If you have ever had a kidney stone or have a family history of stones, this article is for you. In one of my many roles, I work as a Dietitian in a kidney stone prevention clinic. Today on the blog, I’m talking about what causes kidney stones and how diet can help prevent them from forming.
Kidney stones are made from crystals that form in your kidney. Approximately 70-80% of all kidney stones are calcium-based. Calcium oxalate is the most common type of stone and can be affected by diet. There are four other types of stones – calcium phosphate, uric acid, cystine and struvite stones. This article will focus on calcium oxalate kidney stones and the role that diet and nutrition play in stone formation.
What causes kidney stones?
- A family history of kidney stones puts one at 2.5 times higher risk for stones
- The prevalence of kidney stones is around 20% in white males and 5-10% in women
- Certain medical conditions such as primary hyperthyroidism, Crohn’s disease, gout, diabetes and renal tubular acidosis can increase the risk of forming calcium-based kidney stones
- Diet affects the development of calcium-based and uric acid stones
How is a kidney stone diagnosed?
Common symptoms of a kidney stone include blood in the urine, a urinary tract infection, abdominal or flank pain. You may be able to pass small stones without difficulty or pain. However, larger stones may require intervention.
To diagnose kidney stones, one or more of these procedures may be done: x-ray, ultrasound and spiral CT scan, 24-hour urine collection and if you have passed a stone – then a stone analysis is done to determine its components.
How can diet help prevent kidney stones?
Let’s dive into the types of foods and fluids to lower your risk of forming kidney stones.
Drink more than 2.5 liters of water per day, ideally with lemon juice added
Drinking lots of fluid is the best way to lower your risk of kidney stones as crystals are less likely to form in urine that is not concentrated and producing extra urine will help eliminate small crystals before they form into larger stones. Aim to drink 2 to 3 liters, which is 8 to 12 cups of fluids each day. Water should make up at least half of the fluid you drink.
The more fluid you drink, the more urine you produce. Increased urine flow flushes the crystals away and reduces the concentration of stone-forming substances in urine. The goal is to produce 2 liters of urine per day – you can check to make sure your urine is pale in colour. Drink more water on hot days, when you are physically active and if you have a fever or diarrhea. Talk to your doctor or dietitian if you’ve been told to restrict fluids.
Adding lemon to your water increases citrate in your urine which will lower your risk of forming kidney stones. Citrate is a compound made from citric acid and citrate binds with calcium in the urine to prevent calcium from sticking to other compounds such as oxalate. The goal is to drink ½ cup of lemon juice per day. You can add ½ cup of lemon juice in 2 Liters of water or 1 Tablespoon of lemon juice per cup of water (for 8 cups). Watch out if you have stomach ulcers and talk to your doctor about alternatives.
Eat less salt, ideally less than 2000 mg (3/4 teaspoon) of sodium per day
If you eat a lot of salt or sodium in foods, the amount of calcium in your urine increases, which increases your risk of forming kidney stones. Limit the sodium in your diet to less than 2000 milligrams per day – that’s ¾ of a teaspoon.
A majority of salt you may eat is from processed foods such as canned and pickled or preserved foods, deli meats and cheeses, frozen meals, soups or broths, and fast food. Read food labels to help you choose foods lower in sodium – foods that have a Daily Value (DV) for sodium of 5% or less are low in sodium.
Avoid eating excessive amounts of animal protein
Eating too much protein from animal foods can lead to high levels of uric acid, high levels of sodium, low levels of citrate in your urine and an acidic urine pH. The protein that affects your kidney stones is from animal flesh, including poultry, red meat, fish, game meats and organ meats. High protein diets (such as the ketogenic diet, Atkins diet or paleolithic diet) are not suitable for people with kidney stones.
Limit meat, fish, poultry and eggs to 2 servings a day. One serving size is 2.5 ounces or 75 grams – this is the size of a 1 deck of cards. Try to choose vegetarian sources of protein instead of meat such as lentils, beans or legumes.
Limit foods high in oxalate and choose low oxalate foods more often
If your oxalate levels are higher than normal, you could benefit from an oxalate restriction in your diet. Oxalate is a compound found naturally in plant foods (fruits, vegetables, grains, nuts and seeds). It is also produced as a waste product by the body and it exits the body through the urine. Oxalate can bind to calcium in the kidney, causing kidney stones to form.
Oxalate is naturally found in very healthy foods. For this reason, it is important to not follow an extremely low oxalate diet. Instead, try to eat high oxalate foods less often, in small portion sizes, with dairy (we will get to that next).
High oxalate foods include rhubarb, spinach, beets, rutabaga, avocado, parsnips, raspberries figs, potatoes, yams, nuts (almonds, peanuts, cashews, hazelnuts), wheat bran, and chocolate (including chocolate bars and cocoa powder used for baking). Use this list to choose lower oxalate alternatives.
Have dairy products with meals
Another way to prevent kidney stones and lower oxalate levels in your urine is to get enough calcium in your diet. Let’s not confuse this with the calcium that ends up in urine (from high salt and high animal protein intake). High dietary calcium intake actually leads to a lower risk of calcium-based kidney stones because calcium and magnesium from dairy bind to oxalate in the gut (and this bound oxalate exits into your stool), which decreases your body’s ability to absorb oxalate. Eating a serving of dairy products with meals can help to lower oxalate levels in your urine.
Some examples of one serving of dairy include 1 cup white milk (not chocolate), ¾ cup yogurt or kefir and 1 oz cheese. If you are lactose intolerant, choose lactose-free dairy products. You can also use dairy products made with sheep milk or goat milk as these are lower in lactose.
Talk to your doctor about any supplements are you taking
Calcium intake from calcium-containing food is recommended over calcium supplements. Avoid taking calcium and vitamin D supplements together as it increases how much calcium is absorbed in your intestines and can increase your risk of kidney stone formation. Talk to your nephrologist (kidney doctor) or dietitian if you are taking a calcium supplement.
Avoid vitamin C supplements (1000 mg) or excess dose in a multivitamin as vitamin C is metabolized into a form of oxalate and increases oxalate in your urine.
This article is not a replacement for seeing a healthcare professional. It is important to see a dietitian or nephrologist who can provide specific recommendations based on your blood and urine results and the type of kidney stone you have.