The overall aim of this research is to investigate the acute effects of resistance exercise (REx) on the hormonal and behavioral indices of energy balance regulation in breast cancer survivors. This pilot study is designed to provide preliminary data to support future exercise interventions with more comprehensive energy balance profiling.

After screening, eligible and consented participants will complete baseline evaluations of REE, body composition, and subjective questionnaires to assess energy balance. Eligible and interested individuals will attend an exercise familiarization session in the two weeks before the initial study visit. Individuals will then be randomized to either sedentary control/REx or REx/sedentary control in a 1:1. A washout period of approximately 7-14 days will separate testing sessions.

A randomized cross-over short-term study design was chosen to assessment to profile appetite, energy intake, and physical activity in controlled and free-living settings while also reducing participant burden (as opposed to a long-term intervention). Participants will serve as their own controls, thereby circumventing inter-individual variation in physiology that may confound results. It is anticipated that responses to acute exercise will be amplified in chronic interventions and may therefore be used as a basis for generating hypotheses on the regulation of certain energy balance components. The study will end after the completion of 3 days of dietary intake recall and physical activity measurement for the last participant.

Inclusion Criteria:

• Female sex
• Age: 18 - 45 years, since older age may impact appetite regulation45-47 and women >45 are more likely to have begun the menopausal transition (estrogen relates to appetite and eating behavior)
• Body mass index [BMI]: 25 - 35 kg/m2. Since body composition and body mass relate to appetite regulation and energy intake, a narrow BMI range should decrease heterogeneity within the results. The BMI range was chosen to represent a population at risk for developing obesity and associated comorbidities, while also excluding individuals with severe obesity (which may plausibly significantly impact energy intake regulation).
• Pre-menopausal before cancer diagnosis and treatment
• <1 hour/week of planned physical activity by self-report in the previous 12 months, since exercise may alter appetite and response to food
• Diagnosis of primary stage I - II estrogen receptor/progesterone receptor-positive (ER/PR+) breast cancer, according to institutional standards.
• All chemotherapy, radiation, and surgery completed at least two weeks (14 days), but less than 6 months prior to registration

Exclusion Criteria:

• Cancer diagnosis in the last 5 years before breast cancer; any site, excluding melanoma
• History of cardiovascular disease or symptoms suggestive of cardiovascular disease: chest pain, shortness of breath at rest or with mild exertion, syncope
• Diabetes mellitus, uncontrolled hypertension (defined as: systolic blood pressure >160 mmHg or diastolic blood pressure >100mmHg, as measured during the screening visit with participants seated quietly), untreated/uncontrolled thyroid disease, or any other medical condition affecting weight or energy metabolism. Participants who are deemed ineligible based upon uncontrolled hypertension criteria will be referred to their primary care physicians for treatment. If this condition become controlled they will be allowed to be re-evaluated for inclusion in the current trial.
• Unable to exercise due to cardiac, pulmonary, neurological, orthopedic reasons.
• Currently smoking and/or nicotine use.
• Treatment with medications known to significantly affect appetite, weight, energy metabolism, EI or energy expenditure in the last 3 months (e.g. appetite suppressants, lithium, stimulants, anti-psychotics, tricyclic antidepressants).
• Corticosteroid use within the last two weeks
• History of surgical procedure for weight loss at any time (e.g. gastroplasty, gastric bypass, gastrectomy or partial gastrectomy, adjustable banding, gastric sleeve); history of extensive bowel resection for other reasons
• Currently pregnant, lactating or less than 6 months post-partum.
• Score of ≥ 2 on the CAGE (cut-annoyed-guilty-eye opener) questionnaire adapted to include drug use
• Score of > 20 on the Eating Attitude Test - 26 (EATS-26), indicative of disordered eating. Participants with a score >20 on the EATS-26 will be referred to their primary care physician for further evaluation.
• Significant food intolerances/allergies that cannot be accommodated by the University of Colorado Hospital Clinical Translational Research Center (CTRC) Metabolic Kitchen.
• Currently participating in any formal weight loss or physical activity programs or clinical trials for weight loss.
• Other medical, psychiatric, or behavioral limitations that may interfere with participation (as determined by study physician, Dr. Marc-Andre Cornier).
• Unable or unwilling to undergo study procedures

Female Sex