Investigators explore relationship between obesity and kidney stone formation

Obesity increases the risk of kidney stone disease, and some weight loss strategies actually increase the risk, according to an article published in Reviews in Urology.¹

Obesity is a growing health problem among adults in the United States. The Centers for Disease Control and Prevention, which defines obesity as a body mass index (BMI) of 30 kg/m2 or higher and severe obesity as a BMI of 40 kg/m2 or higher, reported that from 1999 to 2018, the age-adjusted prevalence of obesity among US adults increased from 30.5% to 42.4%, and the prevalence of severe obesity increased from 4.7% to 9.2%.²

“Obesity is linked with multiple comorbidities and also associated with an increased kidney stone risk,” the authors wrote.

Severely obese adults, for example, are at increased risk of diabetes, hypertension, and hyperlipidemia, comorbidities that can result in systemic and body organ changes contributing to kidney stone formation, according to the study.

“With the rising prevalence of both stone disease and obesity, the authors felt that it was pertinent to review the current data,” said study author Kyle Wood, MD, assistant professor of urology at University of Alabama at Birmingham. “Oftentimes as urologists, we surgically manage our [patients with kidney stones], but forget that we may be able to intervene with both dietary advice and medical management, and this may prevent future stones. Understanding why obesity impacts kidney stone disease allows for a more informed discussion and prevention plan.”

The study results showed that BMI, waist circumference, and weight are positively associated with people’s risk of developing incident kidney stones. And patients who are obese or overweight are more likely to have urinary risk factors for stone formation, including higher calcium, oxalate, and urate excretions.

Patients who are obese tend to develop calcium oxalate stones and uric acid stones, and there’s good evidence that obesity and low urine pH are associated, according to the authors.

Animal and human studies have shown that inflammation and oxidative stress, which are associated with obesity, also appear to play a role in kidney stone inflammation.

Obesity may affect how medications aimed at preventing stones work. Patients who are obese and have kidney stone may be more resistant to standard stone-prevention medication dosing regimens than patients who are not obese. As a result, some patients may need more adjustments to therapy or additional agents in their treatment plans.

Weight management sounds like a solution, but study results suggest the weight loss approach matters. For example, weight loss treatment with the lipase inhibitor orlistat (Xenical) may reduce urinary citrate excretion and increases urine pH, setting the stage for calcium phosphate stone generation. And although malabsorptive bariatric procedures have been shown to increase the risk for kidney stone development, restrictive bariatric operations for weight loss have not.

More research is needed to better define the mechanisms involved in obesity and kidney stone development, the investigators wrote.

“Evaluating our patients [with kidney stones] and their medical comorbidities, including obesity, in a holistic way will only improve their care. Our hope is this paper increases awareness among urologists, leads to a more critical evaluation of stone formers with obesity, and improves medical and dietary recommendations,” Wood said. “This review also demonstrates that there is still a lot that is unknown. Hopefully, these voids in knowledge can be filled with the current scientific research. With improved knowledge, there will hopefully be the development of more therapeutic options.”

References

1. Poore W, Boyd CJ, Singh NP, Wood K, Gower B, Assimos DG. Obesity and its impact on kidney stone formation. Rev Urol. 2020;22(1):17-23.

2. Hales CM, Carroll MD, Fryar CD, Ogden CL. Prevalence of obesity and severe obesity among adults: United States, 2017-2018. NCHS Data Brief. February 2020. Accessed October 22, 2020. https://www.cdc.gov/nchs/data/databriefs/db360-h.pdf