in order to match the groups before entering the dietary intervention period. subjects and dietary goals: the study is aiming at including 20 male endurance athletes exercising \~15hrs+/week. the 20 males will be pair-matched based on habitual endurance training, habitual dietary protein intake, and endurance performance, and allocated in a randomised order to: 1) a reduced-protein diet (rp) or 2) a normal-protein diet (np). 3-weeks run-in period: after a minimum of 7 days after written consent has been obtained, the run-in period will begin. habitual endurance training volumes will be registered in an online platform (trainingpeaks) and daily activity level will be monitored using an accelerometer (sens) throughout the run-in and diet intervention period. "heavy water" (d2o) will be ingested in a large bolus (3.5ml/kg lbm) upon beginning of the run-in period and plasma enrichments will be maintained throughout the study period by ingesting small daily boluses. this serves to determine skeletal muscle protein synthesis throughout the study. 6-weeks dietary intervention: the diets will be eucaloric and the estimated energy percentages for macronutrients will be as follows: rp - protein \~7e%, carbohydrate \~63e%, fat \~29e%. np - protein \~16e%, carbohydrate \~53e%, fat \~30e%. weekly urine and faeces samples will be collected during the run-in period and dietary intervention and the controlled diets will be supplied weekly for the participants. testing: extensive endurance performance and metabolic testing will be performed prior to-, and during the intervention on weeks -1, 0 (pre), 3 (mid), and 6 (post). the tests include: body composition by dxa-scanning, resting metabolic rate by online respirometry using a vyntus (jaeger, pcx), venous blood-, and skeletal muscle biopsy sampling from m. vastus lateralis, a standardised breakfasts, endurance cycling on an electro-magnetically braked bike (lode excalibur) or running on a motorised treadmill (woodway), and haemoglobin mass measuring using a modified version of the co-rebreathing method. the body mass will be kept unchanged during the 6-weeks dietary intervention.

Eligibility criteria:
inclusion criteria: * endurance athlete * exercising at least 10hrs per week * habitual dietary protein intake \~2g/kg body mass * bmi\<25 exclusion criteria: * food allergies that exclude the controlled diet * inconsistent endurance training load

Keywords: diet intervention endurance athletes endurance performance skeletal muscle protein synthesis protein intake health markers microbiome