Episode 52 • December 2, 2025

Fact or Fiction?

Stop Eating Carbs if You Have PKD

Transcript

Welcome back to the PKD Dietitian Podcast. I'm Diana Bruen, creator and host and boy do I have a good episode for you today. Recently I was asked, do I need to stop eating carbs since I have PKD? Am I making my cyst grow faster when I eat something starchy or sweet? Folks, this wasn't the first time I have been asked questions like this about carbs and it for sure won't be the last.

The answer is, it's complicated. But you know what? It doesn't have to be. In today's episode we are going to dig into carbs and PKD so you no longer need to be confused because food is complex.

And what I mean by this is that the whole foods we eat are made up of more than one single nutrient. The whole matrix of what is in different foods, that's everything that's in them, how we digest and absorb them, it matters. And it does matter when it comes to carbs and PKD.

Even though we are going to zoom way in and look specifically at carbs today, at the end we are going to zoom right back out and look at the big picture. Because that matters. You aren't eating a single nutrient in isolation and I don't want you to forget that.

Carbohydrates have gotten a pretty bad rap over the last several years and have been singled out as a driving force in weight gain, disease, and obesity. The truth is there are different types of carbohydrates and unfortunately they have all gotten lumped in under the umbrella of carbs equal bad. Not all carbs are quote-unquote bad even though that is how they have been portrayed.

They have been portrayed as poison for PKD. The reality is is that the source and type of carb matter. Some are much better like the natural carbs and whole foods like an apple than others like the processed and added carbs aka sugar in a soda.

In order to better understand any potential impact of dietary carb intake and your PKD and its progression, let's step back now and look at what a carbohydrate is plus the different type of carbs and review if there are good versus bad carbs. We're going to look at what the science shows around PKD and carbs and of course we're going to bring it back to what does it all mean for you. Plus I'm going to leave you with some action steps to take.

You'll check in with your carb quality intake and even some positive changes you can make for PKD. So what exactly is a carbohydrate? Carbohydrates are what is called a macronutrient. This is just a nutrient in food that we eat in larger amounts that provides energy.

A carbohydrate simply put is a molecule made up of chains of different types of sugar. We are talking about molecules here, not the white sugar you buy at the store and use for baking, but short and longer chained molecules. One thing you need to know is that all the food we eat that contains digestible carbs, those carbs get broken down into glucose in our bodies.

Glucose goes by several different names. You've probably heard it referred to as blood glucose or blood sugar, different names for the same thing. I am going to try to stick to calling it glucose to make everything a bit less confusing.

I want you to think of glucose as energy. It's one of two energy sources that your body is able to use. When we look at types of carbs, because they're different types, there are three main types and each has a different chemical structure.

Those three types of carbohydrates are sugar, starch, and fiber. Each of those three types is also categorized as being either a simple carb, so this is a short chain of sugar, so it's really like one to two molecules, or a complex carb. These are much longer chains of molecules.

Let's look at each of those different types and see how they differ. Sugar is a simple carb. Like I said, it's made up of one to two sugar molecules.

Now, sugar itself occurs both naturally in foods and is also added to foods. Naturally occurring sugar is in stuff like fruit and dairy and even some vegetables. The added sugars is in processed foods like soda, candy, yogurt, coffee drinks, just some examples.

These are pretty obvious examples, but sugar is added to many food-like products on your grocery shelves. What is the difference between these two? Naturally occurring sugars, like the one in an apple, aren't present as a standalone sugar. That whole apple also contains vitamins and minerals and fiber and phytonutrients, which are just plant nutrients.

All of these have perks for PKD and make up the whole matrix of that apple. Added sugar doesn't come with any of that. It's essentially a standalone sugar.

Some people like to call it empty calories. That's empty energy. Energy that requires very little work to access or to digest.

Because of that, it can add up pretty quickly to an influx of glucose. When we are eating added sugars often or foods that contain them frequently, that added glucose, remember it's energy, adds up to stored energy, which is weight gain. The second type of carbohydrate is a starch.

Starches, like the ones found in whole grains, beans, and some veggies like peas, potatoes, and corn are categorized as a complex carb and they are much longer chain molecules. For starches, what it really comes down to is how processed that starch is. Whole foods with naturally occurring ingredients, usually whole grains, that are processed are refined carbs.

I want you to think of removed when it comes to refined carbs. Refined carbs are made by stripping away all those naturally occurring ingredients, those nutrients, including fiber. They are processed down into a much simpler carb that is quickly digested.

The parts that make those starches and grains complex are removed. I think of refined carbs as essentially the white starches. Those white starches are white bread, pasta and rice, and even flour, pizza dough, many breakfast cereals, and sugary sweets.

These are the carbs that offer very little when it comes to nutritional value. What they do offer is easy access to glucose energy, and folks, this isn't necessarily a good thing. A dietary pattern that is heavy in added sugars and those refined carbs, which I often find myself calling crappy carbs, catch up with you.

These are the carbs you want to have in a limited amount. I've gotten in the habit of referring to overly processed food where they're fine carbs and added sugar as crappy carbs, and whether this is a good or bad thing is yet to be determined, but it gets the point across. What I don't mean is that you can never have a slice of that birthday or wedding cake, or that you need to avoid pizza for the rest of your life.

What I mean is that make these the occasional. Make them the once in a while, not the every day, every week, every meal choice. Big picture here, folks.

Big picture. You aren't going to make your kidneys bigger or your cysts grow faster by partaking in that once a year homemade gingerbread cookie your grandma bakes. It is what you do that is day-to-day and consistent that matters more.

I often work with clients to, quote-unquote, clean up their crappy carbs, and what that means is we're moving towards more whole food eating and cooking with a focus on foods that they both enjoy and that have perks for PKD. The third type of carb and last is fiber. Fiber is plant roughage.

It's a complex carb and your body doesn't digest it. We just, as humans, don't have the enzyme to break it down, and because we don't break fiber down during digestion, it doesn't contribute any glucose. Oh, but don't take that to mean that fiber isn't an important carb.

Not only does it keep you moving and regular, it's also food for your guts bacteria. Hello, prebiotic fiber, and it's connected with lots of perks for PKD, gut health, and heart health too. I want you to hear me when I say this.

Naturally occurring carbs, those in whole foods, do not drive cyst growth and PKD progression. It is really the refined carbs, the added sugar, that will add up and are associated with likely creating faster progression. Before I break that down, I want to share with you how to look at a nutrition label so you can identify naturally occurring carbs versus added sugar.

You'll be able to tell if a product you're getting is a good option or an occasional choice. If you're somewhere where you can safely access a food label, pause the pod and go grab it. On that nutrition label, if you are in the United States, four things are listed for carbohydrates.

First up, you'll see total carbohydrates. This is the sum of all of the three different types of carbs, the sugar, the starch, and the fiber. It's nice to know, but underneath that is where it gets interesting.

It breaks it into the different types. You'll see dietary fiber. Generally, the more the better.

You'll also see total sugars. This includes both those naturally occurring sugars and the added. What is really worth looking at is underneath that, and it says included added sugars.

This is the addition of sugar, and you want this as low as possible, preferably zero. Now that you know the three types of carbs, sugar, starch, and fiber, I want to briefly touch on how we digest them. During digestion, all the starches and carbs from the foods we eat, like I said, are broken into glucose.

That glucose is absorbed from your GI, your gut, into your bloodstream, where it is shuttled into your body's tissues and cells by insulin. A very small amount is stored in your liver, and if there is extra or excess, well, it gets stored elsewhere in your body because it isn't immediately being used. How fast this happens and how much glucose ends up in your blood depends on the food itself, that whole matrix of that food.

Simple carbs, those standalone ones like added sugar, white flour, and refined starches, those get broken down pretty darn quickly. Being already, quote unquote, processed makes it easy for your body to access that glucose energy. Because of that, glucose from them is released quickly, sometimes very quickly.

Folks, the standalone simple carbs and those refined starches, those ones that have all the good stuff removed, are the ones that can spike your glucose, and when you eat them on the regular or in excess, very much contribute to weight gain and stored body fat. If your dietary pattern is high in these carbs, that's also linked to a higher risk of diabetes, heart disease, even elevated triglycerides and cholesterol. Complex carbs and starches like those ones in whole grains and veggies and beans and fruit, those take much longer to digest than those standalone simple carbs.

Your body actually has to work for that glucose from these naturally occurring carbs. And know this, with whole foods, you really aren't going to find sugar or simple carbs by themselves. They are always part of that bigger food matrix.

When it comes to carbs and PKD, the more complex, the better. Let me give you an example here. Let's look at that apple versus a soda.

I know what you're thinking. There is an obvious difference between these two, and you're correct. But that soda could very well be an apple drink or a juice from concentrate, because they both generally have added sugar.

I am using soda because, well, it is that obvious. So what do an apple and a non-diet soda have in common? They both contain fructose, a simple sugar. An apple naturally contains simple carbs.

It's that fructose. But remember, you can't look at the whole food as just parts. One medium apple provides about 95 calories, about 25 grams of total carbs.

Now, underneath that, you got 4 grams of fiber, 19 grams of sugar, that fructose, but that's including 0 grams of added sugar. Now, let's look at that 8 ounces of soda, so 1 cup of soda. It's got 190 calories, 52 grams of total carbs, and underneath that, it's got no fiber and 52 grams of added sugar.

That added sugar is high fructose corn syrup. When you eat that apple, that simple sugar naturally contains fructose doesn't immediately get broken down into glucose because it's not a standalone sugar. Your body doesn't have easy access to the carb.

Whereas when you drink that soda, which also contains fructose, your body's got easy access to it. Not only that, but that is a lot of sugar. This, folks, is a standalone sugar.

Very little needs to be done by your body to digest it, to get to that glucose. That high fructose corn syrup is concentrated, easy to digest, and ends up in your blood as glucose quite quickly. Are you starting to get the big picture difference when it comes to carbs? How the carbs are packaged and their whole nutritional value is the big picture that needs to be considered when it comes to how they can impact your PKD health and progression.

Let's bring it back to PKD now and the big question of the day. Do carbs matter for PKD? Does eating carbs make PKD progress faster? Do they, quote unquote, feed larger kidneys? My choice of wording there was 100% intentional. Here's what we know about PKD and its energy source.

PKD cis cells have a different metabolism than any other part of your kidney. This just means that they use energy differently. Those cis cells, the ones that are mutated because of PKD, can only use glucose for energy.

That energy is what they use to multiply and grow, which, of course, is what we ultimately want to slow and stop. Here is what science has shown us around energy and glucose and PKD. Two things consistently linked with faster PKD progression with having larger kidneys and a faster decline in kidney function that EGFR are, number one, type 2 diabetes, and number two, being overweight or obese.

What do both of these conditions have in common? An excess of glucose. It often comes from diets high in added sugar and refined processed carbs. A diet high in added sugar and those refined processed carbs increases the risk of weight gain, obesity, and type 2 diabetes.

Carrying excess weight, especially being obese, is strongly and independently associated with faster progression of ADPKD. Now, this isn't about one cookie or that one slice of birthday cake. It's the long-term dietary pattern that is high in added sugar, lots of refined carbs, lots of excess calories.

That's what drives the risk. PKD and the impact of obesity and diabetes is much more complicated than having an influx of all that extra glucose, quote-unquote, feeding cyst cells. Inflammation, higher blood pressure, and vascular issues are some of the other contributors to faster progression, but glucose in excess is 100% a factor, and that excess rarely comes from whole foods which contain quality carbs.

I suspect it is difficult to gain a ton of weight eating apples and broccoli. I'm just saying. It's the refined carbs, the processed carbs, the easy-to-overeat carbs that are nutritionally stripped and are the ones that add up quickly.

This is a simplified explanation. There are more PKD growth pathways involved, but here's one important piece of the puzzle. When there is too much glucose coming in, and too often, and more than the body needs, that glucose gets stored, and it gets stored as body fat, and that's what contributes to weight gain.

It also increases insulin resistance and can raise blood glucose over time. This is essentially a constant influx of glucose, a constant influx of an energy source. All of these become part of the cycle that's particularly problematic for PKD.

I want to make an important point. Added sugar and ultra-processed carbs do not directly cause diabetes, but a diet high in them promotes obesity and insulin resistance, and both are major risk factors for type 2 diabetes. Like I said, this becomes a bit of a vicious cycle.

A dietary pattern for PKD, one that's more refined carbs, one that's got a ton of added sugar, equals more glucose, which equals more of an energy source, more fat storage, more insulin resistance, higher blood glucose, and all of this is also associated with stronger drivers of cyst growth. And by the way, I always think PKD cysts love that influx of constant glucose, and I think of them essentially glucose addicts or sugar addicts. Let's zoom back out now and look at what this means for you, plus some actions you can take today.

When I'm working with clients, I'd like to look at three different opportunity options when it comes to carbs, which we work on depends 100% on that person, their life, what their current diet looks like, and what their goals and other opportunities are. This is something we dive into in our first initial session, just really outlining all the opportunities they have to positively impact their PKD and kidney health. Here are the basic three opportunity options that I see around carbs.

The first is clean up the crappy carbs. This is for someone who needs to shift towards more whole foods, possibly lose some weight. They want to reduce added sugar and their intake of refined carbs.

We explore where the added sugar is sneaking in. We work on retraining their taste buds to not crave that super sweet and creating patterns where they're cleaning up the crappy carbs. The second opportunity is to focus on healthy PKD diet, to add in perks for PKD and who this is for.

These are my folks that come in and they're generally eating a really good diet, albeit a limited diet. They're sticking to like 10 foods that they know are safe. They're scared of carbs, but ketogenic therapy is not necessarily for them at this time.

What we focus on is intentionally adding in those whole food carbs with perks for PKD, adding food back in and their other opportunities. The last opportunity option is ketogenic therapy. This is the most aggressive nutrition therapy we have for PKD.

It's where we switch over from running on glucose for energy to running on that second source that I mentioned earlier, which is ketones, little energy nuggets. Keto isn't for everyone and I don't recommend it across the board for everybody. With keto, what we do is we reduce the net carbs eaten and switch over to using fat for fuel, using ketones.

This will be the primary energy source, dramatically reducing that glucose energy source. What you need to know about ketogenic therapy is we don't reduce carbs because they're inherently bad. That is not the goal.

The goal is to shift the energy source the body uses to not glucose, so we don't have that constant influx of glucose as the primary energy source. We pick whole, healthful food sources that are naturally higher in fiber, also like broccoli for the carbs. Remember, fiber isn't digested and broken down into glucose, so ketogenic therapy for PKD is a nice high fiber diet.

It's not how low can you go with carbs. It's all about balance and nutrient dense and delish food. By the way, the Keto Mastery Program, which is my 16-week group program, is starting up in January.

This is for you if you want to do the most aggressive nutrition therapy for PKD and want to learn and live kidney safe and PKD focused keto. I will drop the link in the show notes. Go check it out.

It's an amazing and supportive small group program. You can even claim a spot ASAP if you are all in, or jump on my wait list to learn more about the Keto Mastery Program, or KMP as I often call it, to see how it can support you and if it's just what you are looking for. If you aren't following a ketogenic lifestyle or planning on working with a professional to start keto, both are 100% okay by the way.

Keto is an opportunity we have for PKD, but not the only one. So I want to highlight these other two areas to check in with to see how you are doing or what opportunities you have to improve your diet for slower PKD progression and for PKD health. Number one, check in with your added sugar.

You can track one day or a few or a week. I really like Cronometer because you can check off added sugar. It doesn't capture everything, but it gets you a really good idea.

By tracking, you'll get a good idea of how much you have coming in, and I guarantee it's probably more than you suspect. Start here. Find out how much you have coming in generally on a day-to-day basis based on how much you have set a goal for what you would like to reduce it to, and make this a realistic goal.

How you can do that is look at the labels in your cupboard. See where sneaky sugar sources are. Look at the package of prepared food you eat regularly.

Do they have added sugar? For those of you who like numbers, a good quote-unquote ultimate goal is around 25 grams or less a day. Guys, this is like six teaspoons of sugar. It's a fair amount.

The second area to check in is, what are my biggest sources of refined carbs? Again, go back and look at your pantry. Look at your prepared and processed food. Check in, and yes, folks, this includes the ultra-processed foods that are made with those refined carbs.

What you want to do is see, okay, what are my main sources? Can I swap them out? Can I cut them out? Do I have better options? Your next step, once you have looked at your added sugar and or your refined carbs, is to add more whole foods back in. Can you swap out those sugar sweetened stuff? For example, yogurt. The yogurt aisle is essentially a dessert aisle.

Look at how much added sugar is in your yogurt. Swap out that sweetened yogurt for a no added sugar option. You can add your own fruit.

You can add your own stuff. Those refined carbs, can you swap them out for a whole food or a whole grain? These are steps you can take. Focus on whole foods, the stuff that doesn't come with a nutrition label and is as close to how it was originally grown.

Notice it may take time to transition. Diet and lifestyle changes are hard. Like I said, set a realistic goal, hit that goal, and then move towards the next phase of your PKD diet goal.

Two words I used a lot today are naturally occurring and in excess, because this is what it boils down to. Naturally occurring carbs, these are the whole food healthy carbs. You don't need to limit them or fear them.

In excess, these are the ones that tend to be the standalone sugars, the refined carbs. These are the ones that will add up to weight gain, add up to excess energy, and the ones that potentially will impact your PKD progression negatively. When it comes down to carbs, it's the refined carbohydrates and processed foods that are the crappy carbs.

They're quickly digested, heavy with simple carbs, and your body doesn't have to work very hard to access that glucose. They are often heavy on the calories. Instead of asking how much when it comes to your carbohydrates, a better question is to ask, what is the quality of my carbs? Are they from whole foods, from added sugar, and are they super processed? I hope this episode helped clear up the carb confusion for you.

Resources

The Keto Mastery Program: https://www.thepkddietitian.com/ketomasteryprogram
Blog: https://www.thepkddietitian.com/blog/sugarandPKD

References

Connect With Me

Follow me on Instagram @the.pkd.dietitian
Send me an email, ask a question, request a podcast topic: [email protected]
PKD Connect Call: https://p.bttr.to/3yDTdkE (This is the first step in working together!)

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