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.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
NONE
Enrollment
20
6-wk dietary intervention of reduced protein intake
6-wk dietary intervention of normal protein intake
University of Copenhagen
Copenhagen, Denmark
Endurance performance on a bike
Endurance performance defined as maximal aerobic power (Wmax) during incremental test to exhaustion on a bike measured as 1-minute mean power output (W)
Time frame: From Pre (week0) to post (week6)
Microbiome
Diversity of bacterial strains in gut microbiome measured in feces samples
Time frame: Run-in (week-3 to week0) vs dietary intervention (week0 to week6)
Resting metabolic rate
Measured in an over-night fasted state via indirect calorimetry expressed in MJ/day
Time frame: Pre (week0) to mid (week3)
Resting metabolic rate
Measured in an over-night fasted state via indirect calorimetry expressed in MJ/day
Time frame: Pre (week0) to Post (week6)
Lean body mass
Measured by dual-energy x-ray (DXA)-scanningg expressed in kg
Time frame: Run-in (week-3) to Pre (week0)
Lean body mass
Measured by dual-energy x-ray (DXA)-scanning expressed in kg
Time frame: Pre (week0) to Post (week6)
Total fat mass
Measured by dual-energy x-ray (DXA)-scanning expressed in kg
Time frame: Pre (week0) to Post (week6)
Total fat mass
Measured by dual-energy x-ray (DXA)-scanning expressed in kg
Time frame: Pre (week0) to mid (week3)
Total fat mass
Measured by dual-energy x-ray (DXA)-scanning expressed in kg
Time frame: Run-in (week-3) to Pre (week0)
Power output at 4mmol/L blood lactate
Alterations in Power output at 4mmol/L blood lactate in response to diet
Time frame: Pre (week0) to mid (week3)
Power output at 4mmol/L blood lactate
Alterations in Power output at 4mmol/L blood lactate in response to diet
Time frame: Pre (week0) to Post (week6)
Fractional utilisation of maximal oxygen uptake at 4mmol/L blood lactate
Alterations in Fractional utilisation of maximal oxygen uptake at 4mmol/L blood lactate in response to diet
Time frame: Pre (week0) to mid (week3)
Fractional utilisation of maximal oxygen uptake at 4mmol/L blood lactate
Alterations in Fractional utilisation of maximal oxygen uptake at 4mmol/L blood lactate in response to diet
Time frame: Pre (week0) to Post (week6)
Maximal oxygen uptake VO2peak
Alterations in Maximal oxygen uptake VO2peak measured by an online VO2 apparatus
Time frame: Pre (week0) to mid (week3)
Maximal oxygen uptake VO2peak
Alterations in Maximal oxygen uptake VO2peak measured by an online VO2 apparatus
Time frame: Pre (week0) to Post (week6)
Peak power output on a 10-seconds sprint
Alterations in peak power output on a 10-seconds sprint in response to diet
Time frame: Pre (week0) to mid (week3)
Peak power output on a 10-seconds sprint
Alterations in peak power output on a 10-seconds sprint in response to diet
Time frame: Pre (week0) to Post (week6)
Mean power output on a 10-seconds sprint
Alterations in mean power output on a 10-seconds sprint in response to diet
Time frame: Pre (week0) to mid (week3)
Mean power output on a 10-seconds sprint
Alterations in mean power output on a 10-seconds sprint in response to diet
Time frame: Pre (week0) to Post (week6)
Gross efficiency on a bike
Gross efficiency expressed as % of external power compared to internal (metabolic) power
Time frame: Pre (week0) to mid (week3)
Gross work efficiency on a bike
Gross efficiency expressed as % of external power compared to internal (metabolic) power
Time frame: Pre (week0) to Post (week6)
15-minute time-trial power output on a bike
Alterations in 15-minute time-trial mean power output
Time frame: Pre (week0) to mid (week3)
15-minute time-trial power output on a bike
Alterations in 15-minute time-trial mean power output
Time frame: Pre (week0) to Post (week6)
Fractional utilisation of maximal oxygen uptake during 15-minute time-trial
Alterations in Fractional utilisation of maximal oxygen uptake during 15-minute time-trial
Time frame: Pre (week0) to mid (week3)
Fractional utilisation of maximal oxygen uptake during 15-minute time-trial
Alterations in Fractional utilisation of maximal oxygen uptake during 15-minute time-trial
Time frame: Pre (week0) to Post (week6)
Respiratory exchange ratio
respiratory exchange ratio (RER) during rest and exercise using indirect calorimetry
Time frame: Pre (week0) to Post (week6)
Respiratory exchange ratio
respiratory exchange ratio (RER) during rest and exercise using indirect calorimetry
Time frame: Pre (week0) to Mid (week3)
Training load
Training load as quantified by Edward's Training Impulse based on heart rate zones
Time frame: Run-in (week-3) vs dietary intervention (week0 to week6)
Energy intake
Habitual energy intake registered by food diaries expressed in Mega Joules
Time frame: Run-in (week-3) vs dietary intervention (week0 to week6)
Energy expenditure
Energy expenditure is measured by combining resting metabolic rate and daily activity recording from accelerometer data and heart rate monitor
Time frame: Run-in (week-3) vs dietary intervention (week0 to week6)
Blood lactate concentration
Glucose lactate measured in fasted state on an ABL800
Time frame: Run-in (week-3 to week0) vs dietary intervention (week0 to week6)
Blood glucose concentration
Glucose concentration measured in fasted state on an ABL800
Time frame: Run-in (week-3 to week0) vs dietary intervention (week0 to week6)
Blood amino acid concentration
Amino acid concentration measured by ELISA
Time frame: Run-in (week-3 to week0) vs dietary intervention (week0 to week6)
Plasma metabolomics
Plasma metabolomics by chromatography-mass spectrometry
Time frame: Run-in (week-3 to week0) vs dietary intervention (week0 to week6)
Skeletal muscle protein expression
Alterations in Skeletal muscle protein expression
Time frame: Pre (week0) to mid (week3)
Skeletal muscle protein expression
Alterations in Skeletal muscle protein expression
Time frame: Pre (week0) to Post (week6)
Haemoglobin mass expressed in grams
Haemoglobin mass measured via inhalation of carbon monoxide (CO) using the modified CO-rebreathing method
Time frame: Pre (week0) to mid (week3)
Haemoglobin mass expressed in grams
Haemoglobin mass measured via inhalation of carbon monoxide (CO) using the modified CO-rebreathing method
Time frame: Pre (week0) to Post (week6)
Blood volume in ml
Blood volume measured via inhalation of carbon monoxide (CO) using the modified CO-rebreathing method
Time frame: Pre (week0) to Post (week6)
Blood volume in ml
Blood volume measured via inhalation of carbon monoxide (CO) using the modified CO-rebreathing method
Time frame: Pre (week0) to Mid (week3)
Energy expenditure measured as energy intake to maintain body weight
Daily energy intake during intervention measured in Mega Joules
Time frame: Run-in (week-3 to week0) vs dietary intervention (week0 to week6)
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