Every so often I get a call from a patient asking about kidney stones. That’s always a good opportunity for me to read up on the latest research. There is a lot of misinformation on the Internet regarding the relationship between the consumption of certain foods and risk of developing kidney stones. You all know how much I love evidence-based information, so I am relying on good ol’ science to help, again.
By the time patients get to me, they already know the excruciating pain that accompanies passing something as small as a grain of sand--a kidney stone-- but do they know that genetics, environment (including diet), physiology, and medications can all influence their development?
First, let’s look at the different kinds of kidney stones:
Calcium stones make up 80% of kidney stones. While most are in the calcium oxalate form, they can also be of a calcium phosphate nature. Oxalate occurs naturally in food, as well as manufactured by the liver. Phosphate stones result from metabolic conditions, such as renal tubular acidosis where the kidneys can’t acidify the urine.
Struvite stones (10%) form in response to an infection, such as a urinary tract infection. They are made of magnesium, ammonium and phosphate.
Uric acid stones (5-10%) can form when the urine is too acidic. Certain genetic factors also may increase your risk of uric acid stones, as well as sub-optimal hydration or a high-protein diet. Uric acid is related to gout.
Cystine stones (<1%) are rare and occur when cystine leaks from the kidneys into the urine. This is strictly a genetic disorder.
What are some diet and lifestyle changes to make?
Well, that’s where the controversy exists. There are lots of oxalate food lists floating around the Internet but the American Urological Association does not suggest overly restrictive low-oxalate diets. That being said, there are high oxalate foods— spinach, almonds, rhubarb, beet greens, nuts, chocolate, tea, bran, peanuts, and strawberries— that should definitely be moderated by those people prone to stone formation.
Here are some tips to help stones from recurring:
1. HYDRATION: High risk stone formation is attributed to low urine volume that can result from dehydration from an illness or excess heat, or from not drinking enough fluids. The more concentrated your urine is (i.e dark yellow) means that there is less fluid to dissolve stones in. The goal is to drink 3-4 quarts of water a day. Lemon juice helps to increase the acidity of the liquid, which has an alkalizing effect in your body (gotta love science!). I recommend adding 4 ounces of lemon juice to two quarts of water. Note, grapefruit juice is not a recommended fluid choice. And, any fluids with high fructose corn syrup (soda, punch) can lead to uric acid stones, which can lead to gout.
2. SODIUM. Table salt contains sodium and chloride. Too much salt in the diet is a risk factor for calcium stones. Too much sodium in the body promotes a condition called metabolic acidosis, which releases calcium from the bone into the blood, which leads to excess calcium being excreted in urine. Reducing salt in the diet lowers urine calcium, making it less likely to form stones. Sodium can also cause high calcium levels in the urine. Sodium goal is less than 2300 milligrams a day.
3. CALCIUM: Lowering the amount of calcium in your diet rarely stops stones from forming. In fact, naturally-occurring calcium found in food helps to bind oxalates in the gut so it isn’t absorbed by the body (and hence, it’s not excreted in the urine. The resulting decrease in urinary oxalate actually reduces the risk of stone formation.
Strive for 1000-1200 milligrams (mg) of calcium a day in your diet. An 8-ounce glass of milk contains approximately 300 mg. The new food labels now tell you actual milligrams, making it easier to figure out. Calcium supplements are not recommended, as they increase the risk of developing stones.
4. PROTEIN: Animal proteins like meat, dairy, poultry, or fish increase urinary calcium by reducing urinary pH levels. Diets high in animal protein can raise acid levels in the body and in urine. This puts people at an increased risk to produce uric acid and/or calcium oxalate stones. Don’t exceed more than 0.75 oz of protein per pound body weight. (i.e. if you weigh 200 pounds, that’s 150 grams of protein)
5. DASH Diet: This diet is jam packed with fruits and vegetables which contain anti-oxidant properties, and nutrients such potassium, fiber, magnesium, and calcium that may play a role in helping to keep stones from forming. Studies have shown that potassium reduces urinary calcium excretion, and people who eat high amounts of dietary potassium appear to be at low risk of forming kidney stones.
In summary, remember, there is no "one-size-fits-all" diet for preventing kidney stones. Everyone is different, so it’s best to work with your health care practitioner to evaluate your own individual circumstances.
Sophie
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