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

[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]
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.