August 17, 2023
What is BMI, why do transplant centers care about it, and how can you reach a healthy weight? Golnaz Ghomeshi Friedman, a renal dietitian and certified clinical transplant dietitian, Melanie Pina, a peritoneal dialysis patient, and Carol Murray, a living kidney donor, discuss this and more.
What is BMI?
BMI stands for body mass index. It is an estimate of body fat based on height and weight.
There are four BMI categories:
- Underweight: Less than 18.5
- Normal weight: 18.5–24.9
- Overweight: 25–29.9
- Obesity: BMI of 30 or greater
"The calculation is your weight in kilograms divided by your height in meters squared," said Friedman. "BMI is a good screening tool because it's a quick calculation with information that we typically have on people, like their height and weight. However, it doesn't tell us about that specific individual, their characteristics, or body composition (how weight is distributed)."
For example, two five-foot and three-inch tall people who weigh 130 pounds would have the same BMI but could look vastly different from each other. Many centers rely solely on BMI, but others have begun using it in conjunction with other measurements like central adiposity.
"Looking at the central adiposity, or the accumulation of fat in one's midsection, can be really helpful here. How much weight is in the belly compared to the person's height can be a good indicator of future health problems," said Friedman. "We know there are people at a higher weight and BMI that are healthy, meaning they don't have diabetes or pre diabetes, their blood pressure is well controlled, they eat well, and they exercise regularly. That's why we want to look at the entire patient, in addition to weight."
Learn more about risk factors associated with obesity.
Why do transplant centers care about weight?
Weight is used to determine surgical risks for the donor and recipients.
"Each individual transplant center determines the weight limitations for recipients. Some use BMI, others use BMI in addition to central adiposity, while others don’t use BMI at all, “Friedman said. "Some have absolute contraindication, meaning you cannot get a transplant if your BMI is above a certain number. Many centers are moving away from this, though, using BMI and other parameters to determine surgical and long-term risks."
One of the biggest risks, infection after surgery, is directly tied to weight but in a way that may surprise you.
"A transplanted kidney is placed in the lower abdomen. That tends to be where many people carry a lot of weight. More weight in that central region can complicate the surgery because the surgeon has to make a much bigger incision to place the kidney. The more tissue and fat cut through, the higher the risk of bleeding, infection, and other surgical complications," said Friedman. "Transplant recipients have to be on medications that suppress their immune system so that they don't reject the new kidney. Those medications make it hard to fight off infection. So, if the transplant recipient gets an infection from the larger surgical wound, the body can't fight it off."
There is also some evidence of long-term complications for transplant recipients at higher weights.
"Individuals with a higher weight at time of transplant may experience delayed graft function, meaning they may require dialysis after transplant, than those at a lower weight. There may also be a higher risk or death," Friedman said. "Weight in the middle is also correlated with a higher risk of developing diabetes or high blood pressure, the main causes of kidney disease."
The risk of developing diabetes or high blood pressure is also why transplant centers care about the weight of kidney donors.
"We want donors to have the lowest risk of developing diabetes or high blood pressure as possible," said Friedman. "We want them to live the longest, healthiest life they can with a single kidney."
Learn more about weight before and after a kidney transplant.
How can you safely lower your weight?
Potential donors and transplant recipients can safely lose weight in many ways including working with a dietitian to create a healthy diet plan, exercising, and weight loss surgery.
For Carol Murray, a kidney donor to her husband, exercise and diet helped her shed enough weight to become a living donor.
"Overall, I was healthy. My blood pressure was spot on and I had no indication of diabetes, but I knew for years that my BMI was at an unhealthy level. So, me working to lose weight and lower my BMI helped me as much as him,” said Carol. “I needed to lose 65 pounds, so I went on a low carbohydrate diet and exercised more than I used to. I watched my husband continue to decline so it didn't feel like it was happening fast enough but I lost about a pound per week which is quick."
After eight months, Carol reached her goal BMI and donated to her husband. It's been four years since then, and she and her husband are thriving. Some, however, cannot lower BMI through diet and exercise alone. They may find weight loss surgery helpful.
"There are two primary surgeries, gastric sleeve and gastric bypass. A gastric sleeve is a non-malabsorptive surgery, meaning you can still absorb nutrients. A portion of the stomach is removed, so the stomach is smaller. This can change your hormones in terms of your fullness and satiety hormones," Friedman said. "A gastric bypass is a more restrictive surgery because a portion of the stomach and intestine is removed. Food bypasses some of the intestines where nutrients are absorbed. The less you absorb, the less weight you gain."
Melanie Pina, a peritoneal dialysis (PD) patient, gained weight from the PD sugar solution despite eating well and exercising. She opted for weight loss surgery.
@melanie.pina I show my body at the end! 7 month update after the gastric sleeve surgery #weightlosssurgery #gastricsleeve #gastricsleevesurgery #gastricsleevejourney #7months ♬ original sound - Melanie Pina
"After four months of PD, I gained fifteen pounds. My BMI went up and I was knocked off the transplant waitlist. I was frustrated because I didn't have blood pressure issues or diabetes. I was healthy. I spoke to a nephrologist, heartbroken, because I didn't know what to do. They suggested weight loss surgery," said Melanie. "The weight loss surgeon was incredible. As someone who was big their whole life, you feel invisible, but he made me feel seen. He explained that bigger people can be healthy and skinnier people can be unhealthy. He reiterated that my weight wasn’t due to laziness."
Melanie's surgeon explained that many factors affected her health and recommended a gastric sleeve.
"I wanted the gastric bypass but he explained that gastric sleeves are better for people who take pills because of the absorption. I met with a nutritionist and psychologist, who asked if I had an eating disorder and what my relationship with food was like,” Melanie said. “Had I gone through the weight loss surgery a few years ago, it wouldn't have worked because it isn't a quick fix. You still have to put the work in. It is just a tool that aids you."
Melanie returned to normal four days after the surgery: "It was an amazing experience. I cried after the surgery and because I knew my life was going to change. Two months later, my BMI dropped enough to get back on the transplant waitlist.”
Wondering how to become a kidney donor or get onto the kidney transplant weight list? Sign up for the Kidney Learning Center.
Ask questions and get answers
Our Patient Information Help Line, NKF Cares, supports people affected by kidney disease, organ donation, and transplantation. Call toll-free at 855.NKF.CARES (855.653.2273) or email nkfcares@kidney.org.
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