In the Time-Restricted Eating: Microbiome and Bone (TREMBO) study, the primary goal is to determine the effect of time-restricted eating with caloric restriction compared to caloric restriction alone on bone health, as well as body weight and the gut microbiota in older women who are overweight or obese.

Time-restricted eating (TRE) has gained increased attention due to the possibility to induce weight loss and improve cardiometabolic health as a result of the purported alignment of circadian rhythm. However, since TRE is often reported to cause a spontaneous reduction of calories, it is not well understood if these health benefits are due to weight loss, circadian rhythm alignment, or a combination of the two. Furthermore, while weight loss can improve cardiometabolic health, it can also induce bone loss, which is problematic in older women who are at a higher risk of fracture. Interestingly, both bone turnover and the gut microbiota are responsive to diurnal variations, such as meal timing, and alterations in the gut microbiota have been associated with differences in bone health. In rodent models, caloric restriction can alter the gut microbiota composition with further alterations shown due to time-restricted eating. This suggests that time-restricted eating could affect bone health, which may be partially mediated by changes in the gut microbiota. Also, lifestyle patterns affects both the microbiota and bone. This randomized controlled trial will use behavior modification to examine TRE plus caloric restriction (CR) to achieve an evening energy deficit compared to CR alone on bone health, as well as body weight and the gut microbiota in older women who have overweight or obese.

Inclusion Criteria:

• Postmenopausal women (>2 years since last menses)
• Body mass index (25-45 kg/m2)
• Agree to be randomly assigned to consume food for ≤ 9 hours/day or ≥12 hours/day
• Must attend on-site visits (about 10) in New Brunswick, NJ, USA (transportation/reimbursement for travel not included)

Exclusion Criteria:

• Participants with >5% weight loss in the past 6 months or extreme dietary/physical activity habits
• An inability to follow the experimental intervention or to perform the required specimen collections
• Antibiotic use in the past 2 months
• Current diagnosis, or history of cancer in past 3 years
• History of surgical procedure for weight loss in the past 3 years
• Current diagnosis or history of bone diseases, type I or II diabetes, gastrointestinal disease, hyperparathyroidism, untreated thyroid disease, significant immune, hepatic, cardiac, or renal disease
• Uncontrolled hypertension or hyperlipidemia in abnormal ranges
• Regular use of medications that affect bone metabolism, including bisphosphonates or hormone replacement.
• A colonoscopy within the past 2 months
• Alcohol or illicit drug abuse
• Current smoker or having quit smoking in the past 3 months
• Shift work
• Participation in another clinical research trial which may interfere with the results of this study.

Women