Female Sex HormonesMCOCNCT07258576
Menstrual Cycle vs. Oral Contraceptives: Effects on Muscle Protein Metabolism After Resistance Exercise
A study testing Protein Beverage, Stable Isotope Tracer [D5]phenylalanine and Stable Isotope Tracer [13C]phenylalanine in people with Female Sex Hormones and Menstrual Cycle, run by University of Toronto at 1 site in Canada.
Trial summary
The muscles of the body are constantly breaking down old proteins and building new ones. These two processes, protein breakdown and protein synthesis, together are known as protein turnover. Protein turnover is essential for maintaining healthy muscle. Read more about this study
- Who is it for?
- Ages 18 to 40 years, women onlyHealthy volunteers can take part
- Conditions the study is for
- Female Sex Hormones, Menstrual Cycle, Oral Contraceptives
- What is being tested?
- Protein Beverage, Stable Isotope Tracer [D5]phenylalanine and Stable Isotope Tracer [13C]phenylalanine
- Type of treatment
- Pill or oral medicine
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 20 participants
- Where
- 1 siteCanada
- Study dates
- 20 Jul 2025to 1 Sep 2026
- Phase
- Interventional
- Are there results?
- Not yet: the study is under way
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 to 40 years
- Women only
- Healthy volunteers accepted
- Adult
Who may be able to join
- Age: 18-40 years
- BMI between 18.5-29.9 kg/m2 (non-obese)
- Recreationally active (resistance train minimum twice a week)
- Using monophasic or triphasic oral contraceptives for >1 year (for oral contraceptive users)
- Have regular menstrual cycles (21-35 days) for the past 3 months and discontinued any hormonal contraceptive use for at least 6 months (non-oral contraceptive users)
- Must meet a progesterone sufficiency test (non-oral contraceptive users)
Who cannot join
- Mid-luteal progesterone levels <16umol
- Chronic disease diagnosis (cardiovascular, thyroid, diabetes)
- Current or recent remission of cancer
- Regular use of non-steroidal anti-inflammatory drugs (NSAIDs; except low-dose aspirin), anticoagulants
- Use of prescription drugs that would impact muscle protein synthesis, e.g. Statins, Lithium, ADHD medication.
- Insertion of intrauterine device (IUD) - exception: copper
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- Use of emergency contraception in the last 3 months (e.g. Plan B)
- Severe food allergies (e.g. soy, nuts)
- Smoking, use of performance enhancing drugs (growth hormones, testosterone)
Trial locations and contacts
1 site in 1 country. Contact the study team or a site near you to ask about taking part.
Ines Kortebi, PhD Candidate contact
Canada1 site, 1 recruiting
- Recruiting
Goldring Center for High Performance Sport
Toronto, Ontario, M5S 2C9
Ines Kortebi, PhD Candidate, 6479392755, ines.kortebi@mail.utoronto.ca
About this study
Official title: The Effect of Menstrual Cycle Phase and Oral Contraceptive Use on Muscle Protein Metabolism Post-Resistance Training
The muscles of the body are constantly breaking down old proteins and building new ones. These two processes, protein breakdown and protein synthesis, together are known as protein turnover. Protein turnover is essential for maintaining healthy muscle.
Despite its importance, females have historically been underrepresented in protein metabolism research. A long-standing assumption has been that fluctuations in female sex hormones such as estrogen and progesterone, whether across the natural menstrual cycle or in individuals using oral contraceptives (OCs), make metabolism and training responses too variable to study. Because of this, many researchers have excluded female participants for logistical reasons.
Read more
Resistance exercise, such as weightlifting, is the most effective way to increase muscle size and strength. Each resistance-training session triggers muscle protein synthesis (MPS), the process by which new muscle proteins are built. Consuming dietary protein or individual amino acids further increases the rate at which new proteins are formed. Over time, higher rates of protein synthesis support muscle growth and the maintenance of other lean tissues in the body.
The purpose of this study is to examine how menstrual cycle phases and OC use influence the synthesis of proteins in both muscle tissue and the rest of the body. Improving scientific understanding in this area will support more effective, evidence-based training and nutrition recommendations for females.
- Being tested
- Protein Beverage, Stable Isotope Tracer [D5]phenylalanine, Stable Isotope Tracer [13C]phenylalanine
- Keywords
- Protein Metabolism, Female Sex Hormones, Menstrual Cycle, Oral Contraceptives, Resistance Exercise, Weightlifting, Indicator Amino Acid Oxidation, Stable Isotope Tracer
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Protein BeverageDietary supplement
Participants will consume 16 half-hourly (8 hours) isoenergetic, isonitrogenous beverages containing 1.2 g/kg/d protein.
Stable Isotope Tracer [D5]phenylalanineDietary supplement
Protein beverages will be enriched with the stable isotope [D5]phenylalanine. The use of [D5]phenylalanine will allow for determination of muscle protein synthesis.
Stable Isotope Tracer [13C]phenylalanineDietary supplement
Protein beverages will be enriched with the stable isotope tracer [13C]phenylalanine. The use of [13C]phenylalanine will allow for the determination of the fate of amino acids in the body (incorporation into body protein or oxidation) which can be used to determine protein requirements.
| Study group | Role | What they receive |
|---|---|---|
| Mid-Luteal Phase | Other | 5-9 days post-ovulation Receives: Dietary Supplement: Protein Beverage; Dietary Supplement: Stable Isotope Tracer [D5]phenylalanine; Dietary Supplement: Stable Isotope Tracer [13C]phenylalanine |
| Early Follicular Phase | Other | Days 2-6 post-menses onset Receives: Dietary Supplement: Protein Beverage; Dietary Supplement: Stable Isotope Tracer [D5]phenylalanine; Dietary Supplement: Stable Isotope Tracer [13C]phenylalanine |
| Active Pill Phase | Other | Days 10-20 of active pill Receives: Dietary Supplement: Protein Beverage; Dietary Supplement: Stable Isotope Tracer [D5]phenylalanine; Dietary Supplement: Stable Isotope Tracer [13C]phenylalanine |
| Placebo Pill Phase | Other | At least 48h after last active pill is taken Receives: Dietary Supplement: Protein Beverage; Dietary Supplement: Stable Isotope Tracer [D5]phenylalanine; Dietary Supplement: Stable Isotope Tracer [13C]phenylalanine |
What is being measured
The primary outcome is the main question the study is designed to answer.
Muscle Protein Synthesis (MPS)
Muscle protein synthesis (MPS) will be assessed during an 8-hour post-exercise and feeding period using a stable isotope tracer, L-[ring-D5]phenylalanine ([D5]Phe). The incorporation of the [D5]Phe tracer into myofibrillar muscle proteins, collected from muscle biopsies (pre-exercise and post-8h feeding), will be analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) to determine the fractional synthesis rate (FSR) of muscle proteins. This will help us understand how menstrual cycle phases and oral contraceptive use influence MPS, providing insight into optimizing protein intake and training adaptations in female athletes.
Measured: 8 hours
Secondary outcomes (1)
Whole Body Protein Synthesis (WBPS)
Whole body protein synthesis (WBPS) will be measured over a 4-hour period using the Indicator Amino Acid Oxidation (IAAO) methodology. Participants will consume a stable isotope tracer, L-[1-13C]phenylalanine ([13C]Phe), and breath samples will be collected every 30 minutes during the final 4 hours of the metabolic trial. The enrichment of 13CO₂ in breath samples will be analyzed to determine phenylalanine oxidation rates, providing an estimate of whole-body protein turnover and dietary protein utilization. This will allow us to assess whether hormonal fluctuations influence protein metabolism and nutritional requirements in female athletes.
Measured: 4 hours
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted2 Dec 2025
- Study start20 Jul 2025
- Primary completion1 Sep 2026 (estimated)
- Study completion1 Sep 2026 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for Female Sex HormonesStudies of the same condition, open and under way.
- More trials run by University of TorontoThe sponsor's other registered studies.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase N/A
- Primary purpose
- Basic science
- Allocation
- Randomised
- Intervention model
- Crossover
- Model description
- Between-Subject Crossover Design
- Masking
- None (open label)
- Enrolment
- 20 participants (estimated)
Sponsor and investigators
- Lead sponsor
- University of Toronto
- Sponsor type
- University, hospital or other
- Responsible party
- Principal investigator, Daniel Moore, University of Toronto
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07258576
- Sponsor's protocol ID
- MCOC - REB00048059
- Acronym
- MCOC
- Status last verified
- Nov 2025
- First submitted
- 20 Aug 2025
- Last updated
- 2 Dec 2025
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- Undecided
Study at a glance
From the registry record, last updated by the sponsor on 2 Dec 2025. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- The Effect of Menstrual Cycle Phase and Oral Contraceptive Use on Muscle Protein Metabolism Post-Resistance Training
- ClinicalTrials.gov ID
- NCT07258576
- Acronym / sponsor ID
- MCOC / MCOC - REB00048059
- Keywords
- Protein Metabolism, Female Sex Hormones, Menstrual Cycle, Oral Contraceptives, Resistance Exercise, Weightlifting, Indicator Amino Acid Oxidation, Stable Isotope Tracer
- Study type
- Interventional
- Recruitment status
- Recruiting
- Enrolment
- 20 participants (estimated)
- Lead sponsor
- University of TorontoUniversity, hospital or other
- Study start
- 20 Jul 2025 (actual)
- Primary completion
- 1 Sep 2026 (estimated)
- Study completion
- 1 Sep 2026 (estimated)
- First posted
- 2 Dec 2025 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
The muscles of the body are constantly breaking down old proteins and building new ones. These two processes, protein breakdown and protein synthesis, together are known as protein turnover. Protein turnover is essential for maintaining healthy muscle.
Despite its importance, females have historically been underrepresented in protein metabolism research. A long-standing assumption has been that fluctuations in female sex hormones such as estrogen and progesterone, whether across the natural menstrual cycle or in individuals using oral contraceptives (OCs), make metabolism and training responses too variable to study. Because of this, many researchers have excluded female participants for logistical reasons.
Resistance exercise, such as weightlifting, is the most effective way to increase muscle size and strength. Each resistance-training session triggers muscle protein synthesis (MPS), the process by which new muscle proteins are built. Consuming dietary protein or individual amino acids further increases the rate at which new proteins are formed. Over time, higher rates of protein synthesis support muscle growth and the maintenance of other lean tissues in the body.
The purpose of this study is to examine how menstrual cycle phases and OC use influence the synthesis of proteins in both muscle tissue and the rest of the body. Improving scientific understanding in this area will support more effective, evidence-based training and nutrition recommendations for females.
Study design
- Primary purpose
- Basic science
- Allocation
- Randomised
- Intervention model
- Crossover
- Masking
- None (open label)
- Number of arms
- 4
- Model description
- Between-Subject Crossover Design
| Arm | Type | Receives |
|---|---|---|
| Mid-Luteal Phase | Other | Dietary Supplement: Protein Beverage, Dietary Supplement: Stable Isotope Tracer [D5]phenylalanine, Dietary Supplement: Stable Isotope Tracer [13C]phenylalanine5-9 days post-ovulation |
| Early Follicular Phase | Other | Dietary Supplement: Protein Beverage, Dietary Supplement: Stable Isotope Tracer [D5]phenylalanine, Dietary Supplement: Stable Isotope Tracer [13C]phenylalanineDays 2-6 post-menses onset |
| Active Pill Phase | Other | Dietary Supplement: Protein Beverage, Dietary Supplement: Stable Isotope Tracer [D5]phenylalanine, Dietary Supplement: Stable Isotope Tracer [13C]phenylalanineDays 10-20 of active pill |
| Placebo Pill Phase | Other | Dietary Supplement: Protein Beverage, Dietary Supplement: Stable Isotope Tracer [D5]phenylalanine, Dietary Supplement: Stable Isotope Tracer [13C]phenylalanineAt least 48h after last active pill is taken |
Who may qualify
- Ages
- 18 to 40 years
- Sex
- Female only
- Healthy volunteers
- Accepted
- Age groups
- Adult
Key inclusion criteria (6 listed)
- Age: 18-40 years
- BMI between 18.5-29.9 kg/m2 (non-obese)
- Recreationally active (resistance train minimum twice a week)
- Using monophasic or triphasic oral contraceptives for >1 year (for oral contraceptive users)
- Have regular menstrual cycles (21-35 days) for the past 3 months and discontinued any hormonal contraceptive use for at least 6 months (non-oral contraceptive users)
Key exclusion criteria (9 listed)
- Mid-luteal progesterone levels <16umol
- Chronic disease diagnosis (cardiovascular, thyroid, diabetes)
- Current or recent remission of cancer
- Regular use of non-steroidal anti-inflammatory drugs (NSAIDs; except low-dose aspirin), anticoagulants
- Use of prescription drugs that would impact muscle protein synthesis, e.g. Statins, Lithium, ADHD medication.
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Protein BeverageParticipants will consume 16 half-hourly (8 hours) isoenergetic, isonitrogenous beverages containing 1.2 g/kg/d protein. | Dietary supplement | Active Pill Phase, Early Follicular Phase, Mid-Luteal Phase, Placebo Pill Phase |
| Stable Isotope Tracer [D5]phenylalanineProtein beverages will be enriched with the stable isotope [D5]phenylalanine. The use of [D5]phenylalanine will allow for determination of muscle protein synthesis. | Dietary supplement | Active Pill Phase, Early Follicular Phase, Mid-Luteal Phase, Placebo Pill Phase |
| Stable Isotope Tracer [13C]phenylalanineProtein beverages will be enriched with the stable isotope tracer [13C]phenylalanine. The use of [13C]phenylalanine will allow for the determination of the fate of amino acids in the body (incorporation into body protein or oxidation) which can be used to determine protein requirements. | Dietary supplement | Active Pill Phase, Early Follicular Phase, Mid-Luteal Phase, Placebo Pill Phase |
Primary outcome
Muscle Protein Synthesis (MPS)
Time frame: 8 hours
Muscle protein synthesis (MPS) will be assessed during an 8-hour post-exercise and feeding period using a stable isotope tracer, L-[ring-D5]phenylalanine ([D5]Phe). The incorporation of the [D5]Phe tracer into myofibrillar muscle proteins, collected from muscle biopsies (pre-exercise and post-8h feeding), will be analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) to determine the fractional synthesis rate (FSR) of muscle proteins. This will help us understand how menstrual cycle phases and oral contraceptive use influence MPS, providing insight into optimizing protein intake and training adaptations in female athletes.
1 secondary outcome
Whole Body Protein Synthesis (WBPS)
Time frame: 4 hours
Results and safety
This study is still under way. Results are not available in the source record yet.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 2 Dec 2025.
- Individual participant dataSharing planned: Undecided
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part.
Ines Kortebi, PhD Candidate contact
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A study testing Protein Beverage, Stable Isotope Tracer [D5]phenylalanine and Stable Isotope Tracer [13C]phenylalanine in people with Female Sex Hormones and Menstrual Cycle, run by University of Toronto at 1 site in Canada.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 6 inclusion and 9 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: looking for participants now, as of the sponsor's last update on 2 Dec 2025. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Canada. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
This study is still under way. Results are not available in the source record yet.
How can a doctor refer a patient or contact the research team?
Contact Daniel R Moore, PhD (4169464088, dr.moore@utoronto.ca), or a site near the patient. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Muscle Protein Synthesis (MPS) (time frame: 8 hours). It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 2 Dec 2025.