Clinical Impact of Preoperative Obesity on Living-Donor Kidney Transplant Recipients in Japan: A Multicenter Experience

<b>Background:</b> Obesity is increasingly prevalent among kidney transplant candidates; however, its impact on graft outcomes in Asian populations is not well characterized. We evaluated the association between preoperative obesity and living-donor kidney transplantation outcomes in Japan. <b>Methods:</b> We analyzed 623 living-donor kidney transplants performed from 1998 to 2021 at six centers in northern Japan. Recipients were categorized by body mass index (BMI) at transplant, and multivariable Cox regression was employed for assessing graft outcomes. <b>Results:</b> Obesity (BMI, ≥30 kg/m²; <i>n</i> = 27 [4.3%]) was the strongest graft failure predictor (hazard ratio, 4.62) compared with normal-weight recipients. Moreover, overweight status (BMI, 25-29.9 kg/m²), acute rejection, and older donor age were independent risk factors. Despite similar rejection rates across the BMI groups, recipients with obesity exhibited persistently impaired kidney function from 1-week posttransplant to the 5-year follow-up. Patient survival was comparable across BMI groups; however, underweight status (BMI < 18.5 kg/m²) was associated with higher mortality. <b>Conclusions:</b> Preoperative obesity and overweight status were significant risk factors for graft failure in Japanese living-donor kidney transplant recipients. Meanwhile, the mortality rate was significantly higher in the patients with underweight status at transplant. Pre-transplant weight optimization and shared decision-making with candidates warrant consideration.