Application of the D(3)‐creatine muscle mass assessment tool to a geriatric weight loss trial: A pilot study

BACKGROUND: Traditionally, weight loss (WL) trials utilize dual energy X‐ray absorptiometry (DXA) to measure lean mass. This method assumes lean mass, as the sum of all non‐bone and non‐fat tissue, is a reasonable proxy for muscle mass. In contrast, the D(3)‐creatine (D(3)Cr) dilution method directly measures whole body skeletal muscle mass, although this method has yet to be applied in the context of a geriatric WL trial. The purpose of this project was to (1) describe estimates of change and variability in D(3)Cr muscle mass in older adults participating in an intentional WL intervention and (2) relate its change to other measures of body composition as well as muscle function and strength. METHODS: The INVEST in Bone Health trial (NCT04076618), used as a scaffold for this ancillary pilot project, is a three‐armed, 12‐month randomized, controlled trial designed to determine the effects of resistance training or weighted vest use during intentional WL on a battery of musculoskeletal health outcomes among 150 older adults living with obesity. A convenience sample of 24 participants (n = 8/arm) are included in this analysis. At baseline and 6 months, participants were weighed, ingested a 30 mg D(3)Cr tracer dose, provided a fasted urine sample 3–6 days post‐dosage, underwent DXA (total body fat and lean masses, appendicular lean mass) and computed tomography (mid‐thigh and trunk muscle/intermuscular fat areas) scans, and performed 400‐m walk, stair climb, knee extensor strength, and grip strength tests. RESULTS: Participants were older (68.0 ± 4.4 years), mostly White (75.0%), predominantly female (66.7%), and living with obesity (body mass index: 33.8 ± 2.7 kg/m(2)). Six month total body WL was −10.3 (95% confidence interval, CI: −12.7, −7.9) kg. All DXA and computed tomography‐derived body composition measures were significantly decreased from baseline, yet D(3)Cr muscle mass did not change [+0.5 (95% CI: −2.0, 3.0) kg]. Of muscle function and strength measures, only grip strength significantly changed [+2.5 (95% CI: 1.0, 4.0) kg] from baseline. CONCLUSIONS: Among 24 older adults, significant WL with or without weighted vest use or resistance training over a 6‐month period was associated with significant declines in all bioimaging metrics, while D(3)Cr muscle mass and muscle function and strength were preserved. Treatment assignment for the trial remains blinded; therefore, full interpretation of these findings is limited. Future work in this area will assess change in D(3)Cr muscle mass by parent trial treatment group assignment in all study participants.