Gastric Bypass for Kidney Protection?

Before COVID-19, we had (and still have) the obesity epidemic. Obesity has ravaged the physical and mental health of many Americans. It negatively impacts nearly every organ system, including the kidneys. Weight loss is the best antidote but is not easy to achieve. Exercise is difficult to sustain, and medications that suppress hunger or accelerate metabolism are underused and fraught with tolerability issues and adverse effects. Gastric bypass surgery is a relatively new therapy that has had positive effects for those patients who qualify for the procedure. Bypass surgery is considered an efficient method of fighting obesity and has been shown to reduce cardiovascular risk and improve, if not cure, type 2 diabetes.

A paper from Sweden investigated whether gastric bypass in patients with type 2 diabetes would improve kidney function.

This study is your typical retrospective database review that used large national databases, primarily: the Scandinavian Obesity Surgery Register (SOReg) and the National Diabetes Register (NDR). The former contains clinical and epidemiologic information about patients who received gastric bypass; the latter, data for patients with type 2 diabetes. The researchers cross-referenced the databases and divided the patients with diabetes into those who received gastric bypass and those who did not. Four additional databases were used to identify various patient outcomes. The primary outcome was worsening renal function (defined as a 50% or greater reduction in glomerular filtration rate [GFR]), a new diagnosis of chronic kidney disease, or newly developed macroalbuminuria.

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An equal number of patients were analyzed in both groups for approximately 4.6 years. All patients had very high mean estimated GFRs upon study entry (97-100 mL/min/1.73 m²) and were clinically obese (mean body mass index, 41-42 kg/m²). After receiving gastric bypass surgery, patients had a slower decline in estimated GFR (hazard ratio [HR], 0.63; 95% CI, 0.45-0.89) and a slower rise in macroalbuminuria than their nonsurgical counterparts (HR, 0.55; 95% CI, 0.47-0.65). The split happened at about 1 year after surgery and continued throughout the duration of the study period (up to 8 years).

Takeaway

As is typical for a retrospective study, this is more hypothesis-generating than conclusive. Despite their obesity, patients had relatively high kidney function according to both the CKD-EPI and MDRD equations. Although we know that weight loss with gastric bypass confers many health benefits, not all patients qualify for this delicate and complex procedure. In this study, patients with lower baseline kidney function seemed to benefit from gastric bypass, but these results need to be interpreted with great caution, given the study design. The design is why it isn't highly valuable to repeat this study using US data.

A prospective trial is needed, but in the interim, this investigation raises at least two questions in my mind: (1) Is it the magnitude or rate of weight loss that predominantly confers kidney protection, and 2) is there a level of baseline kidney function below which weight loss strategies do not confer clinically significant renal protection?

What are your thoughts about weight loss, gastric bypass surgery, and their effects on kidney function? Share your experiences in the comments below.

Tejas Desai is a practicing nephrologist in Charlotte, North Carolina. His academic interests include the use of social media for physician, student, and patient education. He is the founder of NOD Analytics, a free social media analytics group that serves the medical education community. He has two wonderful children and enjoys spending time with them and his wife.

Follow Tejas P. Desai, MD, on Twitter: @nephondemand

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