Energy Deficiency on Hormones in Contraceptive Users

The purpose of the present study is to characterize the endocrine and metabolic responses to a modest, short-term energy deficiency (~250 kcal/day) across the menstrual cycle in recreationally active women using different contraceptive methods. The investigators will be focusing on oral contraceptive users, hormonal IUD, and non-hormonal (i.e., copper IUD). Daily urinary hormone metabolite tracking and comprehensive metabolic assessments (i.e., resting metabolic rate, body composition via DXA, exercise logs, and energy intake) will be used to provide foundational data addressing an important and previously unexamined interaction between energy availability and hormonal regulation in contraceptive users.

Based on evidence that female reproductive hormones are sensitive to energetic stress, that estrogen plays a central role in regulating metabolism and endocrine function, and that hormonal contraceptive methods differentially alter endogenous hormone profiles, the central hypothesis of this study is that a modest, controlled energy deficiency (~250 kcal/day) will alter reproductive hormone profiles across the menstrual cycle in recreationally active women using contraceptives. Specifically, it is hypothesized that changes in urinary reproductive hormone measures will be detectable during an energy-deficient cycle compared to a baseline cycle, and that the magnitude and pattern of these changes will differ by contraceptive type, with hormonal oral contraceptive users demonstrating a different hormonal response to energy deficiency than copper or hormonal intrauterine device users.

A secondary hypothesis is that energy deficiency-induced hormonal changes will be associated with alterations in resting metabolic rate and body composition, and that these associations may be moderated by exercise energy expenditure and perceived stress. Collectively, these hypotheses are grounded in prior research demonstrating hormonal sensitivity to energetic perturbations and the distinct endocrine environments created by different contraceptive methods, while addressing a clear gap in the current literature regarding the interaction between energy availability and hormonal regulation in contraceptive users.

Inclusion criteria

• Female, aged 18-35 years
• Recreationally active (engaging in structured exercise between 8-15 hours per week)
• BMI of 18.5-29.9 as a BMI below or above these cut points results in highly varied menstrual cycle lengths17
• Not currently experiencing an eating disorder or disordered eating, or having a diagnosed eating disorder in the last 3 years
• Non-pregnant or planning to become pregnant
• Medically free from chronic diseases
• Currently using one of the following contraceptive methods for ≥3 months:

Monophasic oral contraceptive

• Hormonal intrauterine device (H-IUD)
• Copper intrauterine device
• Weight stable (no weight change >5% body weight within the past 3 months)
• Weight greater than or equal to 110 lbs
• Not suffering from known gynecological disease (i.e., PCOS, endometriosis, etc.) that may influence menstrual cycle regularity
• Willing and able to maintain current exercise habits throughout the study
• Willing to follow study dietary guidance to achieve a ~250 kcal/day energy deficit during Cycle 2

Exclusion criteria

• Amenorrhea or oligomenorrhea
• Perimenopausal or menopausal
• Currently pregnant, planning pregnancy, or breastfeeding
• Use of hormonal contraception other than monophasic oral contraceptives or hormonal IUD (implant, nuvaring, etc.)
• Initiation or change of contraceptive method within the past 3 months
• Diagnosis of polycystic ovary syndrome (PCOS), endometriosis, hypothalamic amenorrhea, or other known reproductive endocrine disorder
• Current or history of eating disorder or clinically diagnosed disordered eating
• Current participation in intentional weight loss or weight gain program
• Use of medications known to affect metabolism or hormone levels (e.g., systemic corticosteroids, thyroid medications, insulin, GLP-1 agonists)
• Known metabolic, cardiovascular, renal, hepatic, or endocrine disease
• Musculoskeletal injury limiting exercise participation within the past 3 months
• Smoking or nicotine use
• Contraindications to DXA scanning (e.g., pregnancy, recent high-radiation diagnostic imaging exceeding institutional limits)
• Inability or unwillingness to comply with study procedures