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A Clinician's Guide to Kidney Stone Prevention: Protein, Collagen & Oxalate Management

Author Olivia Reid covers A Clinician's Guide to Kidney Stone Prevention: Protein, Collagen & Oxalate Management on BackTable Urology

Olivia Reid • Oct 28, 2023 • 530 hits

Clinical dietician Dr. Kristina Penniston delves into the intricate relationship between dietary factors and kidney stone prevention. The discussion highlights the impact of different protein sources, particularly animal proteins, on uric acid stone formation, emphasizing the importance of portion control. Dr. Penniston also addresses the variance in proteins' effects on the kidneys and discusses the matrix of foods, which can alter their impact.

Regarding oxalate, the conversation touches upon its prevalence in plant-based foods and how to control its absorption through the manipulation of bioavailability. Dr. Penniston offers insights into using calcium-rich foods to reduce oxalate absorption. Additionally, the role of collagen as an oxalate precursor is explored and the types of meats and cuts that may contribute to oxalate production. 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

• Protein sources, including red meat, white meat, fish, and eggs, impact uric acid stone formation, with portion control being crucial for prevention. Not all proteins are the same; plant proteins exert different effects on the kidneys compared to animal-derived proteins, emphasizing the importance of understanding protein types.

• Collagen, found in certain meats, can act as an oxalate precursor, contributing to hyperoxaluria and stone formation, necessitating a balanced diet approach for individuals at risk.

• Oxalate, a major contributor to kidney stone formation, is primarily found in plant foods. The bioavailability of oxalate can be controlled through simultaneous consumption of calcium-rich foods.

A Clinician's Guide to Kidney Stone Prevention: Protein, Collagen & Oxalate Management

Table of Contents

(1) Protein Sources in Kidney Stone Prevention: More Than Just Portion Control

(2) Collagen & Oxalate Stones

(3) A Clinical Approach to Oxalate Management

Protein Sources in Kidney Stone Prevention: More Than Just Portion Control

Dr. Penniston explains the intricate relationship between protein consumption and the formation of uric acid stones, shedding light on the distinctions between various protein sources and their effects on kidney health. Beginning with the statement, “not all proteins are created equal”, Dr. Penniston compares and contrasts common protein sources.

Plant proteins, despite sharing some amino acids with animal-derived proteins, differ in their impact on the kidneys, sparking a discussion on the importance of the source of dietary proteins. While emphasizing the significance of not overindulging in protein, the focus shifts to which proteins may be associated with uric acid stones. The key factor to consider is a protein's potential to lower urine pH, making it more acidic and therefore more conducive to uric acid stone formation. Dr. Penniston clarifies that red meat, poultry, and fish all possess this ability, in equal proportions. The discussion also touches on a contradiction surrounding egg consumption, revealing that it's not the egg whites but the yolks that contribute to urine acidification due to their unique matrix, a determinant in the effect of protein.

[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.

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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Collagen & Oxalate Stones

Dr. Penniston discusses the relationship between collagen, dietary choices, and kidney stone formation, explaining that collagen can serve as an oxalate precursor which contributes to the formation of oxalate stones. The discussion highlights that not all proteins are equal, with plant proteins affecting the body differently from animal proteins. While collagen found in moderate meat consumption might not pose a concern, collagen supplements warrant more study.

There is a great need to explore the matrix of food components and their role in stone formation in order to provide valuable insights for clinicians managing patients with kidney stone risks. In terms of oxalate sources specifically, there are many within the Western diet. Emphasizing the prevalence of preformed oxalates in plant-based foods, the discussion underscores the intricate biochemical relationship between calcium and oxalate, emphasizing their significance in plant homeostasis. Spinach, rhubarb, certain potatoes, sweet potatoes, and beets are prominent sources of oxalates, while whole grains, nuts, and seeds also contribute significantly. Dr. Penniston's comprehensive analysis underscores the need for a nuanced understanding of oxalate precursors and their potential impact on kidney stone development.

[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.

[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.

A Clinical Approach to Oxalate Management

Dr. Penniston explains the role of oxalate in kidney stone formation and offers insights into how to modulate oxalate absorption. Contrary to completely avoiding high-oxalate foods, she recommends ingesting foods that neutralize oxalate and prevent its absorption in the gastrointestinal tract. By consuming calcium-rich foods or beverages simultaneously with oxalate-containing foods, a significant portion of oxalate and calcium can bind together, rendering them insoluble and easily eliminated in stool. This is an effective way to reduce oxalate absorption while maintaining a healthy diet. Dr. Penniston also highlights the availability of non-dairy calcium sources, such as plant-based milks, calcium-fortified juices, and supplements, making it easier for patients with dietary restrictions to prevent oxalate-related kidney stones. Understanding the bioavailability of nutrients and its role in kidney stone prevention allows clinicians to tailor dietary recommendations for individuals with varying dietary preferences and restrictions.

[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.

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 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.

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