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Balancing Kidney Stone Risk with Weight Loss: Dietary Challenges Explored

Author Olivia Reid covers Balancing Kidney Stone Risk with Weight Loss: Dietary Challenges Explored on BackTable Urology

Olivia Reid • Oct 28, 2023 • 126 hits

Dr. Kristina Penniston, a clinical dietician specializing in kidney stones, and urologist Dr. Manoj Monga delve into the intricate relationship between diet, kidney stone risk, and weight management. They discuss challenging dietary scenarios, including post-gastric bypass hyperoxaluria, malabsorptive diseases like Crohn's, and the effects of medications like topiramate on stone formation. The clinicians debate the uncharted territory of intermittent fasting and its potential impact on stone risk, acknowledging the lack of dedicated studies in this area. Dr. Penniston highlights the individualized nature of diet and weight loss, emphasizing the need for sustainable, personalized approaches. Both underscore the multifaceted challenges clinicians face when counseling patients on stone prevention and dietary changes.This article features excerpts from the BackTable Urology Podcast. We’ve provided the highlight reel in this article, and you can listen to the full podcast below.

The BackTable Urology Brief

• Challenging patient scenarios in kidney stone management include those with post-gastric bypass hyperoxaluria, malabsorptive diseases like Crohn's, and medications like topiramate impacting stone formation.

• The effect of intermittent fasting on kidney stone risk remains understudied, despite its associations with weight loss, longevity, and diabetes control.

• Achieving weight loss while minimizing kidney stone risk necessitates lifestyle changes, caloric reduction, increased physical activity, and addressing individual variations in metabolism and response to diets.

Balancing Kidney Stone Risk with Weight Loss: Dietary Challenges Explored

Table of Contents

(1) Navigating Complex Dietary Scenarios in Kidney Stone Prevention

(2) Dietary Strategies for Weight Loss Without Stone Risk

Navigating Complex Dietary Scenarios in Kidney Stone Prevention

Dr. Penniston discusses challenging patient scenarios in kidney stone prevention, emphasizing the complex interplay between stone risk and underlying medical conditions. Patients who have undergone gastric bypass surgery often present with hyperoxaluria due to reduced gastric volume, leading to low urine volume and high urine oxalate. Additionally, patients with malabsorptive diseases like Crohn's face difficulties in controlling urine oxalate levels despite limited oxalate intake. Some patients on medications like topiramate for migraines experience low urine citrate, requiring meticulous efforts to counteract stone formation.

Dr. Monga highlights the difficulties faced by diabetic patients in balancing stone prevention with their dietary restrictions and the challenge of incorporating fruits into their diets. Dr. Penniston lastly addresses patients on ketogenic diets, who often have acidic urine due to high protein and acid load, necessitating alkaline strategies.

[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.

Listen to the Full Podcast

Dietary Modifications for Kidney Stone Prevention with Dr. Kristina Penniston on the BackTable Urology Podcast)
Ep 104 Dietary Modifications for Kidney Stone Prevention with Dr. Kristina Penniston
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Dietary Strategies for Weight Loss Without Stone Risk

Dr. Penniston and Dr. Monga explore the relationship between intermittent fasting, diet, weight loss, and kidney stone risk. They discuss the lack of specific studies on the effects of intermittent fasting on stone risk but acknowledge the growing body of research on its impact on weight loss, longevity, and diabetes control. Dr. Penniston emphasizes that there is no magical one-size-fits-all diet for weight loss and stone prevention, and the key lies in finding a sustainable approach that works for each individual. She states the importance of reducing caloric intake and increasing physical activity but notes that metabolism varies between individuals. Due to the challenges of counseling patients on weight loss and dietary changes, Dr. Penniston stresses the need for personalized approaches.

[Dr. Manoj Monga]
Have there been any studies looking at the effect of intermittent fasting on stone risk?

[Dr. Kristina Penniston]
That's a good question. Oh, gosh, I don't think so, but I can't say for sure. There's been a lot of studies about intermittent fasting and its effect on weight loss, on longevity, and diabetes control. It seems to have some pretty miraculous type effects, although I caution anyone against magical thinking and that any diet is going to be magical. The best diet for patients, especially if it's for weight loss, is the one that works for them.

For some people, intermittent fasting isn't a good way for their families or a good lifestyle, but for others, it can be used. That's a really good question. Does the restriction of eating to certain windows of the day decrease or increase stone risk? I would say if they're drinking throughout the day, including during their non-eating times, that that's a plus, but I don't know of any studies. I'm sure somebody's working on one right now.

[Dr. Manoj Monga]
You mentioned that the best diet to lose weight is the one that works for you, but if we knew that we wouldn't need to diet.

[Dr. Kristina Penniston]
Good point.

[Dr. Manoj Monga]
If a patient was to ask you, "What's the healthiest diet currently that you'd recommend to lose weight and hopefully not increase my risk for stones?" What would you recommend?

[Dr. Kristina Penniston]
My response is probably the least appealing response. It's nothing magical. It's cutting your calories down to the minimum needed to either maintain or lose weight. It's not always as simple as energy in and energy out. That used to be what we thought. It's what I was taught, but we now know that people metabolize the same foods differently. There are studies that show that people eating the same diets, and these are controlled, in hospital studies, they don't lose the same amount of weight, they don't burn the same amount of calories. It's very intriguing, and it gives a lot of us some sort of explanation for why there are some patients who simply can't lose weight or have a hard time losing it.

I do still believe that there's a lot to be said for minimizing your caloric intake and increasing your physical activity. It takes some lifestyle changes and willpower. It takes changes in buying habits. Not having certain foods in your cupboard, in your refrigerator. Not eating maybe between meals. Maybe intermittent fasting. There is something to that, or at least something to a narrower window of eating. You don't have to practice intermittent fasting to simply eat during a certain window of the day.

I do think it's different for people. There are some people who might maybe lose weight only if they exercise really hard or lift weights or something. Other people might be able to do it with diet alone. It's one of the hardest things to counsel people on. I don't specialize in it. I will send a lot of my patients who need to lose weight or want to to my colleagues who specialize in weight loss. There's a lot of science behind that I don't necessarily keep up on.

Podcast Contributors

Dr. Kristina Penniston discusses Dietary Modifications for Kidney Stone Prevention on the BackTable 104 Podcast

Dr. Kristina Penniston

Dr. Kristina Penniston is a clinical nutritionist specializing in therapy for patients with urologic diseases.

Dr. Manoj Monga discusses Dietary Modifications for Kidney Stone Prevention on the BackTable 104 Podcast

Dr. Manoj Monga

Dr. Manoj Monga is the chair of the urology department at UC San Diego in California.

Cite This Podcast

BackTable, LLC (Producer). (2023, June 28). Ep. 104 – Dietary Modifications for Kidney Stone Prevention [Audio podcast]. Retrieved from

Disclaimer: The Materials available on are for informational and educational purposes only and are not a substitute for the professional judgment of a healthcare professional in diagnosing and treating patients. The opinions expressed by participants of the BackTable Podcast belong solely to the participants, and do not necessarily reflect the views of BackTable.



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