To our knowledge, this is the largest study to analyse the relationship between BMI or weight change and outcomes after kidney transplantation outside of the United States. Interestingly, BMI was not seen to rise significantly post-transplantation amongst our cohort, with a geometric mean BMI (kg/m2) of 26.6, 27.0 and 27.2 at six-months (P<0.001), one-year (P=0.005) and three years (P=0.522) after transplantation, compared to 27.3 pre-transplantation. After stratifying the cohort by their change in BMI at six months, we noted a higher average one-year creatinine amongst patients with reducing BMI in multivariate analysis (P<0.001), with an adjusted average of 160.6 μmol/l in the BMI reduction cohort, compared to 135.0 μmol/l in the reference stable BMI group. However, there was no significant difference in patient survival, death-censored graft survival or any post-transplant medical complications.
Our results add to the conflicting previous studies in the area. While there are several small single-centre studies on this topic area, analysis including large cohorts are lacking. The most recent analysis comes from Switzerland in an assessment of 777 kidney transplant recipients from 2008 – 2013 (26). Overall post-transplant weight was seen to initially drop in the first six months after transplantation by an average 1.2 kg. Thereafter, post-transplant weight was seen to gradually increase, with a mean 1.2 kg weight gain at 3 years after transplantation compared to the six-month value. El-Agroudy and colleagues performed a similar analysis in 650 kidney transplantation patients between 1990 and 2001 in Mansoura, Egypt (3). In contrast, their study reported a marked increase in body weight in the first six months after kidney transplantation, with a trend for slow increases in subsequent years. Furthermore, this study stratified patients by their six-month BMI into the following cohorts; < 25 kg/m2, 25 - 30 kg/m2 and > 30 kg/m2. In multivariate analysis, the authors reported a significantly increased risk in graft failure and patient death amongst the obese cohort. In addition, they observed higher incidence of PTDM, hypertension and ischaemic heart disease in this obese cohort. However, there are methodological differences between our analyses such as our focus on temporal change in BMI rather than a specific time point.
Interestingly a recent analysis from Harhay et al. identifies pretransplant weight loss prior to transplant of > 10% from listing to transplantation was associated with prolonged hospital stay, increased risk of graft loss (aHR: 1.11, 95% CI: 1.06 – 1.17, p < 0.001) and mortality (aHR: 1.18, 95% CI: 1.11 – 1.25, p < 0.001) relative to the < 5% weight loss cohort. While this measures weight loss prior to transplantation, and ours is after transplantation, we note similar findings amongst our cohort.
While kidney transplant recipients are appropriately counselled regarding the long-term risk of weight gain, it could be argued the immediate period after stressful kidney transplantation may contribute to weight loss rather than gain. While corticosteroid exposure (which is at its highest in the early post-operative period) should contribute to increased appetite, this could be countered by gastrointestinal side effects from mycophenolate mofetil such as nausea, vomiting and/or diarrhoea attenuating appetite. Post-operative complications or severe illnesses could also impact upon nutritional status, and lead to weight loss as opposed to gain, but there were no suggestions of more significant complications in the group that dropped their BMI from our data analysis (either within the first six months or thereafter). It has been reported that kidney transplant recipients objectively drop their frailty scores in the immediate few months after kidney transplantation, compared to time of transplantation, beyond rebounding (27), and our observed drop in BMI could be a surrogate measure of this physiological change. However, frailty status is not a routinely checked parameter after kidney transplantation and therefore we do not have the ability to check for any association.
The importance of our data rests in the lifestyle modification advice we offer our kidney transplant recipients. KDIGO clinical practice guidelines for the care of kidney transplant recipients has the recommendation that; ‘We recommend that patients are strongly encouraged to follow a healthy lifestyle, with exercise, proper diet, and weight reduction as needed’ (28). While this lifestyle intervention advice is relevant long-term, we must ensure adequate advice is offered to prevent BMI loss in recipients early after kidney transplantation where it is not intended (e.g. normal weight at time of transplantation). Patients with chronic kidney disease or dialysis therapy often benefit from renal dietitian input, but this can be lost after kidney transplantation and our study reinforces the value of such allied health professional support in the overall care that is offered to patients after kidney transplantation. This is important in light of our results showing inferior graft function at 12-months after kidney transplantation. Further work is warranted to understand the mechanism behind this and to understand what drives the loss of BMI for some kidney transplant recipients and how this may relate to inferior graft function
There are several limitations to this analysis that we must consider when interpreting the results. This study was retrospective, single centre in design, and we must acknowledge the limitations this provides. Certainly, there will be covariates and confounders that we cannot adjust for in this analysis that could affect graft function and patient survival. For example, the underlying reason for weight loss after kidney transplantation has not been ascertained and this is of critical importance, as BMI loss out of choice as a lifestyle intervention choice will be different to weight due to critical illness. Furthermore, BMI is not an ideal measure of body mass, and does not differentiate muscle and fat mass. However, it provides us with real-world data that can influence the decision-making process to assess post-transplant body mass changes.