Protein and Performance (PROPER) in Endurance Athletes (PROPER)

Reduced Dietary Protein, Performance and Health

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.

Study Overview

• Status: Recruiting
• Conditions: Diet, Healthy; Protein Deficiency
• Intervention / Treatment: Other: Dietary intervention of reduced protein intake; Other: Dietary intervention of normal protein intake

Detailed Description

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
• Enrollment (Anticipated): 20
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Bente Kiens, Professor; Phone Number: +4535321619; Email: bkiens@nexs.ku.dk
• Study Contact Backup: Name: Andreas Fritzen, ass. Prof; Phone Number: +4542633359; Email: amfritzen@nexs.ku.dk

Study Locations

• Denmark
  • Copenhagen, Denmark, 2100
    • Recruiting
    • University of Copenhagen
    • Contact: Nicki W Almquist, Post Doc; Phone Number: +4593601842; Email: nwa@nexs.ku.dk
    • Contact: Andreas M Fritzen, Post Doc; Phone Number: +4542633359; Email: amfritzen@nexs.ku.dk

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 20 years to 50 years (Adult)
• Accepts Healthy Volunteers: Yes
• Genders Eligible for Study: Male

Description

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

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Reduced protein diet; 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; 6-wk dietary intervention of reduced protein intake
Active Comparator: Normal protein diet; 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; 6-wk dietary intervention of normal protein intake

What is the study measuring?

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)

Collaborators and Investigators

• Sponsor: University of Copenhagen
• Collaborators: Maastricht University Medical Center
• Investigators: Study Director: Nicki W Almquist, Post Doc, University of Copenhagen; Principal Investigator: Bente Kiens, Professor, University of Copenhagen

Study record dates

Study Major Dates

• Study Start (Actual): February 23, 2021
• Primary Completion (Anticipated): December 31, 2024
• Study Completion (Anticipated): December 31, 2025

Study Registration Dates

• First Submitted: September 22, 2021
• First Submitted That Met QC Criteria: June 15, 2022
• First Posted (Actual): June 22, 2022

Study Record Updates

• Last Update Posted (Actual): November 7, 2022
• Last Update Submitted That Met QC Criteria: November 2, 2022
• Last Verified: November 1, 2022

More Information

Terms related to this study

• Keywords: Microbiome; Protein intake; Endurance performance; Diet intervention; Health markers; Endurance athletes; Skeletal muscle protein synthesis
• Additional Relevant MeSH Terms: Nutrition Disorders; Deficiency Diseases; Malnutrition; Protein Deficiency
• Other Study ID Numbers: PROPER

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No