Patrick Lowry, MD, discusses the scope of both obesity and stone disease, surgical and other challenges unique to managing stone disease in the obese, and steps obese adult and pediatric patients can take to lower their stone risk.
Q. Can you frame for readers the problem of obesity and stone disease?
A. To start with, it's important to talk about the problem of obesity and how it is ballooning, for lack of a better word, in our country. Before 2001, not a single state in the United States had a prevalence of obesity-defined as a body mass index over 30-greater than 20%. In 2001, Mississippi became the first state with more than 20% of its population having a BMI over 30. Ten years later, nine states have a prevalence of obesity of over 30%. Sadly, in Louisiana and Mississippi, more than one-third of the population is morbidly obese.
Q. Please explain what those metabolic changes are.
There's increasing evidence that patients with metabolic syndrome show more abnormalities that relate to increased risk of urinary stone disease. Metabolic syndrome is the loosely defined syndrome that, by most definitions, includes increased abdominal girth (increased BMI), hypertension, insulin resistance, and dyslipidemia. Dr. Dean Assimos' webcast from the 2011 AUA annual meeting (available at http://www.aua2011.org/program/webcasts.html) describes in more detail the role of the metabolic syndrome. Diabetes, hypertension, coronary artery disease, and increased BMI are associated with an increased risk of kidney stones.
Q. What should obese patients do about their risk of stone disease?
A. First, the patient must lose as much weight as possible. They don't have to become a slim person, but with significant weight loss, their stone risk will decrease.
Second, with or without weight loss, there are steps they can take to decrease their stone risk. Number one is adequate fluid intake so that they're maintaining enough urine output to keep their urine dilute. Number two is citrate supplementation, as that is an inhibitor of calcium stone disease. Number three is decreasing their protein intake-all animal protein, not just red meat-to decrease their acid load. Finally, they should decrease their salt intake, which will decrease their calcium excretion. Those are four pretty simple actions that any patient can take, and they specifically address the factors that increase the risk of stones in obese patients.