Menstrual Cycle vs. Oral Contraceptives: Effects on Muscle Protein Metabolism After Resistance Exercise (MCOC)

University of Toronto

Status: Enrolling

Conditions: Protein Metabolism; Female Sex Hormones; Oral Contraceptives; Menstrual Cycle

Treatments: Dietary Supplement: Stable Isotope Tracer [13C]phenylalanine; Dietary Supplement: Protein Beverage; Dietary Supplement: Stable Isotope Tracer [D5]phenylalanine

Study type: Interventional

Funder types: Other

Identifiers

NCT07258576

MCOC - REB00048059

Details and patient eligibility

About

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.

Enrollment: 20 estimated patients

Sex: Female

Ages: 18 to 40 years old

Volunteers: Accepts Healthy Volunteers

Inclusion criteria

• 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)

Exclusion criteria

• 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
• 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 design

Primary purpose: Basic Science

Allocation: Randomized

Interventional model: Crossover Assignment

Masking: None (Open label)

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20 participants in 4 patient groups

Mid-Luteal Phase

Other group

Description:

5-9 days post-ovulation

Treatment:

Dietary Supplement: Stable Isotope Tracer [D5]phenylalanine

Dietary Supplement: Protein Beverage

Dietary Supplement: Stable Isotope Tracer [13C]phenylalanine

Early Follicular Phase

Other group

Description:

Days 2-6 post-menses onset

Treatment:

Dietary Supplement: Stable Isotope Tracer [D5]phenylalanine

Dietary Supplement: Protein Beverage

Dietary Supplement: Stable Isotope Tracer [13C]phenylalanine

Active Pill Phase

Other group

Description:

Days 10-20 of active pill

Treatment:

Dietary Supplement: Stable Isotope Tracer [D5]phenylalanine

Dietary Supplement: Protein Beverage

Dietary Supplement: Stable Isotope Tracer [13C]phenylalanine

Placebo Pill Phase

Other group

Description:

At least 48h after last active pill is taken

Treatment:

Dietary Supplement: Stable Isotope Tracer [D5]phenylalanine

Dietary Supplement: Protein Beverage

Dietary Supplement: Stable Isotope Tracer [13C]phenylalanine