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Episode Summary
In this episode of the Eat Away Kidney Stones podcast, registered dietitian and kidney stone expert Melanie Betz discusses a recent study published in The Lancet regarding hydration and kidney stone prevention. Melanie addresses the misinterpretation of the study’s findings by some medical professionals and media outlets, emphasizing that water remains crucial for preventing kidney stones. She explains the study’s methodology, which involved a randomized controlled trial with 1,658 participants, and highlights the importance of increasing fluid intake to reduce the concentration of stone-forming molecules in urine. Despite the study’s results showing no significant difference in stone recurrence between the intervention and control groups, Melanie stresses that the intervention group did not significantly increase their water intake. She concludes by reaffirming the importance of hydration in kidney stone prevention and encourages listeners to focus on increasing their fluid intake.
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Hello and welcome to the 143rd episode of the Eat Away Kidney Stones podcast. As always, I’m your host, registered dietitian and kidney stone expert, Melanie Betz.
00:35 Introduction
Today I thought an entire podcast episode would be called for, going over my thoughts in response to a study that came out last month in The Lancet. I’ve seen the results of this study circulating on social media and even via larger news outlets, misrepresenting the findings to say that water isn’t a big deal or isn’t that important for kidney stone prevention.
Spoiler alert: that is not the case. Water and fluid remains kidney stone prevention 101. The fact that I’ve seen multiple medical doctors on Instagram and other social media outlets using the results of this study to prove otherwise is dangerous and irresponsible.
Because it shows that they didn’t actually read the trial and are very unaware of the vast majority of other data that we have that supports the fact that drinking more water is very effective for kidney stone prevention. I won’t go there, but it’s very upsetting to me.
I actually did a response reel to one of the doctors that I saw saying such things on my Instagram and Facebook a couple weeks ago. I’ll link to that if you’re interested in checking it out. But anyway, I wanted to walk through the study so you can decide for yourself what you feel like this is showing, with my interpretation of it, and walk through why water is so important for kidney stone prevention as well.
02:39 Overview of the Study and Its Methodology
Because whenever we see headlines like this, it can shake us and make us question, wait, is this really that important? I want to walk through the study and show you what it actually found and give you the data that you need to make your own decision, as well as walk through the science behind why drinking more fluid is so critical for kidney stone prevention. When you think about it from a high school chemistry standpoint, it really does make sense and it does work.
All right, so the study that was published, and obviously I’ll link to it in the show notes, was published in The Lancet, like I said, and the title of it is Prevention of Urinary Stones with Hydration, a Randomized Controlled Clinical Trial of an Adherence Intervention.
So this is a very big randomized controlled trial, which is exciting because we don’t get a ton of these, especially in nutrition or behavioral health, because there’s not a lot of funding. Medications and prescriptions have a lot more funding behind them. To do actual lifestyle intervention trials like this is really tough because there’s not funding.
Plus, they’re very expensive. It’s not like you can just give someone a pill and say take it every day and go on their way. There are lots of hands involved, lots of different things to think about, especially if we’re talking about changing behavior. It’s really tough.
The fact that this is a randomized controlled trial is very cool because we don’t have a ton of data like this. So this trial randomized around 1,700 people, specifically 1,658 people. All of these people were at least 12 years old and had a history of kidney stones. They were randomized to the control group, which was normal clinical care, or this very intensive behavioral intervention group.
This group had meetings with health coaches. They worked with patients to find reminder systems that would work well for them, such as text messages. They even had financial incentives to help meet those fluid goals. This group was also given specific fluid goals based on their baseline data.
The American Urological Association recommends that everyone with kidney stones consume enough fluid to produce two and a half liters of urine per day. For most people, my blanket recommendation is around 100 fluid ounces per day to meet that goal, though it does vary based on body size, sweating, and diet.
So in the intervention group, people were given very specific fluid recommendations, whereas in the control group they were given general advice to drink more water. The main outcome of this study was kidney stone formation.
06:26 Results of the Study and Misinterpretations
And unfortunately, after two years of this trial, there was no difference in stone recurrence. Nineteen percent of people in the intervention group had a stone event, and twenty percent in the control group.
So this is where a lot of people and reporters have stopped and said, well, water doesn’t matter. But when you actually look at the study, the first question is, did they actually drink more water?
In short, no.
Urine volume, which is a good indicator of how much water you’re drinking, did increase in all groups. That’s not surprising because even the control group was told to drink more water.
At six months, the intervention group did have a higher urine volume, but it was only 240 milliliters higher than the control group. That is one cup of water more. That is not that much more water.
At that time point, their total urine volume was still only about 1.8 liters per day, which is far below the goal of 2.5 liters per day.
By the end of the two years, that difference was even smaller. It appears to have been only about 50 milliliters. So basically nothing.
At the end of two years, the intervention group had about 1.45 to 1.5 liters per day, and the control group was about the same. That is far below our goal.
So this does not say anything about whether water works, because the intervention group barely drank more water. No one was anywhere near meeting the goal.
And the fact that people are taking this and not looking deeper is harmful. Someone with kidney stones is going to read that and think they don’t need to drink more water.
10:55 Why Water Still Matters for Kidney Stone Prevention
So, Even the authors of the trial say that the results do not undermine the importance of increasing fluid intake for stone prevention. It remains a low-cost, low-risk intervention with likely benefits based on previous literature.
There is also a landmark trial from 1996 that showed those who drank more water had fewer kidney stones. The group that drank more water had about a 12 percent recurrence rate, whereas the control group had about a 27 percent recurrence rate.
That is a big difference.
This trial cannot say anything about whether water works because participants did not drink enough more water.
13:06 How Kidney Stones Form (And Why Hydration Works)
Kidney stones are a saturation of stone-forming molecules, most commonly calcium and oxalate.
When the concentration of these materials gets too high, stones form.
From a basic chemistry standpoint, to reduce concentration, you either reduce the number of molecules or increase the volume of fluid. The only way to increase that volume is to drink more fluid.
That is kidney stone prevention 101.
We can also reduce the amount of stone-forming substances in the urine. For many people, that is calcium. For others, it might be oxalate or uric acid.
There are also things we can increase in the urine that make it harder for stones to form, like citrate. When you have more citrate in your urine, it makes it harder for calcium to bind to other molecules.
Urine pH also matters, as do magnesium and phytate.
But the biggest and most effective thing we can do is increase urine volume by drinking more fluid.
That remains true despite this study and how it has been interpreted.
16:10 Conclusion
Now that we’ve cleared that up, I will end this episode of the Eat Away Kidney Stones podcast.
As always, if you have any questions or things you want me to tackle, especially things you see in the news, I would love to hear from you. You can go to kidneystonepodcast.com to submit your question, or you can email [email protected].
I’m always looking for things we can highlight on the podcast, social media, or in my courses.
I hope you have a wonderful week, and I will see you next Wednesday on the Eat Away Kidney Stones podcast.
