Balancing Kidney Stone Risk with Weight Loss: Dietary Challenges Explored

[Dr. Manoj Monga]
Who are some of your most challenging patients in terms of balancing their stone risk with their other medical conditions? Is it the diabetic who's trying to lose weight? Is it the patient with inflammatory bowel disease? What are some of the more challenging scenarios that you find that makes it harder for patients to follow a diet that prevents stones?

[Dr. Kristina Penniston]
That's a good question. We see so many complex patients in our practice. I can name a few scenarios. One is, after gastric bypass, a lot of patients develop hyperoxaluria, and they have other stone-promoting factors as well. Many of them, because of the reduced gastric volume, are not drinking very much because they need to prioritize the consumption of protein, and they have so little gastric volume that they really can't eat or drink very much.

We often see these patients not only with low urine volume, but then high urine oxalate, and that's because the gastric bypass procedure is malabsorptive, which means that people, essentially, are excreting a lot of calcium in their stool and its transit time in the gut is very short, it's very low, so there's not enough time for calcium to bind with oxalate that patients may be eating, and thereby contributing to more oxalate in the urine.

There may be other sources of oxalate in these patients as well. Sometimes we can get them down to really low oxalate diets and have them using lots of calcium, and they'll still have high urine oxalate. There are studies in rats, a colleague at University of Florida has done some of this work, and others have as well, which shows that there might be other changes from gastric bypass that potentially induce the liberation of oxalate from fat stores, if that's where they were, because some of these patients continue to have high urine oxalate despite our best efforts. That's a problem.

Other patients are others with malabsorptive diseases like Crohn's. Some really serious Crohn's patients or ulcerative colitis have that same problem of malabsorption that I just talked about. Oftentimes, their urine oxalate can be very difficult to control even when they're hardly eating any oxalate at all, so that's frustrating. Of course, if they're vomiting, or if they have a lot of stool, loose stools, fluid in their stools, they can't possibly be drinking enough to compensate for that.

I would say another category of patients who are frustrated, I would say, are people who are on medications like topiramate. Topiramate is a carbonic anhydrase inhibitor. It's very effectively used to combat migraines. These patients often have really, really low urine citrate. Sometimes it's very difficult to raise that urine citrate, that's the effect of that medication. The frustrating part for us is that this medication seems to work so well for migraines that we've had patients say, "Look, these two things are both bad, but I like the fact that my migraines are being controlled." We still don't want them to form stones, so sometimes it's very frustrating that they've given up one health problem only to form another. We work really hard with them on trying to alkalinize their urine, get more citrate, and then increase their fluids. Those are just some examples. I'm sure you have some in your practice too that are pretty hard to treat. What would you say are the most difficult patients?

[Dr. Manoj Monga]
I think many of the things that diabetics are recommended: eating more nuts and trying to find alternative sources for protein. There often tends to be a bit of conflict in terms of what we're recommending and what they have been told to do. Eating more fruits, I think, often is something that's not recommended for diabetics, so there tends to be a bit of a balancing act when it comes to those patients.

[Dr. Kristina Penniston]
I agree. I tell patients with diabetes that there is no reason why we can't converge or integrate stone prevention and diabetes diets, but it is hard, for the reasons you mentioned. I think it can be done, and I think, for example, fruits, a lot of people with diabetes think they can't have fruits, but many dieticians can probably attest to this, that patients can eat fruits if they have diabetes, but usually not by themselves. When you eat fruit with a meal, it tends not to have that same effect quickly on blood glucose that it does when you eat the fruit by itself. There are ways, and maybe that's where a good diabetes dietitian can help you with those patients in integrating those recommendations.

I think another group are people that are losing weight with a ketogenic diet. We also are a big center at UW-Madison for ketogenic diets for seizures. We have an entire nutritional therapy team dedicated to this. Those patients have very acidic urines usually because they're eating a lot of protein and their diets are very high for acid load. Oftentimes, we're using over-the-counter or other types of alkaline strategies because they can't stop the ketogenic diet, especially if it's for seizures. That's a challenging problem to work through sometimes.