BackTable / Urology / Podcast / Transcript #104

Podcast Transcript: Dietary Modifications for Kidney Stone Prevention

with Dr. Kristina Penniston

In this episode of BackTable Urology, urologist Dr. Manoj Monga (UC San Diego) and clinical nutritionist Dr. Kristina Penniston (UW Madison) discuss the role of diet in kidney stone prevention and how urologists can partner with dietitians to create integrated stone clinics. You can read the full transcript below and listen to this episode here on BackTable.com.

(1) Partnering with Dieticians

(2) The Role of Diet in Kidney Stone Formation

(3) Managing Fluid Intake for Kidney Stone Prevention

(4) Sodium Intake & Kidney Stones

(5) The Role of Protein Sources in Kidney Stones

(6) Dietary Sources of Oxalates

(7) Managing Complex Kidney Stone Cases

(8) Optimal Diet for Kidney Stone Prevention

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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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[Dr. Manoj Monga]
Hello everyone, and welcome back to the BackTable podcast, your source for all things urology. You can find all previous episodes of our podcast on iTunes, Spotify, and at backtable.com. It's a pleasure today to have Dr. Kris Penniston joining us as our guest. Dr. Penniston is a senior scientist at the University of Wisconsin in Madison, where she's been with the Department of Urology for 18 years. She's an international authority on diet and kidney stones. As a registered dietician, she looks after patients in an integrated fashion through a multidisciplinary stone clinic at the University of Wisconsin. In addition to this, she has her PhD and has been very active in driving the science behind kidney stone prevention. Dr. Pennistson, welcome, and thank you for joining us today.

[Dr. Kristina Penniston]
Thank you for having me, Manoj. It's a pleasure to be here.

[Dr. Manoj Monga]
Maybe we could start off with a little bit about yourself. How did you decide to become a dietician, and what brought you to our world in urology?

[Dr. Kristina Penniston]
I had earned a bachelor's degree in African-American history and went out in the world and worked for a couple of years, and then I decided to return to school. I ended up getting a second bachelor's degree in dietetics because I became very interested in health. I didn't think I wanted to become a medical provider, doctor, if you will, so I just decided that nutrition was something I liked and I would pursue it. It turned out that I was really good at biochemistry and some of the other things.

I got that bachelor's degree. Then in Madison, we have this wonderful university hospital. I knew I wanted to stay in the area, and so I decided to apply to an accredited internship for dietetics here at UW Health at University Hospital. I also applied to grad school at the same time because I knew that if I wanted to practice at a university hospital as a dietician, I would need a master's degree, which is required now of all dieticians. I think next year is the first year it will be required, but at university hospitals, it's been a thing for a long time.

I did the internship, went to grad school, and really liked research a lot. After my master's degree, I just continued on and got a PhD. It was then that I decided that I didn't want to necessarily follow in my professor's footsteps and become an academic researcher. I wanted to do both. I wanted to be a clinician scientist. I had been working four hours a week in the metabolic stone prevention clinic at University Hospital, all the while I was earning my PhD.

I got the PhD, and Dr. Stephen Nakada, who's the chair of the department of urology, said, "I suppose you'll be leaving us now to pursue a position as a professor somewhere." He said, "What if I could create a scientist position for you in our department of urology, and then you could continue doing the stone clinic and researching stones?" By that time, I was already hooked. I realized that there was a lot of interesting chemistry in stones, and I was a dietician already and had been seeing patients and developing those relationships, so it was an easy decision for me to say yes.

(1) Partnering with Dieticians

[Dr. Manoj Monga]
You mentioned accredited internships. Are there any internships that specialize in kidney stone prevention?

[Dr. Kristina Penniston]
That's a great question. The answer is no. In fact, there's not a whole lot of education that dieticians and prospective dieticians get with respect to treating kidney stones with nutrition therapy. I think this is because there's so much attention placed on the big diseases: diabetes, of course, there's a whole bunch of nutritional strategies for that, cardiovascular disease, and some of the GI diseases. I think this lack is in part because so much attention is focused on that, but also because I think kidney stones are complicated. I'm not sure that that's an excuse for why it's not taught. All I know is that most dieticians come out of their programs without ever having learned anything about kidney stones and nutrition.

[Dr. Manoj Monga]
If one of our urologists in the audience was hoping to start a clinic with a dietician as their partner, how would one identify that individual, and how would one help educate or fill the gaps in the education that might have been there during their schooling?

[Dr. Kristina Penniston]
First, I really hope that urologists do look for dieticians to partner with. I know from hanging around urologists for so many years that there's not enough time in a day for a urologist who's got a busy clinic and a busy surgical practice to do the kind of therapy that's really needed. Even me, I see a lot of patients in a day, but not as many as a urologist does, so I still have time to do the counseling.

I would say that a urologist should look in his or her hospital and make contact with the director of clinical nutrition. All hospitals are required to have registered dietician/nutritionists as part of their accreditation with JCAHO. Now, not all hospitals have to have outpatient dieticians, which is probably what you would want in a stone clinic, but many do. In fact, many of the academic settings, where probably some of the audience members are, have more than enough dieticians to meet their minimum requirements.

There may be some available FTE. If you go to your clinical nutrition director and say, "Hey, I've got this stone clinic. It's multidisciplinary. Here's all the evidence for the role of nutrition therapy. I would really keep this person busy. Let's work on that." That's one idea. If that doesn't work, and typically it doesn't because there's not as many dieticians as there are a need for, then I would suggest finding a local dietician to whom you could refer your patients. In both cases, whether you get one in hospital or find one in the community, you're undoubtedly going to have to expose that dietician to education, if not educate him or her yourself, look for some sources to do that.

There are sources. There's a lot of publications and a manual that we use in the Academy of Nutrition and Dietetics called the Nutrition Care Manual. There's a chapter there about kidney stones and nutrition. Those are two suggestions that I have for getting a dietician for your practice. The only other way is to actually include a dietician and reimburse that dietician through your practice. This may not be appealing, but as you may or may not know, dieticians are not reimbursed for most of the nutrition therapy services that we provide by Medicare, and so a lot of what we do is considered value-added.

(2) The Role of Diet in Kidney Stone Formation

[Dr. Manoj Monga]
Dr. Penniston, no question, it is value-added, but it sounds like there are a few other logistics to work around. In the interim, maybe let's see what knowledge we can share with our audience today. Perhaps we'll start with not prevention but stone passage. Patients often come in and say, "I saw on the internet I'll drink a liter of Coke or I'll do some cod liver oil." A variety of things that I suspect have been tested with time, but maybe not with science. Are there any things that you've heard of that may actually work to help kidney stones pass?

[Dr. Kristina Penniston]
Not many things. Unfortunately, even the idea of pushing fluids while passing a stone, while many of my patients say that that's what helps them pass stones, there actually isn't the best evidence for that that it’s actually going to hasten kidney stone passage. I think it would be a good instinctual thing to do when you're trying to pass a stone, but drinking Coca-Cola, taking cod liver oil, doing any kind of supplements or anything like that to hasten passage, there's no evidence.

[Dr. Manoj Monga]
The patient fortunately has passed their stone. They're in the clinic now saying, "What did I do wrong? How do I prevent the next one?" What do you say?

[Dr. Kristina Penniston]
My first comment is going to be: you didn't do anything wrong. Many times, diet is not the reason the patient formed the stone. I like to point that out because I think it manages patients' expectations. I think if we insist on blaming the patient or trying to find a dietary cause for every type of stone and every patient's stone, we're going to miss the mark. Not all stones are caused by diet, many are caused by genetics, many are caused by underlying medical conditions that have systemic influences that predispose one to stones, some are caused by medications, and probably most are caused by a combination of all of those things. I like to tell the patient, "You didn't do anything wrong, but there might be something we can optimize or something we can improve in the diet."

What I consider myself is sort of a diet detective, if you will. The patient comes to me, they probably passed their stone as you said or had surgery. One of the first things I want to do is try to figure out if diet even likely contributes to their stone risk. The way I do that is by looking at all the same diagnostic things that a urologist does. I'll look at 24-hour urine results. I'll look at relevant blood values. I'll look at medical history and medications. Then, I also do a very comprehensive diet assessment. Over the years, I've developed a stone-targeted assessment, if you will. Given that there are many types of stones, more than just calcium, for example, and given that there are many different risk factors, there can be a lot of things to explore. I like to consider myself the detective that's either ruling in or out a dietary cause for stones. Often I can find something, like I said earlier, to improve, even if I'm not convinced it was the actual reason they formed the stone.

[Dr. Manoj Monga]
Does the detective work take a formal structure in terms of dietary logs or recall? Then, the other question would be for the individual who perhaps doesn't want to do a 24-hour urine collection, are there empiric recommendations that you would recommend for everyone?

[Dr. Kristina Penniston]
Right, I'll take the second question first. There's a lot of debate about whether a 24-hour urine collection should just be one or whether it should be more than one, and whether it's really effective or useful. I think it is. I think that the real power of it though is in monitoring the effects of therapy over time. I do think it's useful for patients to do a 24-hour urine collection and hopefully, it won't be their one and only because you'll want to test how your therapy is working on their risk parameters. If a patient doesn't want to do it, or if their insurance won't cover it, or if the urologist simply doesn't think it's necessary, I can still do a lot. I can still do a very targeted diet assessment.

I will sometimes ask people to bring in diet logs, but there are some pitfalls to that. Any dietician listening might relate to this. When you tell a patient beforehand that you're going to be looking at certain things in their diet or that you're going to even just be looking at their diet, they will often change how they eat. I could say, "Manoj, here's this diet log, spend three days filling it out, and then we'll talk about it when you see me next." I've already planted in some patients' minds some terror there, like they're going to get in trouble with the dietician if they admit what they ate, so I don't do that very often.

What I like to do is on-the-spot; I like to query the patient in a couple different ways. I'll query them about what they ate over the last two days, if they can recall, and then I'll ask some very targeted questions about how they habitually eat. For example, based on the information I got from the 24 or 48-hour recall, I might say things like, "In a typical week or in a typical month, how many times do you have X?" Then I go through my list, and I'm able to piece things together. What I really want is a picture of their habitual diet. I don't even really want to know so much about how they ate on the day of their urine collection because that too is something patients will alter their behavior for when they do that. I really like to get an on-the-spot, no predispositions, no fear, and also, dieticians can relate to this.

I think urologists, it's good for them to know this. For many patients, diets are very personal, how they eat is really personal, and their dietary habits. You want to try to get it, things that they don't want to admit to you and things that they feel guilty about and you want to get portion size. None of that is possible if the patient feels you're going to judge them. It's really important, and dieticians are especially equipped to do this, to give the patient the space and the feeling that he or she is respected no matter what they say because you always want the truth and not just something that they want you to hear. Those are some strategies that I have found useful.

(3) Managing Fluid Intake for Kidney Stone Prevention

[Dr. Manoj Monga]
Is it one-size-fits-all for fluid intake, or what do you set as the target for each patient?

[Dr. Kristina Penniston]
You asked about empiric suggestions, like if a patient doesn't do a 24-hour urine. My answer to that was, I'll do a diet assessment because I still want to be targeted. I still want to provide some sort of personalized approach rather than saying, "Here's eight things that most people do. I'm not sure any one of them might work for you, but do them all." Even in the absence of 24-hour urine, I believe I can elicit information that will help me target my directions.

Let's say fluids is one. Let's say I know from their diet assessment that they don't drink very much because I'll ask people to tell me what they drink in a day, and we'll work together and figure out the ounces that that is. I'll show them a typical glass or something, and they'll tell me about that. Or if I have the urine collection and it shows volume under two liters, then I will say, "We need to increase your fluid intake."

I don't think there's a one-size-fits-all approach to everyone. People are of different body sizes, that means they have different body surface areas and that means that a larger person is going to lose more fluids through their skin than a smaller person. People have different consistency of their bowel movements; some are more watery than others. We exhale water, so not all of the things we drink go right through our kidneys.

I'll somewhat target the fluid intake to the size of the person, but in general, we know that in order to produce, let's say at least two liters of urine, one has to usually drink at least three liters of fluids. I'll target that as a good goal or if I want the patient to produce more urine, I might go higher. If the patient is a very aggressive athlete, I can presume that they would sweat a lot, they'll need to replace even more.

Then as far as particular fluids, I think a lot of patients feel like we are only talking about water. I have a lot of patients who don't like water or who can't drink the water at their homes because of contamination or they have well water that they don't drink or something. I think it's important for us, not only to help people identify the amount of fluids they should drink, but also which fluids. I think we can be generous and very broad and tell patients basically all fluids count. Of course, we want you to drink as many low-sugar, low-calorie, low-alcohol beverages as possible, but there's even room for those things as well.

I've worked with patients to figure out ways to flavor their waters with fruit or vegetables or to use water alternatives. I work a lot with patients on scheduling their fluid intake. A lot of people don't seem to respond to thirst. Sometimes it requires using your cell phone to beep at you every couple of hours to drink, or I do some techniques like give people rubber bands to wear around their wrist, five rubber bands, and then I'll give them a water bottle, and I'll say, "Every time you finish one of these, take off a rubber band, and by the end of the day they should all be gone or you know, you still have some drinking to do." I think there's a lot of ways we can be creative about fluids and very targeted.

[Dr. Manoj Monga]
Hard water, soft water, alkaline water: Is the type of water important?

[Dr. Kristina Penniston]
In general, I would say no. All waters are fluids, and they will all contribute to urine output. I think if I reframe the question a little bit, patients always want to know, "What's the best water?" Magical thinking like, "What's the best thing I should drink?" I always say, "All of them." There is evidence that hard water, because of the minerals that it contains, oftentimes magnesium is one of those, actually can prevent kidney stones. I'm not sure that it alone can do so. Of course, it would depend on the type of stone the patient was forming. I think there's benefits of hard water.

There's concern about soft water because it might contain sodium chloride. Well, it’s not really as much as people have thought or people think. There's evidence, people have looked at it and measured it, and there's a very small amount of sodium in soft water, in most cases. Then alkaline waters, it depends on how the water is made alkaline. If the water has been made alkaline because of the addition of sodium bicarbonate or some other bicarbonate or bicarbonate precursor, then that could be very beneficial for patients who need to increase their alkaline load of their diet and the alkaline load that the kidneys experience. Other waters that are made of alkaline pH but they don't have those ingredients in them aren’t going to do anything, they're not magical, they're not special in any way.

(4) Sodium Intake & Kidney Stones

[Dr. Manoj Monga]
For sodium, is 1500 milligrams your target?

[Dr. Kristina Penniston]
That's pretty low. The general ballpark milligrams per day that is recommended by the USDA and other authorities is generally 2,300 to 2,400 milligrams of sodium. 1,500 is often touted for congestive heart failure. There are some studies, if you look in the literature, that suggest that there are no added benefits to eating that little sodium. Now, it depends on the study's outcomes and what they were looking at and what they were measuring, but I don't think people have to be quite that restrictive. I think that we can, again, take this somewhat individually.

The main concern with sodium, in the form of sodium chloride in particular, is that it may induce hypercalciuria because of the expansion of extracellular volume that it creates, but not every patient has hypercalciuria. Even patients with high salt intakes, I might not place that as a high priority on their diet recommendations unless they also have hypercalciuria. Yes, I think most people need to restrict their salt, and I work with a lot of patients to do that, but it's not always the number one priority for everyone.

(5) The Role of Protein Sources in Kidney Stones

[Dr. Manoj Monga]
For uric acid, portion size or moderation, I think, is critical for animal protein. Is there a difference between red meat, white meat, fish, eggs, or is it all the same? It all boils down to portion control?

[Dr. Kristina Penniston]
That's a hot topic. It's a hot topic in chronic kidney disease, which is not necessarily related to kidney stones. What I think we're learning from that burgeoning literature is that not all proteins are the same. In fact, plant proteins, even though they're made up of some of the same amino acids that animal-derived proteins are, don't exert the same effect in the body but particularly on the kidneys, and that's what we're primarily concerned with.

Having said that, I'll just address protein in general. I do think it's important that people not overeat protein. I don't know that we need to restrict protein in all cases other than to promote kidney health, it might be wise to do so. As far as which proteins, in particular, might be associated with uric acid stones, we're looking at two things. We're looking at proteins that can increase the body's production or synthesis of uric acid, but more importantly, actually, for uric acid stones, we're looking at protein food sources that can reduce the urine pH, making it more acidic because that's when uric acid stones will form, that's when uric acid precipitates from urine. To your question about red meat, is that different from poultry or fish? It's not different. They all have the same ability to produce this acid load and lower urine pH. They're not all equal with respect to promoting uric acid biosynthesis.

[Dr. Manoj Monga]
Do eggs decrease the pH too?

[Dr. Kristina Penniston]
It's controversial or you'll find contradictory evidence. The best evidence I think came from Thomas Reamer and his group many years ago now, which showed, and this is contrary to how we might think of it, that egg yolks are actually the acidogenic part of the egg and not the whites. Now that's to me a little bit contradictory because the white is where the protein is, but it turns out, the explanation that I've read, is that it’s the matrix. The matrix of foods is very important, and that's why not all proteins are equal. Even though they might have the same amino acid lineup, the matrix in which they're enveloped, the other constituents of that food, whether it be plant or animal-derived, is important. It turns out that egg whites, even though that's the protein part of the egg, have compounds in them. I don't know what they are offhand, but they have compounds in them that make the whites of the egg not acidogenic like the yolk is.

[Dr. Manoj Monga]
When you mentioned the matrix of food, I understand the collagen and meat can also be lithogenic for a different reason. Is that right?

[Dr. Kristina Penniston]
Yes, you're obviously a reader of current literature. For people who form oxalate stones or who have hyperoxaluria, we used to think very narrowly about what might contribute to that, but now we know that collagen is actually something that I would call an oxalate precursor. There are some amino acids that have this capability as well. What that means is when we eat those foods, collagen for example, it can be used as a substrate for the production of more oxalate in the human body. Of course, oxalate, when it's produced inside the body, has no use that we know of and so it must be excreted. If not excreted, it can be deposited in soft tissue where it can have some serious problems, but when it's excreted in urine, of course, we get hyperoxaluria, which then is capable of forming stones. Collagen is one of those, I'll call it a precursor to oxalate foods, that we see people consuming.

[Dr. Manoj Monga]
Are there specific types of meats or cuts of meats that are higher in collagen?

[Dr. Kristina Penniston]
Yes. I don't know offhand which those are, but I do know that there are. Interestingly, the fattier meats are probably going to have less collagen than some of the less fatty meats, but I'd want to read up on that before I give any definitive advice about that. In general, I would say if you're consistently consuming a moderate amount of meat, by moderate, I mean depending on your body size, maybe six ounces, maybe eight ounces if you're a larger size, maybe four ounces if you're smaller, a day, I don't think there's any concern for collagen, in that sense. I do think there might be a concern for collagen when it comes to the collagen supplements that so many people are taking these days. That has not been very well studied, though I know some people currently studying that are waiting for the results very eagerly.

(6) Dietary Sources of Oxalates

[Dr. Manoj Monga]
Dr. Pennistson, speaking of oxalates, I know you've looked into where oxalates come in the Western diet. What did you find?

[Dr. Kristina Penniston]
Oxalate is mainly found in plant foods, preformed oxalate, I'll say. These oxalate precursors we were just talking about can be found in many foods of animal origin, but oxalate itself, the preformed oxalate, is usually found in plant foods because it is produced by plants to help them maintain homeostasis for calcium. Calcium and oxalate bind in the plant and it allows the plant to store calcium so that in times of deficient calcium, say in the soil, it can liberate that calcium and use it. I think there may also be oxalate in the soil, in bacteria that's a separate thing, so oxalate in the soil. Anyway, plant foods are considered major sources of oxalate, but certain plant foods have a lot more oxalate than others, and the particular ones that people often cite are spinach. Not all leafy greens, but spinach, for sure, has a lot of oxalate in it. Then, some of the potatoes and sweet potatoes, some beans, rhubarb is a strange food that does have a lot of oxalate, and beets is another one.

Practically all fruits and vegetables have a little bit of oxalate, but as far as the super high oxalate foods, those are mainly the ones that I mentioned. Then, some of the whole grains and nuts and seeds. These, of course, are also plant foods, and so they can be very high sources of oxalate as well.

[Dr. Manoj Monga]
Any specific grains, beyond whole grains, that you would say try to minimize or avoid?

[Dr. Kristina Penniston]
Bulgur, for example, is very high in oxalate and most whole grains, that is to say, the unrefined, the whole, the bran, everything in them, most will have quite a lot of oxalate; Soy does, wheat does, wheat berries do. It's pretty much all whole grains. Bulgur, I know, is one of the highest ones. I wouldn't say that people necessarily need to avoid those foods or avoid any food that's high in oxalate. The reason is because we can control the amount of oxalate that our body absorbs, that is absorbed from our gastrointestinal tract.

I don't often tell people that they have to live for the rest of their lives without eating oatmeal or bulgur again or spinach again because of this power that we know of to modify the bioavailability of oxalate. I know oxalate gets a bad rap, and the foods that are high in oxalate get a bad rap, but let's remember that those foods are often coincidentally the highest in magnesium and for fiber and for phytate and antioxidants, all of which can prevent stones.

[Dr. Manoj Monga]
Modulating the absorption of oxalate, what do you recommend?

[Dr. Kristina Penniston]
The bioavailability of nutrients is something that dieticians know very well. We do it all the time. What that simply means is bioavailability is how available something is to you. If it's something you have eaten, then to be bioavailable, it must be absorbed from the gastrointestinal tract so that it can be in circulation in the bloodstream. Dieticians often try to manipulate the bioavailability of things. Usually, we're trying to increase the bioavailability of certain nutrients like iron. For people that need more iron in their foods, we'll tell them you can increase the bioavailability of plant iron, which plant irons are not that well absorbed, but we can better absorb them when we have concurrent consumption of vitamin C or foods that contain vitamin C.

With oxalate, we're trying to do just the opposite. We want to reduce the bioavailability or absorption of oxalate. We do this in a very effective way, which is we advocate the simultaneous consumption of foods or beverages that can contain calcium because when the calcium and the oxalate are consumed at the same time, much of them, not all of them, but they will tend to bind in the gastrointestinal tract just as they do in the urine. When they bind together in the intestinal tract, they form an insoluble complex, a stone, if you will, but you can't absorb it, and so it simply is eliminated in your stool. That's a technique that we can use for people with really high oxalate consumption, whose diets are really probably pretty healthy and we don't want to maybe alter too much. We would simply advocate a good amount of calcium at each eating occasion or meal.

[Dr. Manoj Monga]
What are some of your favorite non-dairy alternatives for that calcium that you need to prevent oxalate absorption?

[Dr. Kristina Penniston]
When I first started practicing clinical dietetics 22 years ago, because I started while I was in grad school, there was hardly anything, and so my patients who were lactose intolerant or had a milk protein allergy had very little to choose from other than calcium supplements. There weren't even as many of those different kinds of formulations as there are now. Everybody knows now that there are many non-dairy sources of calcium, and it's been a real boon for patients with lactose intolerance, for vegetarians and vegans, or just anyone else who wants to avoid dairy.

What I'm talking about is the plethora of plant-based milks that we see in our refrigerated sections of our grocery stores everywhere. We see soy milk, we see rice milk, oat milk, almond milk, cashew milk. There's flax milk. I've seen hemp milk. There's probably others I haven't even bothered to name. There's coconut milk. There are many of these and for too many of them, the manufacturers have added calcium because they realize that they can market it and sell more of the product to people that need calcium, which we all do, but who don't want to get it from dairy. There are also calcium-fortified juices. I know of orange juice and cranberry juice, in particular. There may be others. There are now many more non-dairy calcium sources to choose from than there were before.

(7) Managing Complex Kidney Stone Cases

[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.

(8) Optimal Diet for Kidney Stone Prevention

[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.

[Dr. Manoj Monga]
Dr. Penniston, I'd like to thank you for taking the time to share your expertise. You've given us a lot of food for thought. You've also given us some uncertainties to chew on. Thank you, again, and to our audience, bon appétit.

Podcast Contributors

Dr. Kristina Penniston

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

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 https://www.backtable.com

Disclaimer: The Materials available on BackTable.com 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.