To complement the NephMadness Nutrition in Nephrology obesity match-ups, we thought a post on pre-transplant weight loss was timely. According to a recent report published in JAMA, more than one third of the US population are obese (BMI>30) with an estimated medical annual cost of $147million in 2008. Obesity causes heart disease, stroke, type 2 diabetes mellitus and certain types of cancer. According to a recent policy statement of ASCO, obesity is predicted to overtake tobacco as the leading modifiable cause of cancer in the United States in the near future.In the Nephrology world, we are all aware of the survival advantage of obesity in dialysis patients with the so-called “reverse epidemiology” or “obesity paradox” (While obesity, hypertension and hyperlipidemia are indicators of high cardiovascular risk in the general population, in dialysis patients these conditions are associated with a survival advantage). This was demonstrated in several well-conducted studies (ref, ref, ref) in the United States and Europe.
But is there any survival advantage for obese patients while they are waiting for a kidney transplant? Obesity is not an absolute contraindication for transplant listing although some transplant centers do not evaluate patients with BMI >30-35 kg/m2. At our center, we recommend patients should aim for a BMI < 35kg/m2; however we have performed kidney transplants in patients with higher BMIs. Approximately 60% of kidney transplant recipients are overweight, which represents a 116% increase from 1987. But is BMI an accurate reflection of obesity in adults? The answer is no. The accuracy is limited and although a BMI cutoff of >30 kg/m2 has good specificity, it misses more than half of people with excess fat. Newer techniques to evaluate obesity include abdominal circumference, waist to hip ratio, hydrostatic weighing and body fat measuring.
There are concerns about allograft survival, weight gain after kidney transplantation and wound healing. Two retrospective analyses in obese patients undergoing kidney transplantation reported higher rates of delayed graft function, acute rejection, peri-operative complications and worse renal function with higher BMIs.
On the other hand, there is evidence that higher BMIs do not influence outcomes. A study of >164,000 patients demonstrated that low pre-transplant BMI, low pre-transplant serum creatinine (which could be due to sarcopenia), were associated with worse post-transplant outcomes. Bariatric surgery is becoming more popular prior to kidney transplantation and according to this study of USRDS data that evaluated the safety of the procedure, bariatric surgery provides substantial weight loss to kidney recipients. However, it also reported more peri-operative complications and increased mortality in comparison to patients undergoing the same procedure without kidney disease. Significant pre-transplant weight loss (>10kgs) may be a risk factor for peri-operative complications, particularly wound problems. Another study reported that weight loss during transplant listing had no effect on long term outcomes after transplantation and rapid weight loss was associated with subsequent post-transplant rapid weight gain. According to this analysis, the rate of mortality before and after transplantation is unchanged despite weight loss.
In conclusion, there is no evidence that weight loss before transplantation improves long-term outcomes following transplantation although much of the evidence is retrospective and observational in nature. The absence of significant central obesity certainly helps with wound healing and it is intuitive that a ‘healthy weight’ augers well for long term morbidity. How we measure this ‘healthy weight’ however is debatable including where BMI fits into this assessment, if at all.
Hector M. Madariaga,
SUNY Upstate Medical University
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