Know Your Stones...Protect Your Kidneys (cont.)

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.

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


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