Kidney stones are a gathering of mineral and salt deposits that form in different shapes and sizes in the kidneys. Sometimes, they're very painful when they pass through your kidneys and bladder to pass out through your urine.
About 10% of people will have a kidney stone at some point in their life, according to the National Kidney Foundation. Kidney stones are becoming more common in the U.S. because of an increase in sedentary lifestyles, unhealthy diet choices and rising obesity rates, says Dr. Michelle J. Semins, an assistant professor of urologic surgery and director of the Kidney Stone Clinic at UPMC Mercy in Pittsburgh.
Symptoms of Kidney Stones
Some kidney stones have symptoms, while others don't. Symptoms associated with kidney stones include:
- Pain on the side or back of the body.
- Cloudy urine.
- Urine that changes colors and may be an unusual color, such as pink or brown.
- Feeling a need to urinate, but being able to urinate only a small amount.
- Having a fever. This may happen if an infection develops with the kidney stone.
Many people will pass a kidney stone and not even know it. For mild pain from a kidney stone, you may have to take an over-the-counter pain reliever and wait until you pass it. However, if your pain can't be controlled or if you have a fever or your urine changes color, let your doctor know.
More severe pain could indicate the stone is blocking the passageway from your kidney to bladder. This type of stone may need to be treated with the use of shock waves aimed toward the kidney to break up the stone into very small pieces, says Dr. Matthew R. Weir, a professor of medicine at the University of Maryland School of Medicine and head of the division of nephrology at the University of Maryland Medical Center in Baltimore. This type of procedure is called extracorporeal shock wave lithotripsy.
Not all kidney stones are alike, and neither are the causes behind them. However, the cause of many kidney stones is connected to what you eat or drink. Here's more information on how kidney stones form and what foods or beverages you should include in your diet – or avoid – if you have kidney stones.
Different Types of Kidney Stones and Their Causes
There are four types of kidney stones:
- Calcium oxalate stones.
- Uric acid stones.
- Struvite stones.
- Cystine stones.
Calcium oxalate stones. This type of stone forms when calcium combines with oxalate in your urine. Oxalate is a substance found in many foods, particularly in plant-based foods. Eighty percent of kidney stones are formed by calcium oxalate. Causes of calcium oxalate stones include a diet high in oxalate and not consuming enough calcium or fluid.
Uric acid stones. This type of stone occurs when your urine is too acidic. For instance, you may have lost fluid due to dehydration or diarrhea, says registered dietitian Kimberly Barton of Bair Aesthetics in Columbus, Ohio. A diet that is high in protein also may lead to uric acid stones. Uric acid stones make up about 9% of the stones that occur in people, Semins says.
Struvite stones. These stones are commonly linked to urinary tract infections. They form when ammonia builds up in your urine.
Cystine stones. This is the least common type of kidney stone, and it's formed by a genetic disorder called cystinuria. A person with cystinuria leaks a substance called cystine in their urine. When there's too much cystine, it can lead to the formation of kidney stones. An estimated 1 in 7,000 people have cystinuria.
Kidney stones also can be associated with the use of certain medications, infections and medical conditions such as inflammatory bowel disease.
Kidney Stones: Foods to Eat and Foods to Avoid
Once you've had a kidney stone, there's about a 50% chance that you'll have one again within 5 to 10 years if you don't do anything to try and prevent them, Semins says. The type of stone you have determines what foods or drinks you should consume or avoid to reduce your risk of getting another kidney stone.
This is why if you pass a kidney stone at home, you should try and collect it and bring it to your doctor. He or she can analyze it to let you know what type of stone it is. That can help you make changes to prevent it from occurring again, Weir says.
The causes of struvite and cystine stones are not as closely linked to what you eat as calcium oxalate and uric acid stones. However, people with all types of stones can benefit from some general dietary recommendations:
1. Hydrate. Adequate fluid intake helps when you are prone to kidney stones, says Debbie Petitpain, a registered dietitian in Charleston, South Carolina, and a media spokesperson for the Academy of Nutrition and Dietetics.
Fluid can help block the buildup of the substances that form stones. Drinking more fluid also can make it easier to pass a stone if one develops. The good news is that you don't need to stick only with water. Milk, juice, coffee and even soda can count toward your fluid intake. Of course, it's better to avoid soda due to its high sugar content, Petitpain says.
The best way to judge if you're getting enough fluid is by looking at the color of your urine. "Your urine should look like pale lemonade, not dark like apple juice," Petitpain advises. For some people prone to kidney stones, this could mean consuming as many as 100 ounces of fluid a day.
2. Cut your salt intake. Too much sodium can increase calcium in your urine, and that can contribute to stone formation. When evaluating your salt intake, think beyond just the salt shaker – processed foods often have a lot of salt. Look for no-salt, low-salt or heart-healthy options, Barton advises. The current sodium recommendation for adults is no more than 2,300 mg daily, although the American Heart Association reports that most Americans consume 3,400 mg each day.
3. Eat less food in general. Most Americans consume too many calories. By eating less, you'll have the dual effect of eating fewer calories and consuming less salt, Petitpain says.
4. Aim for one or two dietary changes at a time. Semins doesn't like to overwhelm patients by giving them a long list of foods to avoid. Instead, she'll give them one to two specific changes to make. This helps make changes less overwhelming and increases the chance that they can follow recommendations.
5. Think long term with your dietary changes. You'll probably need to follow kidney stone-related food recommendations the rest of your life. "It's not something that happens once and goes away. If you're predisposed to stones, they'll show up again more likely than not," Weir says.
Foods to Eat and Avoid for Specific Types of Stones
In addition to the recommendations above, here is some more specific guidance for foods to eat or avoid depending on the type of stone you had.
Calcium Oxalate Stones
Avoid or cut down on eating foods that are high in oxalate. This includes:
- Beets.
- Chocolate.
- Nuts.
- Nut butters.
- Rhubarb.
- Spinach.
Look for ways to make gradual changes, For example, replace your spinach salad with a mixed green salad that just has a little spinach, Semins suggests.
Check with your doctor before using a vitamin C supplement. Many people are interested in vitamin C to protect their immune system. However, too much vitamin C can break down into oxalate, go from the kidneys and into the urine and potentially form stones. An effective way to get vitamin C instead of supplements is by adding a splash of squeezed lemon to your water, Petitpain says.
Aim to eat about 300 mg of calcium with each meal. If you're prone to calcium oxalate stones, you actually shouldn't avoid calcium. You need it in your diet so it binds with oxalate and can be removed from your body. "Calcium binds to oxalate in the GI tract and gets removed in the stool," Barton says. If you're prone to oxalate stones, this is one way to avoid that oxalate buildup.
Two calcium sources that Petitpain recommends are yogurt and kefir, as they both are high in calcium. One 8-ounce serving of plain yogurt has 415 mg of calcium, or 32% of the recommended daily value. Kefir, a fermented yogurt-type drink, has a similar amount. Yogurt and kefir also provide healthy bacteria to the gut, and that can help break down the salts that turn into kidney stones.
Your body needs to have that right balance of calcium to help prevent kidney stones – not too much and not too little. Although eating calcium-rich food with meals is useful, check with your doctor or registered dietitian before adding a calcium supplement to your diet. An excess of calcium could also lead to stone formation. If you're using a calcium supplement, you could increase your chances of getting too much of this mineral.
Uric Acid Stones
Eat organ meats and wild game no more than once a week. These types of meats are high in purine, a substance that contributes to higher uric acid production. Certain seafoods, such as sardines, herring and anchovies, also are high in purine, Barton says.
Decrease your overall meat consumption. This is because a high-protein diet is associated with uric acid stones. Try to designate certain days of the week as non-meat days. When you do eat meat, limit your portion to no more than one-fourth of your plate, Barton advises.
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