Comparison Of Weight Loss Associated Change In Muscle Metrics As Assessed By D3Cr And DXA

PURPOSE: Clinical weight loss recommendation remains controversial for older adults, partly due to fat free mass loss and potential exacerbation of age-related functional decline. Historically, weight loss trials have used dual energy x-ray absorptiometry (DXA) to approximate muscle mass. In contrast, the novel D3-Creatine (D3Cr) dilution method directly measures whole body muscle mass; however, it has yet to be applied to a geriatric weight loss intervention. The purpose of this study is to compare changes in DXA lean mass and D3Cr muscle mass measures in older adults experiencing significant, intentional weight loss. METHODS: A convenience sample of 24 older (68.0 ± 4.4 years) predominantly white (75.0%) women (66.7%) living with obesity (BMI: 33.8 ± 2.7 kg/m2) and participating in the ongoing INVEST in Bone Health Trial (NCT04076618) are included in analyses. All participants received a caloric restriction intervention targeting 10% weight loss over a 6-month period, with some randomized to additional resistance training (~33%) or weighted vest use (~33%). At baseline and 6-months, participants were weighed, ingested a 30 mg D3Cr tracer, provided a fasted urine sample 3-6 days post-dosage, and underwent a whole body DXA. Urine was batch analyzed using liquid chromatography-mass spectroscopy to determine D3Crn enrichment, as well as creatine and creatinine levels, and an algorithm was used to estimate total body creatine pool size and whole-body muscle mass. RESULTS: Total body weight was reduced by -10.3 ± 5.7 kg (~11%) over 6 months (p < 0.01). DXA-derived total body lean mass declined from baseline (-0.7 ± 1.3 kg; p < 0.02); however, no change was observed in D3Cr whole body muscle mass (+0.5 ± 5.9 kg; p = 0.70). CONCLUSIONS: Among 24 older adults, significant 6-month weight loss was associated with significant declines in DXA-derived lean mass, while D3Cr muscle mass was unchanged from baseline. Treatment assignment for the trial remains blinded; therefore, full interpretation remains limited. Future work in this area will assess change in D3Cr muscle mass by parent trial treatment group assignment in all study participants.