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Obesity and renal disease

Obesity impacts kidney transplant patients

Obesity appears to lead to additional complications post kidney transplant surgery in obese patients
Doctors need future studies to examine the upper BMI limit at which kidney transplantation should not be recommended for obese patients
Drs Betsy Tuttle-Newhall (left) and Krista Lentine

Obese kidney transplant patients do not as well as normal weight patients following surgery, according to a research review article published in the American Journal of Nephrology.  While obese transplant recipients appear to have worse outcomes compared to normal weight recipients, the authors note that many obese dialysis patients have better long-term survival after a transplant compared with remaining on dialysis.

Saint Louis University investigators examined data from multiple studies to better understand how obesity impacts kidney transplant patients and found that obese patients experienced more adverse outcomes, including wound infections, delayed graft function, graft failure, cardiac disease and increased costs.

Led by Dr Krista Lentine, associate professor of internal medicine in nephrology and Dr Betsy Tuttle-Newhall, director of abdominal transplant at Saint Louis University, the authors concluded that the health outcomes of patients with higher BMI are impinged.

Dialysis

However, doctors are aware of an "obesity paradox" when it comes to dialysis patients, with kidney patients on dialysis appearing to benefit from extra fat, living longer than normal weight patients. Researchers do not know how extra weight provides a protective benefit, but believe that this relative benefit does not occur in transplant scenarios.

They also stressed that the benefit of losing weight prior to a kidney transplant also is unproven and said that further studies were needed to determine whether intentional weight loss before surgery, including diet, exercise and bariatric surgery, does, in fact, improve outcomes.

The current understanding is clouded because the available data does not distinguish between weight lost deliberately, through healthy diet, exercise or bariatric surgery, and spontaneous weight loss due to illness.

Bariatric surgery, in particular, needs to be studied further. Dialysis patients face bigger risks from surgery and it is unknown if it serves to offset the apparent risks of obesity when performed prior to a kidney transplant.

In addition, they found several areas where more study is needed in order to make clear and consistent recommendations about kidney transplants for heavier patients.

"Lifestyle alterations that seem reasonable to improve health outcomes should be encouraged," said Tuttle-Newhall. "Just as we require patients with alcoholic liver disease to stop drinking prior to transplant, it is reasonable to ask kidney transplant candidates to lose excess body fat and attempt to increase lean muscle mass by becoming more physically active and modifying their diet."

"Current guidelines from the American Society of Transplantation recommend a supervised weight loss regimen including a low-calorie diet, behavioural therapy, and a physical activity plan to achieve a BMI<30 prior to kidney transplantation," said Lentine. "But, these guidelines also note that we don't have enough data to determine if some obese patients aren't appropriate candidates to receive kidney transplants at all.”

Lentine added that the study points the way for future research to fill in gaps in our knowledge about how weight affects kidney transplant patients. "For this reason, current acceptable BMI limits for kidney transplant candidates vary across transplant centres."

The authors say future investigations should seek to determine the upper BMI limit at which point kidney transplantation should not be recommended for obese patients. In addition, the researchers note the limitations of BMI alone as a measure of body fat, and suggest further research using more refined measures.

"This review showed us where there are gaps in the existing research and where current data is too light to be able to draw solid conclusions," said Lentine. "These gaps are what 'outcomes research' is designed to remedy. We've figured out some key questions to ask so that we can help our patients have successful transplants and healthy lives."

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