Liver and Kidney volume Reduction May Underlie Metabolic Adaptation After Metabolic Bariatric Surgery: A sub-study of the "POWER" Randomized clinical trial.

BACKGROUND AND AIMS: Metabolic bariatric surgery (MBS) is highly effective for weight loss, yet up to 50 % of individuals regain weight within five years. Reductions in resting metabolic rate (RMR), linked to fat-free mass (FFM) loss, have been suggested as one contributing factor. Yet, the liver and kidneys are highly metabolic organs (∼30 % of RMR); therefore, changes in their volume may contribute to a greater-than-expected decline in RMR, known as metabolic adaptation (MA), which may promote weight regain. We aim to evaluate the impact of exercise on changes in organ volume and MA following MBS.

METHODS

Fifty-eight adults with severe obesity (39.6 ± 10.6y, 114.3 ± 17.5 kg, 41.4 ± 4.1 kg/m2) were enrolled in an open-label randomized controlled trial and assigned to one of three exercise intervention groups pre MBS: aerobic (n = 15), resistance (n = 13), combined training (n = 14), or to a no-exercise control group (n = 16) for 26 weeks. Training sessions were online, supervised, and progressed to 60 min, three times/week. Pre- and post-intervention RMR was measured by metabolic cart, body composition by dual-energy X-ray, and liver and kidney volume using 3-T magnetic resonance imaging (MRI).

RESULTS

Fifty-three participants (91 %) completed the intervention, and 47 were included in the final analysis. Significant reductions were observed in body weight (-31.1 ± 8.7 kg, -27 %), RMR (-356 ± 237 kcal/day, -17 %), kidney volume (-35.1 ± 25.2 cm3, -11 %), and liver volume (-384 ± 250 cm3, -21 %) (p < 0.01 for all), similarly across all groups. Crucially, reductions in liver and kidney volume were significantly associated with lower RMR (p < 0.001). The significant (P < 0.001) MA of -289 ± 190 kcal/day was independent of exercise volume or type. Liver volume accounted for 32.1 % of MA, FFM for 29.7 %, and kidney volume for 6.2 %.

CONCLUSIONS

Our findings suggest that MA following MBS may be associated with a reduction in liver and kidney volume, potentially contributing to RMR decline. These findings highlight a potential organ-specific mechanism underlying MA and may prevent weight regain.

CLINICALTRIALS: gov identifier: NCT04777305.