What’s the Main Idea?

Learn more about kidney transplants and how obesity can affect their chances of success. This post is based on a recent free access review titled “Obesity in Renal Transplantation” in the journal Nephron.

What Else Can You Learn?

This post also discusses body mass index (BMI): How is it calculated, what are the issues with it, and why is it still used in research and medicine?

What Qualifies Someone for a Kidney Transplant?

Kidney transplants happen when someone’s kidneys have failed or are about to fail. That means that the kidneys are not able to filter waste and excess fluid from the blood. The commonest reason is end-stage kidney disease, also called end-stage renal disease, which is the final stage of chronic kidney disease.

The only alternative to a kidney transplant is dialysis. However, it’s important to note that kidney transplants tend to be the better option. They can restore quality and even longevity of life in a way that dialysis cannot.

Perhaps this is because kidney transplants have become a routine operation. The first attempt was in the 1930s. Success was achieved in the 1950s. The surgical and aftercare procedures are well supported by extensive research and are considered safe, particularly if the patient is healthy and aftercare instructions can be followed. Interestingly, if the kidney comes from a living donor, the transplant tends to last longer.

What Disqualifies Someone from a Kidney Transplant?

There are a number of medical conditions that can disqualify a patient from a kidney transplant. They can be short-term, such as active infections, or long-term, such as certain serious cardiovascular diseases. Lifestyle can also be an issue: Smoking, excessive alcohol consumption and narcotic substance abuse can prevent someone from being a candidate.

The factor we’re interested in today is obesity; specifically, could obesity prevent someone from getting a kidney transplant?

There isn’t a straightforward answer. Obesity can complicate surgery and recovery. It’s a cardiovascular risk factor (CVRF) that is associated with other CVRFs and with metabolic disorders. Over 75% of kidney transplant recipients present at least one CVRF and around 17% die from cardiovascular disease. Obesity can also complicate the graft survival (the survival of the new kidney).

Most kidney transplant centers covered in the free access review “Obesity in Renal Transplantation” recommend that patients on kidney transplant waiting lists lose wait if their body mass index (BMI) is over 35. International guidelines recommend getting the BMI to under 30. However, there isn’t a definitive cutoff point where surgery is not an option. Some centers consider a BMI over 40 to be the point where surgery doesn’t make sense, others say 35, others 30 – each for reasons I’ll go into shortly. First, let’s take a look at why BMI is used and ask whether that’s a fair measurement to use.

What’s the Problem with BMI?

BMI is calculated by dividing a subject’s weight in kilograms by the square of their height in meters. Thus, my BMI would be 22 — that’s 78 kg divided by (1.88 m)2, equaling 22.06 kg/m2. According to the World Health Organization and the United States National Institute of Health, overweight means a BMI over 25 and obese means a BMI over 30.

However, there are some things to consider. The United States National Institute of Health describes how BMI may overestimate body fat in people with a muscular build, such as athletes, and underestimate it in older people, among others. The European Medicines Agency and the World Health Organization have made similar points, as have many individuals with reference to their own experiences with the metric.

The waist circumference or waist-to-hip ratio and the percentage of body fat in combination with BMI could give a better picture of the state of someone’s body. Unfortunately, there isn’t a standardized method to measure the former and there isn’t a reliable and inexpensive way to measure the latter!

Furthermore, it’s very important to consider lifestyle, diet, and risk factors for diseases before making any bold statements about someone’s health based solely on their weight or size.

Despite the problems, BMI is still used as a measurement in research and medicine because it is correct roughly 80% of the time. In research, this is sufficient to make some general statements and recommendations. In medicine, it can be a starting point for further discussions.

Can a Kidney Transplant Work for Someone with a High BMI?

As mentioned, there isn’t a definitive universal cutoff BMI for kidney transplants. However, there are some things that can be considered, as summarized in “Obesity in Renal Transplantation”.

Patients with a BMI up to 40 show better survival rates after a kidney transplant than with long-term dialysis. However, patients with a BMI over 30 are more likely to have complications during surgery and complications with the graft starting to function. What’s more, in the long term, the transplanted kidney is less likely to survive if the patient’s BMI is over 30.

All that said, it is essential to look at each individual as more than just BMI: Weight distribution, body shape, muscle mass and fluid accumulation (which is common with kidney failure) all need to be considered.

Does Weight Loss Help?

There isn’t enough evidence to say that weight loss is beneficial. Clinical trials on the benefits of pre-transplant weight loss would be needed to make clear recommendations. However, many centers still recommend weight loss because of the potential to reduce surgical complications, prevent delays in graft function, and improve long-term graft survival. In general, self-care, moderate exercise and a healthy diet are important for people with chronic kidney disease.

If your doctor recommends that you lose weight, you might be interested in my post “Increasing the Success of Behavioral Approaches to Weight Loss”. It talks about some of the things you might consider when trying to lose weight, such as emotional support or compensating for changes in your body’s structure and energy demands.

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