Allison E. Avery1, Peggy M. Cawthorn2, Mahalakshmi Shankaran3, William J. Evans3, Kristen M. Beavers1. 1Wake Forest University, Winston-Salem, NC. 2California Pacific Medical Center, Research Institute, San Francisco, CA. 3University of California, Berkeley, CA.

BACKGROUND: Increasingly, the novel D3-Creatine (D3Cr) dilution method is used to directly measure total body muscle mass via stable isotope tracer technology; however, this method has yet to be applied in the context of a geriatric weight loss intervention. The purpose of this preliminary analysis is to derive D3Cr muscle mass estimates of change and variability within the INVEST in Bone Health trial (NCT04076618) to inform future work in this area. METHODS: The parent study is a 3-armed, 12-month randomized, controlled trial designed to determine the effect of weighted vest use or resistance training during weight loss on musculoskeletal health outcomes in 192 older adults. A convenience sample of 24 trial participants are included in this analysis. At baseline and six-months, participants were weighed and ingested a 30 mg D3Cr tracer dose and provided a fasted urine sample 3-6 days post-dose. D3-Creatinine enrichment ratios were measured in stored urine samples using mass spectrometry and total body muscle mass estimates were derived using a published algorithm. Data are presented using descriptive statistics, paired t-tests, and pearson correlations. RESULTS: Participants were older (68.0±4.4 years), mostly white (75.0%), women (66.7%) who were living with obesity (BMI: 33.8±2.7 kg/m2). Over six months of follow up, participants experienced a decrease in body weight (95.0±11.2 vs 84.9±10.6 kg; p<0.01) with no change in D3Cr muscle mass (25.7±8.3 vs 26.2±7.2 kg; p=0.70), and significant increases in percent muscle mass by body weight (27.0±6.7 vs 30.7±6.2 %; p<0.01). Although a significant positive correlation was observed between body weight and D3Cr muscle mass (r=0.49, p<0.01), change in body weight was not significantly correlated with change in D3Cr muscle mass (r=0.27; p=0.21). CONCLUSIONS: Data presented here begin to describe D3Cr muscle mass estimates in the context of an intentional geriatric weight loss intervention and suggest muscle mass can be preserved, despite significant body weight reduction. Future work in this area will examine trial treatment effects and correlate change in D3Cr muscle mass with DXA/CT bioimaging methods as well as physical function. This work was supported by the National Institute on Aging [Grant No. R01AG059186 (KMB)]. Jason Pharmaceuticals, a wholly owned subsidiary of Medifast, Inc. made an in-kind product donation for the meal replacements used in this study.

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