Know Your Stones...Protect Your Kidneys

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Know Your Stones...Protect Your Kidneys

Author: Betty Kovacs, MS, RD
Medical Editor: William C. Shiel Jr., MD, FACP, FACR

Do you know your kidney stone?

The unfortunate thing about kidney stones is that once you have had one there is a significant chance that you will have another one. Fortunately, there are things that you can do that may help prevent future occurrences.

One of the keys to prevention is to learn about your previous kidney stones. If you pass a stone and can save it, your doctor can have it analyzed to determine precisely what kind of stone it was. Your doctor may order blood and urine tests as well. The tests will be checking your urine volume and levels of acidity, calcium, oxalate, sodium, citrate, creatinine, and uric acid. Knowing what caused your stone will make preventing future stones more likely.

How can your diet increase the risk for calcium stones?

Approximately four out of five kidney stones are calcium stones. These stones are often a combination of calcium and oxalate, but can also be a combination of calcium and phosphate or a combination of all three. A great deal of research has uncovered dietary factors that can lead to the development of these stones.

The beef about animal protein: Protein is an essential nutrient needed for numerous functions in our body. The average American consumes about twice the RDA for protein each day with the majority of it coming from animal sources. Some research has shown a link between kidney stones and diets high in animal protein, while others have found no difference in stone formation in animal versus plant protein consumption. If the majority of your meals contain a source of meat (for example, chicken, turkey, eggs, beef, seafood, pork, or dairy foods), then the recommendation would be to cut back on the quantity and/or frequency that these are consumed. Here are some ways to get protein from plant sources:

  • Soy cheese
  • Tofu
  • Beans
  • Chic peas
  • Lentils
  • Soy milk
  • Whole grains
  • Vegetables
  • Nuts (if oxalates are not a problem)

Quick GuideKidney Stones: Symptoms, Causes, and Treatment

Kidney Stones: Symptoms, Causes, and Treatment

Shake off the salt. Research is clear on the fact that the sodium found in salt can cause problems by increasing the amount of calcium that you excrete in your urine, which in turn increases your risk of another kidney stone developing. The recommendation is to consume a maximum of 2,000 to 3,000 milligrams (mg) of sodium a day. The main source of sodium in our diets comes from processed and prepared foods. The sodium is used as a preservative and taste enhancer in foods such as canned foods, frozen foods, and cold cuts. Many of these products are now available in low-sodium versions, so be sure to read the label. The food label guidelines for sodium are as follows:

  • Sodium-free: less than 5 mg per serving


  • Very low sodium: 35 mg or less per serving or, if the serving is 30 grams (g) or less or 2 tablespoons or less, 35 mg or less per 50 g of the food


  • Low-sodium: 140 mg or less per serving or, if the serving is 30 g or less or 2 tablespoons or less, 140 mg or less per 50 g of the food


  • Light in sodium: at least 50% less sodium per serving than average reference amount for same food with no sodium reduction


  • Lightly salted: at least 50% less sodium per serving than reference amount


  • Reduced or less sodium: at least 25% less per serving than reference food

The salt that you add while cooking or eating can easily put you over your limit for the day. Each teaspoon of salt contains about 2,300 mg of sodium. Some techniques for keeping your sodium intake down are:

  • Prepare food yourself when possible


  • Choose fresh or frozen vegetables


  • Limit or avoid processed, cured or pickled foods


  • Try sodium free seasonings for flavor. Some great options are pepper, fresh garlic, garlic power, fresh onion, onion powder, lemon juice and vinegar


  • Replace high sodium sauces with dry mustard, vinegar, or homemade low sodium sauces


  • When eating out, ask for the sauce on the side and add it sparingly

Too much of a good thing: When it comes to vitamins, more is not always better. For this reason, tolerable upper limits (UL) have been set to let people know what level they need to stay below to avoid any harmful health consequences. There is some evidence to suggest that ascorbic acid (vitamin C) taken in high doses can increase stone formation in people who are at risk. In order to avoid this increased risk, you will need to stay below the UL of 2,000 mg/day that has been set for ascorbic acid. An 8-ounce cup of orange juice contains only about 130 mg of vitamin C, so the most likely way to exceed the safety limit would be through supplements. If you do take a vitamin supplement, be sure to read the labels carefully and speak with your physician if you have any questions.

The oxalate & calcium connection: It was once believed that dietary calcium and oxalate needed to be reduced in order to prevent the formation of calcium oxalate stones. Research has now shown that calcium is actually needed when ingesting oxalate-rich foods in order to assist with decreasing the absorption of the oxalates. The other necessary intervention is to limit your overall intake of oxalate-rich foods. These foods include beets, chocolate, coffee, cola, nuts, rhubarb, spinach, black tea, and wheat bran.

Weight it out: One of the numerous health benefits of weight loss could be lowering your risk of kidney stones. In a recent study of over 200,000 people, being obese and gaining the most weight over the 46 year follow-up period put people at the greatest risk for kidney stones. The risk was solely based on weight and not the diet or fluid intake. If you are overweight, cutting your calories and following a well balanced diet may be the key to kidney-stone prevention.

How can your diet decrease the risk for calcium stones?

Calcium connection: It was once believed that dietary calcium was responsible for calcium stones, and the recommendation was to avoid calcium rich dairy products. Numerous studies have now refuted this advice. In fact, foods high in calcium, including dairy products, are believed to help prevent stone formation. One study of over 45,000 men found that those who consumed fewer than 850 mg of calcium per day were at an increased risk for kidney stones. The goal is to meet the guidelines for an adequate intake of calcium through your diet. The Recommended Adequate Intakes set for calcium are:

    0 to 6 months-210 mg
    7 to 12 months-270 mg
    1 to 3 years-500 mg
    4 to 8 years-800 mg
    9 to 13 years-1300 mg
    14 to 18 years-1300 mg
    19 to 50 years-1000 mg
    51+ years-1200 mg

Fluid fix: Drinking enough fluid will reduce the concentration of stone-forming minerals in the urine by diluting it. The goal is to drink at least 10 full glasses of fluid each day (at least half should be water) in order to produce over 2 quarts of urine on a daily basis. The average daily output of urine is about 1½ quarts, so this is somewhat higher. Some ways to reach your fluid goals are:

  • Have one cup before and after each meal
  • Drink with your meals
  • Drink with your snacks
  • Drink during activities: computer, TV watching, and commuting
  • Eat a lot of water-rich foods (for example, soup, fruit, vegetables)
  • Drink as little caffeine and alcohol as possible

Phytate phenomenon: There is some evidence that some fiber-rich foods that contain a compound called phytates can help prevent both kinds of calcium stones. Phytates are found in natural dietary bran, legumes, beans, and whole cereals.

Quick GuideKidney Stones: Symptoms, Causes, and Treatment

Kidney Stones: Symptoms, Causes, and Treatment

Tea time: A couple of studies done on rats have shown a decrease in stone formation with the consumption of green tea. At this time, there is no human data to support these findings. Hopefully, more studies will be done to assess the effectiveness of green tea in the prevention of kidney stones. Until then, enjoy some green tea as part of your daily fluid intake.

What foods increase the risk for uric acid stones?

Uric acid stones are associated with a high purine intake and acidic urine. When there is too much uric acid in the urine, stones can form.

Cut the purines: Purines are found in high concentrations in anchovies, sardines, herring, mackerel, scallops, gravy, meat, and meat products. Organ meats such as liver, brain, sweetbread, and kidney have particularly high levels. Studies have found that a high intake of purines can increase the amount of uric acid in the urine, leading to the formation of uric acid stones. Protein substitutes for these high purine foods are:

  • Dairy products
  • Legumes
  • Soy products
  • Tofu
  • Lentils
  • Whole grains
  • Vegetables

Alcohol alert: The studies linking alcohol to uric acid levels have focused on gout. Gout results from an accumulation of too much uric acid that can lead to deposits of hard lumps of uric acid in and around the joints and cause inflammation. Chronic or untreated gout can lead to kidney stones. Research has found that drinking beer showed the strongest risk of developing gout. While other spirits (for example, brandy, whiskey, vodka, etc.) have also been shown to increase the risk of developing gout, wine was not found to do so. There are some red wines and stouts that contain purines or oxypurines, which can lead to increased purine load, so you will need to be cautious with red wine as well. Even without gout, if you have a history of uric acid stones, it would be beneficial to limit your consumption of alcohol.

What foods decrease the risk for uric acid stones?

Dairy connection: Research has shown that milk and yogurt consumption can lower serum uric acid levels. In one study, those who consumed milk one or more times per day had a lower serum uric acid level than did those who did not drink milk. Similarly, those who consumed yogurt at least once every other day had a lower serum uric acid level than did those who did not consume yogurt. Your goal should be to meet the Recommended Adequate Intakes set for calcium:

    0 to 6 months-210 mg
    7 to 12 months-270 mg
    1 to 3 years-500 mg
    4 to 8 years-800 mg
    9 to 13 years-1300 mg
    14 to 18 years-1300 mg
    19 to 50 years-1000 mg
    51+ years-1200 mg

Fluid fix: Drinking enough fluid will reduce the concentration of stone-forming minerals in the urine by diluting it. The goal is to drink at least 10 full glasses of fluid each day (at least half should be water) in order to produce over 2 quarts of urine on a daily basis. The average daily output of urine is about 1½ quarts, so this is somewhat higher. Some ways to reach your fluid goals are:

  • Have one cup before and after each meal
  • Drink with your meals
  • Drink with your snacks
  • Drink during activities: computer, television watching, and commuting
  • Eat a lot of water-rich foods (for example, soup, fruit, vegetables)
  • Drink as little caffeine and alcohol as possible

If you have any health conditions, speak with your physician before making any drastic changes in your diet. Also keep in mind that you could have stones that appear after you make your changes in your diet. This does not mean that the diet did not work; it means that the stones were there before, so you would need to give your diet more time to see if it works.

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Quick GuideKidney Stones: Symptoms, Causes, and Treatment

Kidney Stones: Symptoms, Causes, and Treatment

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Reviewed on 5/2/2007

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