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Transcript

Welcome back to the PKD Dietitian Podcast, I'm Diana Bruen, your host and creator. And if you've been listening to the podcast for a while, you know my goal is to bring you clear, practical, evidence-based nutrition guidance for PKD without the overwhelm and without the BS recommendations online and blasted all over social media. And if this podcast has helped you feel clearer, more confident, or more in control of your nutrition for PKD, there is a meaningful way for you to support the work.

The PKD Dietitian Podcast is now on Patreon, and I've added a few different support tier options for you. In the future, I'll be sharing bonus episodes, extra content, and deeper PKD nutrition insights there as well. If you want to support the show, go ahead and check us out at patreon.com/PKDDietitian.

All right, let's get into today's episode. We know a lot more about PKD than we did 10, even 15 years ago.

We know more about the genes, the pathways, and the drivers of kidney growth and all things related to PKD. One of the areas of research where there has been a lot of interest is looking at how weight loss potentially impacts polycystic kidneys and PKD progression, plus the overall health of someone who has PKD. I get a fair amount of questions from clients and via social media about my thoughts on whether someone would benefit from losing weight if it would "help their PKD".

My answer is, and if you're a long-term podcast listener, you can probably guess by now, it depends. Today, on the PKD Dietitian podcast, we're going to unpack weight loss and PKD a bit more and get into what the research shows or doesn't and how to identify if intentional weight loss is an opportunity that you have to improve your PKD health path. Is there a connection between your weight and PKD kidney health? That's the big question here.

 PKD progression is complicated. You can say that twice and mean it. And it isn't driven by one single thing.

 There are a multitude of factors involved. Nowadays, we understand much more about the genetic mutations that drive PKD, that PKD1 and PKD2. We know about the signaling pathways that are kind of off-kilter and drive cyst growth like vasopressin, mTOR pathway, blood pressure, and inflammation, which all come into play.

 How total kidney volume, which is the size of your kidneys, relates to disease progression. There's also been a growing interest into research into how body weight and how your body uses energy, which is called metabolic health, how they both influence PKD outcomes. Before we jump into what the science shows around weight loss and PKD progression, I want to talk a little bit about something called BMI.

 BMI is the most common tool used for classifying weight status. BMI stands for body mass index, and it's essentially a calculation with categories used to classify us as under, over, or at a healthy weight. To calculate BMI, we use essentially only two things, height and weight.

 BMI doesn't differentiate between if that weight is from muscle or from fat, nor does it take into account how that body weight or any excess fat is distributed. We know if excess weight is distributed in the middle, that is the least favorable. You will often hear this kind of weight pattern referred to as visceral fat.

 With PKD specifically, the weight of your kidneys isn't factored in. It isn't subtracted out. For you folks out there that are working to become active on a transplant list, by the way, your kidney volume and weight is frequently subtracted from your BMI calculations.

 In big studies like the HALT and TEMPO studies, they controlled for this by subtracting kidney weight from someone's BMI, so you can see it does factor in, but isn't always subtracted when it comes to PKD and BMI. The general categories for BMI are as such. If your BMI is less than 18.5, it's considered underweight.

 If it's greater than or equal to 25, it is considered overweight. A BMI that is greater or equal to 30 is obese, and a BMI that is greater than equal to 40 is considered severe obesity, which used to be called morbid obesity. Now, if you're curious about what your BMI is, you can Google BMI calculator and a bunch of options will come up asking for your height, weight.

 I linked one out in the notes for you. If you follow PKD research, you've probably seen publications, some coming out of the PKD Center in Colorado, and larger studies like HALT PKD and CRISP that looked at someone's BMI, their total kidney volume, so their kidney size, and how fast their PKD progressed. I want to highlight right off the bat that this research, most of it primarily focuses on participants who, according to their BMI category, are either overweight or living with obesity.

 More often than not, folks within that quote unquote healthy BMI are not included. This matters when we interpret the results. Looking at these studies, both the small human studies and the larger observational studies, the evidence suggests that a higher BMI, one that categorized someone as overweight or obese, is associated with larger kidney size, faster progression of kidney failure, so that GFR goes down faster.

 Analysis of both of those larger studies, the HALT PKD and CRISP, highlighted association, a clear one showing that higher BMI was associated with hypertension, that high blood pressure, and faster progression, so larger kidneys and lower GFR. But know this, guys, association does not equal causation. This is not proof of a cause and effect because it was only observational.

 However, don't dismiss these results as not relevant. The results, specific to weight measured by BMI and kidney size, showed that overweight individuals, so those with BMI 25 or greater, had a 30% faster kidney growth when compared to folks who were in that healthy weight category. Additionally, folks living with obesity, so with a BMI of 30+, had 50% faster kidney growth.

 And from there, the association that was concluded was that a higher BMI, one that's over 25, was associated with larger kidneys. The conclusion made was that a higher BMI, one that's over 25, was associated with larger kidneys and lower function. Maybe these numbers jump out to you as much as they did to me.

 It is a moment that highlights an opportunity for those of you who may be overweight or living with obesity and have PKD, because here's the good news. These studies also showed with weight loss moving towards a healthy weight, even a reduction of 4% body weight showed an association with slower kidney growth. Those increases, those 30% and those 50% faster growing kidneys, were able to reduce that amount, or dare I say, reverse that from happening.

 But let me be real clear about this. The people who benefited from weight loss were those in the overweight or obese categories to begin with. They did not start at a healthy weight.

 Positive in all of that is that if you are overweight or living with obesity, there is the opportunity to stop that negative impact, to stop that faster growth with a healthy weight loss. I know you hear that even small amounts of weight loss are beneficial when it comes to health and these studies actually showed that losing as little as 4% showed a positive impact. Obesity has a lot of the same pathways that drive PKD.

 I think of it as those pathways essentially going to overdrive with obesity and losing weight and moving towards a healthy weight range helps reduce this in addition to helping to manage better blood pressure and a whole host of other things that come with the disease, the chronic disease of obesity. And why am I telling you this? Because if you're carrying around a fair amount of extra pounds or have obesity, working towards a healthier weight is an opportunity for you. An opportunity and perhaps even some more motivation to help change your PKD health journey.

 Remember, studies showed that even a 4% loss was beneficial in slowing that accelerated kidney growth. The bottom line here is what you eat, how you move, and your lifestyle choices impact progression. And remember, BMI is a screening tool, not a full picture of your health.

 And folks who have PKD that are carrying around excess body weight, improving metabolic health, so how your body uses energy and reducing that excess weight is associated with more favorable kidney outcomes. I hope you found this episode valuable and motivating. Perhaps if you have been wanting to make lifestyle changes to support a healthy weight, a little bit of a kickstart into taking action.

 And as always, happy and healthy eating! 

References 

1. Weight loss and cystic disease progression in autosomal dominant polycystic kidney disease https://pmc.ncbi.nlm.nih.gov/articles/PMC8760407/ 
2. Obesity, Weight Loss, Lifestyle Interventions, and Autosomal Dominant Polycystic Kidney Disease https://pmc.ncbi.nlm.nih.gov/articles/PMC8959086/ 
3. Overweight and Obesity Are Predictors of Progression in Early Autosomal Dominant Polycystic Kidney Disease https://pubmed.ncbi.nlm.nih.gov/29118087/ 
4. Overweight Status, Obesity, and Progression to ESKD in Patients with Autosomal Dominant Polycystic Kidney Disease https://pubmed.ncbi.nlm.nih.gov/39970002/ 
5. Overweight and Obesity and Progression of ADPKD https://pubmed.ncbi.nlm.nih.gov/34117082/ 
6. Weight loss and cystic disease progression in autosomal dominant polycystic kidney disease https://pubmed.ncbi.nlm.nih.gov/35059607/ 
7. Visceral Abdominal Adiposity and Autosomal Dominant Polycystic Kidney Disease Progression: One More Step Toward Identifying Useful Biomarkers and Characterizing the Disease Metabolic Links https://pubmed.ncbi.nlm.nih.gov/39033453/ 
8. Obesity and Kidney Disease: Hidden Consequences of the Epidemic https://pmc.ncbi.nlm.nih.gov/articles/PMC5433675/

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