A study from Princeton University states that about 10% of people will suffer from kidney stones of some sort in their lifetime. 80% of these people will have calcium based stones, and 80% of those people will have calcium oxalate stones. It stands to reason that this is the primary type of stone we should try to avoid with some simple and healthy modifications to our diet.
There are five different types of kidney stones: calcium oxalate, calcium phosphate, magnesium ammonium phosphate (struvite), uric acid, and cystine stones. Some of these are more common in people with a genetic predisposition, or with abnormal kidneys, but as I stated earlier, 80% of stones are calcium based. Many research studies have been done on patient’s who have a history of kidney stones, and a few long term studies have been done on people with no prior history of stones. Here are the conclusions.
The cornerstone of prevention is to increase fluid intake. The benefit appears to be linear with fluid consumption up to 2.5 liters a day. A good goal would be 2.5–3 Liters of fluids per day. This helps flush the kidneys of calcium that may want to dissolve out in the kidneys. Similar to a swift moving river depositing no silt, busy kidneys will get less stones. Studies show that drinking coffee and beer decreases the risk of stones. While drinking grapefruit juice consistently increases stone risk for unclear reasons, whereas lemon juice, might have beneficial effects.
Reducing dietary sodium intake to less than 2 grams a day has been shown to decrease the incidence of stones as well. Salt causes our body to retain fluids, and therefore, the kidneys are not flushing out as well as they should be.
A diet with only moderate amounts of protein will help as well. The recent popularity of diets low in carbohydrates and high in animal proteins has refocused attention on protein intake as a risk factor for stones. Patients with recurrent stones should limit their protein intake to less than 80 grams per day. This may be why many vegetarians never get kidney stones
Vitamin C supplements are questionable. One study from Princeton says “the use of vitamin C supplements may increase the levels of oxalate and be associated with an increased risk of stone formation; therefore, the dose of these supplements should be limited to less than 1000 milligrams per day.” While the authors of The Vitamin C Connection state that, “Vitamin C in the urine tends to bind calcium and decrease its free form. This means less chance of calcium’s separating out as calcium oxalate (stones).”
Reducing phosphorus intake has also shown to be effective. High levels of phosphates in the blood will cause our bones to give up their calcium. This puts more calcium in the blood, and may be causing our kidneys to deal with this by filtering it our as stones. The biggest source of phosphoric acid in the American diet is carbonated beverages – especially dark colored colas.
Some smaller studies have also shown benefits with taking fish oils, supplementing with 300-500mg of magnesium, taking a daily B-complex vitamin, and one study suggested becoming vegetarian for people with chronic kidney stones. With all of this said, it is important to note that kidney stones are often caused by what we eat, and how often we eat it. Although genetics may play a role in our predisposition, these healthy changes may help us beat out those genes our parents gave us.