Kidney stones in their most basic form happen when small crystals of substances like calcium, oxalate, cystine or uric acid are present, typically in the urine, then become stuck in the kidney and increase in size. These substances are generally not harmful unless they are in high amounts, which then leads to kidney stones forming.

Types

The medical term for kidney stones is nephrolithiasis. There are 4 main types:

1. Calcium-based stones
   1. Calcium oxalate
   2. Calcium phosphate
2. Uric acid stones
3. Struvite stones
4. Cystine stones

Calcium oxalate kidney stones are the most common, and account for 80% of kidney stones. Diet is most influential in managing calcium-based and uric acid kidney stones, and will be the focus for the nutrition considerations in this blog post.

In contrast, struvite stones are typically related to bacteria from a urinary tract infection, and cystine stones are related to a genetic disorder where urine contains too much cystine. As a result, these types do not generally have nutrition recommendations.

Kidney stones move through the urinary tract and are passed out through the urine. If they are larger and become stuck in the kidney, however, they can lead to blood in the urine, blocked urine flow, and pain. These kidney stones may need to be surgically removed to prevent declines in kidney function.

Causes

There are also some dietary, genetic, and other medical conditions which can lead to the formation of kidney stones, such as:

Dietary Causes

• Inadequate fluid intake
• Diet with low calcium intake
• Use of supplements such as calcium, collagen, or vitamin C
• Diet with high amounts of animal protein
• Diet high in added sugars
• Diet high in sodium

Genetic and medical causes

• Primary hyperparathyroidism
• Gout
• Diabetes
• Obesity
• Crohn’s disease
• Gastric or intestinal bypass surgery

Stones and PKD

How are kidney stones and PKD related?

Kidney stones may occur in about 25% of those with PKD. It is thought that PKD patients may be predisposed to kidney stone formation due to:

• Kidney cyst formation
• Changes within the structure of the kidney that alter urine flow
• Metabolic disorders (such as low urine pH or higher levels of uric acid) that lead to changes in the urine

The best way to evaluate your risk of developing kidney stones is through a 24-hour urine collection. This simple lab test measures what’s in your urine, including the substances that can cause kidney stones. Your nephrologist or kidney doctor can arrange this test for you.

Strategies

Nutrition strategies for kidney stones and PKD

If you’ve formed a kidney stone in the past, or have a family history of kidney stones, you may be at increased risk of forming kidney stones in the future. Here’s how a 24-hour urine collection can help inform your care:

• The results can help you understand what’s in your urine, and why stones might form
• If you’ve had a kidney stone before, knowing the type of stone is helpful, and a 24-hour urine collection can provide additional details to help tailor your diet to prevent future stones.

Regardless of 24-hour urine collection results, there are some nutrition strategies to minimize kidney stones with PKD. Let’s look at them.

Hydration
With PKD, aiming for 3 litres of fluids per day helps to increase the urine volume and dilute the urine. This helps flush out any tiny crystals that are present in your kidneys, before a stone can be formed. Water should be your beverage of choice, but you could include carbonated or sugar-free options. Aim to keep coffee and caffeinated tea to a maximum of 2 cups per day with kidney stones and PKD.

Sodium
Many individuals with PKD are already managing their sodium intake. This is also important in preventing kidney stones, as too much sodium in the urine can lead to crystals forming. Aiming for a diet around 2300 mg of sodium per day can help with PKD. Some strategies to manage sodium intake are by cooking at home and reducing sodium in cooking; reading food labels and making choices that are 5% daily value of sodium or less per serving; and choosing fresh or unprocessed foods.

Oxalates
Oxalates are a non-nutritive compound found in many foods. Having high levels of oxalate on a 24-hour urine collection can put you at risk of developing calcium-oxalate kidney stones. Reducing oxalate intake can be helpful. Some common oxalate foods can be found in our previous blog on oxalates.

Calcium
Including calcium sources when our meals contain oxolate foods helps decrease the absorption of oxalates. Oxalate and calcium attract each other, so when we eat them together, they will bind in the gut and not the kidneys, decreasing the risk of forming stones. Choose calcium from food sources where possible, rather than calcium from supplements. Some examples include: 1 cup low-fat milk or kefir, ¾ cup regular yogurt, 50 g low-sodium cheese such as mozzarella, Swiss or Jarlsberg.

Protein
Eating large amounts of animal protein may increase the chances of developing kidney stones. When we consume too much animal protein, uric acid levels can rise in the urine. This can lead to uric acid kidney stones forming. The frequency and portion of animal protein is important to consider. With PKD, aim to:

• Choose more plant-based proteins
• Limit animal protein to one meal per day
• Aim for a portion size of about 3-4 oz

Everyone’s diet with PKD may be different. How much protein you need depends on your weight, activity level, kidney function and other health conditions. A dietitian can help you determine how much you may need.

So, what are the key takeaways about kidney stones and PKD?

Consuming a balanced diet and visually portioning your plate to help build your meals can support your overall nutrition with PKD. Filling half your plate with vegetables helps to provide citrate, potassium, and magnesium which are beneficial nutrients to reduce kidney stone risk. Most Canadians do not consume enough vegetables and fruit in their diet. Focusing on adding these foods, along with plant-based proteins, and reducing sodium intake can help to preserve kidney function, prevent kidney stones and manage PKD.

At the end of the day, these strategies incorporate many dietary patterns that have been shown to be beneficial with PKD such as the Mediterranean Diet, DASH diet and low osmolar diet. If you have questions or concerns about your health and nutrition, speak with a dietitian, ask us at the PKD Foundation of Canada, or check out some of our previous nutrition blog and webinar information.

More

• Learn more about oxalates and PKD in this blog post
• Pick up some tips on fluids and PKD here
• Explore sugar and PKD here
• Learn about plant-based diets and PKD here

Recipe

Tofu Fried Rice
Are you looking for a recipe to use up that leftover cooked rice? Look no further. This Tofu Fried Rice comes together in a snap and is packed with flavour. With fried rice, you can use any vegetables you have on hand, so be creative.

Makes 4 Servings

Ingredients

1 TBSP canola oil

1 package (454 g) extra-firm tofu

2 TBSP sesame oil

3 TBSP less-sodium soy sauce

2 TBSP rice vinegar 1 TBSP ground ginger

2 clove garlic, minced

2 cups cooked parboiled, converted, or brown rice

½ cup white onion, chopped

1 cup frozen peas and carrots

2 cup mushrooms, washed and sliced

2 cup Bok choy, washed and chopped

Instructions

1. Drain tofu and wrap in a clean dish towel. Gently press tofu for 1 minute to remove excess liquid.
2. In a small bowl, combine less-sodium soy sauce, rice vinegar, sesame oil, ginger and garlic, and mix to combine. Set aside.
3. Heat 2 TBSP oil in a large skillet or wok on medium heat. When oil is warm, reduce temperature to low and add tofu slices. Cook each side until brown and crispy (about 2 minutes per side).
4. Still on low temperature, add half the sauce to the skillet and spoon over the tofu so it absorbs the marinade. Set aside in a bowl with the liquid.
5. To the same large skillet but on medium heat, add onion, peas, carrots, mushroom and Bok choy. Let cook for 2-5 minutes until tender.
6. Add rice to skillet and cook for 1-2 minutes, stirring continually.
7. Add remaining sauce to skillet, and cook vegetables, rice, and sauce for 1-2 minutes.
8. Serve rice with tofu and green onion on top.

Nutrition Information per serving: 375 calories, 19 g fat, 2.6 g saturated fat, 503.5 mg sodium, 34.3 g carbohydrate, 3.3 g fibre, 20.4 g protein, 525.2 mg potassium, 14.8 mg oxalate, 150.4 mg calcium, 119.4 mg phosphorus

About the author: Emily Campbell, RD CDE MScFN is a Registered Dietitian and Certified Diabetes Educator with a Master’s Degree in Foods and Nutrition. Emily specializes in helping those with kidney disease overcome the confusing world of nutrition to promote health. Emily and her team of dietitians can be found at kidneynutrition.ca.

More

• Interested in another Asian-inspired recipe? Try this Pork Noodle Bowl recipe contributed by PKD patient Kristen Walsh