Background: Obesity is associated with poor health outcomes in the general population, but the evidence surrounding the effect of body mass index (BMI) on post-liver transplantation survival is contradictory. The aim of this study was to assess the impact of waitlist BMI and BMI changes on the outcomes after liver transplantation.

Methods: Using the Scientific Registry of Transplant Recipients, we compared survival among different BMI categories and examined the impact waitlist BMI changes on post- transplantation mortality for patients undergoing liver transplantation. Cox proportional hazards multivariate regression was carried out to adjust for confounding factors.

Results: Among 38194 recipients, underweight patients had a poorer survival compared to normal weight (HR= 1.3, 95%CI: 1.13-1.49). Conversely, overweight and mildly obese men experienced better survival rates compared to their lean counterparts (HR=0.9, 95%CI 0.84- 0.96, and HR=0.86, 95%CI 0.79-0.93, respectively). Female patients gaining weight over 18.5 kg/m2 while on the waitlist showed improving outcomes (HR=0.46, (95%CI: 0.28-0.76)) compared to those remaining underweight.

Conclusion: The present study supports the harmful impact of underweight on post-liver transplant survival, and highlights the need for a specific monitoring and management of candidates with BMIs close to 18.5 kg/m2. Obesity does not constitute an absolute contra-indication to liver transplantation. Keywords: obesity paradox, survival, underweight, waiting-list, weight change.

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