1 in 10 people in the U.S. experience kidney stones in their lifetime, and around 500,000 people go to the emergency room every year due to kidney stones. Your kidneys have several functions for overall health, including controlling blood pressure, maintaining fluid balance, and removing waste. When the urine is too concentrated with minerals and salts, these minerals deposit and crystallize, forming stones that can impact any part of the urinary tract. This can cause blockages leading to painful sensations while in the body as well as when they are passed through the urine. There are variations of kidney stones, and not all are formed the same way.
Types of Stones: Calcium Oxalate: The most common. They occur when calcium and oxalate bind within the urine. Inadequate calcium and fluid intake are often contributors. Dietary management is possible. Uric Acid: Caused by inadequate hydration and fluids, in the presence of a high protein diet consisting of high purine foods. Levels can be lowered through dietary management. Struvite: Caused by infections in the upper urinary tract. Cystine: Rare and said to occur with family history.
What are the Risk Factors?
Family History: If someone in your family has had kidney stones, you are more likely to develop them.
Comorbidities: Overweight/obesity, GI diseases, and other medical conditions increase the risk of developing kidney stones.
Dietary Factors: Diets high in salt, protein, and added sugar may increase risk of stone formation, as well as inadequate fluid intake.
Kidney stones can be managed and prevented through nutrition management of dietary factors. Recommendations for dietary factors can aid in decreasing the workload of the kidneys and aid in the passing of stones.
Changes in oxalate concentration in the urine have greater effect than calcium, because much less oxalate is present in the urine. Foods high in oxalate include: • potatoes • legumes • nuts • wheat bran • spinach • chard • rhubarb • beets • raspberries • pumpkin • eggplant • chocolate • tea Because high oxalate foods are also healthful, limiting amounts versus restricting them is recommended.
Research also states that eating oxalate foods with calcium-rich foods at meals increases the likelihood that they bind together in the stomach prior to reaching the kidneys, preventing stone formation. When limiting oxalates, recommendations include 60mg per day. This is equivalent to about 1 cup of raspberries, cashews, or raisin bran.
Calcium Despite popular belief, calcium should not be restricted in kidney stone prevention or management. Calcium is a key part of a healthy diet, and low levels are also said to increase oxalate in the urine, increasing the risk of stone formation. The normal daily allowance (RDA) for calcium is recommended: Calcium intake should be divided between three different meals for maximum absorption. • 1,000 mg per day for men. This is the equivalent of two 8 ounce glasses of milk. • 1,200 mg per day for women.
Fluids The National Kidney Foundation recommends 12 cups of water per day for all four types of stones to both manage and lessen your risk of new stone formation. Adequate hydration will keep your urine less concentrated, making it more difficult for stones to form.
Purines Purines are associated with uric acid stones. High purine foods and beverages include the following: •beer & alcohol •carbonated drinks •red meats •shellfish •animal organ meats
Limiting these foods reduces the level of uric acid in the blood and the risk of stone formation in the urinary tract. The recommendations include: • Limit meat to 3 ounces per meal. • Incorporate plant-based protein sources at least twice a week such as beans, nuts, edamame, or tofu.
Sodium Excess sodium must also be excreted in the urine, making the urine more concentrated. Recommendations for sodium are: • 2,300 mg/day for the average adult and children ages 14 and older. This is equivalent to 1 tsp of table salt per day. • 1,500 mg/day for adults with hypertension or other cardiac issues
Added Sugars Excess added sugars within the diet are also excreted through the urine, contributing to higher concentration of minerals in the urine. Fructose is said to also increase production of uric acid in the urine, and possibly increases oxalate and calcium presence in the urine.
For these reasons, an emphasis is placed on adequate intake of vegetables with limits on added sugars to the recommendations of under 25g per day for women and 38g per day for men (based on 5% total calories of a 2,000 calorie per day d