They are tiny terrors that stealthily lie in wait until striking, often without warning. They’re kidney stones — crystalline nuggets that grow in our kidneys, sometimes getting painfully stuck as we try to expel them in our urine.
The symptoms vary. Some people pass stones without even realizing it; others feel an increased urgency to urinate, have blood in their urine, or feel pain in the back or groin that can range from mild to excruciating, says Ivan Porter, M.D., a nephrology specialist in Jacksonville, Florida, with the Mayo School of Graduate Medical Education.
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Whatever the symptoms, kidney stones are surprisingly common. About 11 percent of men and 6 percent of women get them, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Genetics can make a person more prone to these benign-looking clumps, as can certain medications (like diuretics and calcium-based antacids) and jobs (truck drivers, teachers and others who aren’t able to hydrate often enough). But diet can play a role, too.
If you’ve had a kidney stone, your doctor may recommend tweaks to your diet based on the type you had (there are four: calcium stones, uric acid stones, struvite stones and cystine stones). After all, the risk of recurrent stones is substantial, but changing what you eat may prevent them from coming back.
With that in mind, here are eight dietary changes that may help you avoid them.
1. Drink lots of water
“Water is usually our best and first line of defense against kidney stones,” Porter says. Aim for 60 to 80 ounces of water a day to start, knowing that “you may end up needing more than that, depending on your risk profile,” he adds.
The American Urological Association recommends that urine volume be at least two and a half liters a day, points out Paul Palevsky, M.D., professor of medicine at the University of Pittsburgh School of Medicine and president of the National Kidney Foundation. Not sure how to measure that? Porter has a simple guideline: Your urine should be clear, not yellow, orange or brown.
2. Cut down on processed and other high-salt foods
“If someone has high calcium in their urine, you want to make sure they moderate their sodium intake,” Palevsky says, since a high level of salt “increases calcium excretion in the urine.”
Limit processed foods such as crackers, chips, and frozen and pre-made meals, which are loaded with the stuff. Current U.S. Dietary Guidelines recommend that Americans consume less than 2,300 milligrams (mg) of sodium per day. Most, however, take in significantly more than that — to the tune of 3,400 mg, according to the Food and Drug Administration.
3. Make milk, cheese or yogurt — but not calcium supplements — part of your diet
It may seem counterintuitive to eat foods filled with calcium to avoid calcium stones — the most common type of kidney stones — but “dietary calcium is actually good,” Porter says. In fact, it can help block other substances in the digestive tract that can cause stones, according to the NIDDK. Your health care provider can help you choose the best calcium-rich foods for your situation.
Calcium supplements, on the other hand, “can increase our risk of stones,” says Porter. Other supplements you may want to cut down on include vitamin D, which helps the body absorb calcium, and vitamin C, which is converted into oxalates (risky if you are prone to calcium oxalate stones).
“In the past, people would be put on very low-calcium diets, but that resulted in an increased risk of osteoporosis,” Palevsky says. “So you don’t want to really, really restrict calcium intake; the goal would be 1,000 to 1,200 mg of calcium per day.”
4. Add lemon and lime juice to your drinks
Why? Because they contain citrate, “a natural stone inhibitor,” Porter says. “It chelates calcium, which means it prevents calcium from bonding with something else.” Some doctors prescribe potassium citrate as a pill to lower kidney stone risk.
5. Eat plenty of fruit
In general, fruits are good at helping with kidney stones because they have a high water and fiber content, offer high levels of magnesium and citrate, and are more alkaline — all of which help fight kidney stones. (For some patients, Porter prescribes a magnesium oxide supplement to prevent stones.)
6. Take care when eating leafy green vegetables, rhubarb, beets and sweet potatoes
Yes, those veggies are part of a heart-healthy diet, but they are also high in oxalates, a naturally occurring compound linked to kidney stone formation. There is a workaround, however. “One strategy is to make sure you’re having a low-fat dairy serving at the same time you’re having a high-oxalate food,” Porter says, “because the dairy will provide calcium, which will bind with the oxalate and stay in the stool, not be absorbed into the blood and put into the urine.”
7. Cut back on animal protein
“If someone has uric acid stones or calcium stones and relatively high uric acid in the urine, they may want to limit the intake of nondairy animal protein,” Palevsky says. That’s because animal proteins have high levels of compounds called purines, which can cause you to excrete more uric acid and be more prone to uric acid stones. Porter recommends limiting your protein intake to 6 ounces a day. “And lean meats are better than fatty meats,” he adds. “When we eat fatty foods, we have a response in the intestine that makes us absorb more oxalate.”
8. Limit your iced tea, sodas, and soy or almond milk
A 2012 study out of Loyola University’s School of Medicine found that drinking lots of iced tea can contribute to kidney stones, because tea is high in oxalate. Colas are also a no-no. “Colas, especially dark colas, are made bubbly by phosphoric acid, and that increases the risk of kidney stones,” Porter says.
Pale sodas like ginger ale are better options, he adds, but beware their high sugar content. Sugars increase the amount of calcium in the urine and lead to metabolic syndrome, bad cholesterol and diabetes, all of which tend to cause more acidic environments in the body. As for dairy substitutes like almond and soy milk? They, too, are high in oxalates.
There may be good news for coffee drinkers, though. A Swedish-based observational study published in October in the American Journal of Kidney Diseases looked at data from 571,657 people who had kidney stones and found a link between increased coffee intake and reduced kidney stone risk.