Exercise for Better Bones - Day or Night?

• Postmenopausal women within 1-10 yr after menopause
• BMI 18.5-29.9 kg/m2
• Healthy as determined by a screening physical examination and blood chemistry related to thyroid, liver, kidney, and lipid profile within normal range
• No osteoporosis as determined by dual energy x-ray absorptiometry (DEXA) scan at femoral neck or total spinal region
• No regular exercise for more than 30 minutes a day on more than 2 days a week and no physically active employment, such as maintenance and repair or delivery worker
• No regular use of medications known to interfere with calcium and bone metabolism from 6 weeks prior to the study to the end of study such as medications for heartburn, reflux, H2 blockers, diuretics, etc. such as antacids, Maalox, Pepcid AC, Nexium, Diuril, etc.
• Weight stable (within 5 lbs change) for at least 3 months prior to the start of the study
• Willing to maintain usual lifestyle and activities including the same wake-sleep schedule (go to sleep between 10:00 p.m. and midnight with an average 6-8 hours of sleep time)
• Refrain from the use of alcohol and nicotine (for example, cigarettes, cigars, and e-cigarettes) for the length of the study
• Able and willing to perform moderate intensity exercise without contraindications as determined by the Physical Activity Readiness Questionnaire
• Willing and able to stop any nutritional supplements including vitamin D supplements and calcium-containing medications (for instance, calcium-carbonate antacids)
• Willing not to use tanning booths during the study or not to travel to locations with a tropical climate two weeks prior to the study or during the washout period

Exclusion Criteria:

• Hypertension with resting blood pressure higher than systolic 140 and diastolic 90 mmHg
• Within past 6 weeks, had nutrition supplements or medications known to affect calcium metabolism and appetite such as Antacids, Megace, antacids, heartburn, reflux, H2 blockers, diuretics, etc.
• Allergy to any food ingredients used in the provided diet
• Any disorders affecting nutrient absorption or metabolism, such as cystic fibrosis, lactose intolerance, celiac disease, etc.
• Any sleep disorders such as sleep apnea or regular use of an over-the-counter melatonin supplement
• Diabetes or taking medications known to affect bone such as Actos, Avandia, Invokana, etc.
• Engaged in moderate to vigorous exercise or regular exercise for more than 30 minutes/day on more than 2 days/week within past 6 weeks
• Repeated non-compliance with completing prescribed exercise sessions
• Within past 6 weeks, used tanning booths or traveled to location with a tropic climate
• Use of antibiotics (Amoxicillin, doxycycline, etc.), nonsteroidal anti-inflammatory drugs (aspirin, Celebrex, etc.), or probiotics (Lactobacillus, Bifidobacterium) within the past 6 weeks
• Irritable bowel syndrome, inflammatory bowel disease, or not having a bowel movement three days or longer