Protein and Performance (PROPER) in Endurance Athletes

Study Overview
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Brief Summary
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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.

Detailed Description
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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.

Official Title
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Reduced Dietary Protein, Performance and Health

Conditions
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Diet, Healthy, Protein Deficiency

Intervention / Treatment
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* Other: Dietary intervention of reduced protein intake
* Other: Dietary intervention of normal protein intake


Participation Criteria
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Eligibility Criteria
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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

Ages Eligible for Study
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Minimum Age: 20 Years
Maximum Age: 50 Years

Sexes Eligible for Study
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Male

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Parallel Assignment
Interventional Model Description: A pair-matched group, parallel design within each sex
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Reduced protein diet<br>A 6-week eucaloric dietary intervention of reduced protein intake ( 1g protein/kg body mass). The diet will, hence, contain  7E% protein,  63E% carbohydrate, and  29E% fat. Participants are free-living and receive all food pre-packed from the study kitchen. The energy provision will be set to match energy balance. | Other: Dietary intervention of reduced protein intake<br>* 6-wk dietary intervention of reduced protein intake<br>|
| Active Comparator: Normal protein diet<br>A 6-week eucaloric dietary intervention of normal protein intake ( 2g protein/kg body mass). The diet will, hence, contain  16E% protein,  53E% carbohydrate, and  30E% fat. Participants are free-living and receive all food pre-packed from the study kitchen. The energy provision will be set to match energy balance. | Other: Dietary intervention of normal protein intake<br>* 6-wk dietary intervention of normal protein intake<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| 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) | From Pre (week0) to post (week6) | 
| Microbiome | Diversity of bacterial strains in gut microbiome measured in feces samples | Run-in (week-3 to week0) vs dietary intervention (week0 to week6) | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Resting metabolic rate | Measured in an over-night fasted state via indirect calorimetry expressed in MJ/day | Pre (week0) to mid (week3) | 
| Resting metabolic rate | Measured in an over-night fasted state via indirect calorimetry expressed in MJ/day | Pre (week0) to Post (week6) | 
| Lean body mass | Measured by dual-energy x-ray (DXA)-scanningg expressed in kg | Run-in (week-3) to Pre (week0) | 
| Lean body mass | Measured by dual-energy x-ray (DXA)-scanning expressed in kg | Pre (week0) to Post (week6) | 
| Total fat mass | Measured by dual-energy x-ray (DXA)-scanning expressed in kg | Pre (week0) to Post (week6) | 
| Total fat mass | Measured by dual-energy x-ray (DXA)-scanning expressed in kg | Pre (week0) to mid (week3) | 
| Total fat mass | Measured by dual-energy x-ray (DXA)-scanning expressed in kg | 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 | 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 | 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 | 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 | Pre (week0) to Post (week6) | 
| Maximal oxygen uptake VO2peak | Alterations in Maximal oxygen uptake VO2peak measured by an online VO2 apparatus | Pre (week0) to mid (week3) | 
| Maximal oxygen uptake VO2peak | Alterations in Maximal oxygen uptake VO2peak measured by an online VO2 apparatus | 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 | 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 | 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 | 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 | Pre (week0) to Post (week6) | 
| Gross efficiency on a bike | Gross efficiency expressed as % of external power compared to internal (metabolic) power | Pre (week0) to mid (week3) | 
| Gross work efficiency on a bike | Gross efficiency expressed as % of external power compared to internal (metabolic) power | Pre (week0) to Post (week6) | 
| 15-minute time-trial power output on a bike | Alterations in 15-minute time-trial mean power output | Pre (week0) to mid (week3) | 
| 15-minute time-trial power output on a bike | Alterations in 15-minute time-trial mean power output | 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 | 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 | Pre (week0) to Post (week6) | 
| Respiratory exchange ratio | respiratory exchange ratio (RER) during rest and exercise using indirect calorimetry | Pre (week0) to Post (week6) | 
| Respiratory exchange ratio | respiratory exchange ratio (RER) during rest and exercise using indirect calorimetry | Pre (week0) to Mid (week3) | 
| Training load | Training load as quantified by Edward's Training Impulse based on heart rate zones | Run-in (week-3) vs dietary intervention (week0 to week6) | 
| Energy intake | Habitual energy intake registered by food diaries expressed in Mega Joules | 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 | Run-in (week-3) vs dietary intervention (week0 to week6) | 
| Blood lactate concentration | Glucose lactate measured in fasted state on an ABL800 | Run-in (week-3 to week0) vs dietary intervention (week0 to week6) | 
| Blood glucose concentration | Glucose concentration measured in fasted state on an ABL800 | Run-in (week-3 to week0) vs dietary intervention (week0 to week6) | 
| Blood amino acid concentration | Amino acid concentration measured by ELISA | Run-in (week-3 to week0) vs dietary intervention (week0 to week6) | 
| Plasma metabolomics | Plasma metabolomics by chromatography-mass spectrometry | Run-in (week-3 to week0) vs dietary intervention (week0 to week6) | 
| Skeletal muscle protein expression | Alterations in Skeletal muscle protein expression | Pre (week0) to mid (week3) | 
| Skeletal muscle protein expression | Alterations in Skeletal muscle protein expression | 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 | 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 | Pre (week0) to Post (week6) | 
| Blood volume in ml | Blood volume measured via inhalation of carbon monoxide (CO) using the modified CO-rebreathing method | Pre (week0) to Post (week6) | 
| Blood volume in ml | Blood volume measured via inhalation of carbon monoxide (CO) using the modified CO-rebreathing method | Pre (week0) to Mid (week3) | 
| Energy expenditure measured as energy intake to maintain body weight | Daily energy intake during intervention measured in Mega Joules | Run-in (week-3 to week0) vs dietary intervention (week0 to week6) | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Diet intervention, Endurance athletes, Endurance performance, Skeletal muscle protein synthesis, Protein intake, Health markers, Microbiome