Unfortunately, once you’ve had a kidney stone, the chances are high that you’ll have another. Luckily, turning on the kitchen tap and filling up with nature’s most bountiful beverage may be the simple ticket to stone prevention. Certain foods can also help by correcting the balance of salts and minerals in urine and by breaking up crystals before they wreak havoc.
A Diet for Kidney Stones
On any given day, the kidneys filter about 190 litres (200 quarts) of blood to remove salts, water, and waste products that form when the body processes food and liquids. All of this refuse passes as urine through tubes called ureters into the bladder. From the bladder, it flows through a slightly wider tube, the urethra, to exit the body when you urinate. When salts and waste overwhelm the liquid needed to flush them through the system, the waste materials clump together to form stones that can range from the size of a sugar crystal to the size of an apricot.
The more fluid you drink, the more quickly waste passes through your urinary tract, and the less likely you are to get kidney stones.
Aim for: At least 12 cups (3 litres) of fluid spaced throughout the day. If the weather is hot or you’re exercising and sweating, you should drink even more.
A natural acid in lemons called citrate helps to break down waste in the kidneys and prevent stones from forming. In one study, when people drank 125 millilitres (4 ounces) of lemon juice combined with water, the amount of citrate released in the urine doubled.
Aim for: Squeeze fresh lemon juice into the water you drink over the course of the day. Aim for a total of about 1/2 cup (125 milli-litres) of juice.
Low-fat milk, cheese, and other calcium-rich foods
For years, researchers thought that calcium in the diet contributed to the most common type of kidney stones, those made of calcium oxalate. People prone to these stones were consequently told to cut back on milk, cheese, and other dairy products. But the Nurses Health Study, which has been analyzing the diets of thousands of women for decades, has found that the more calcium-rich foods a woman eats, the lower her risk of developing kidney stones. As a result, physicians now advise patients to eat plenty of dairy foods.
It appears that when calcium binds with salts called oxalates in the gastrointestinal tract, the oxalates never enter the bloodstream to reach the kidneys. People prone to kidney stones who take calcium supplements to improve bone strength should be careful to take them with food so the calcium can bind with the oxalates, effectively ushering them away from the kidneys.
Aim for: 1,000 milligrams of dietary calcium per day (1,200 milligrams for people over 50). Get it by drinking 3 cups (750 millilitres) of milk or having a combination of cheese, yogurt, milk, and other calcium sources like sardines.
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Spinach, rhubarb, chocolate, and other foods high in oxalates. This odd trio, along with a number of other foods, contains oxalates, components of calcium oxalate kidney stones. If you have this type of stones, your physician may advise you to limit foods high in oxalates. These include the foods above as well as almonds, beets, figs, Swiss chard, and wheat bran.
Caffeinated coffee, black tea, and cola. Caffeine can cause problems for people prone to stones. It appears to increase the amount of calcium released in urine, increasing the likelihood that calcium will bind with oxalates to form kidney stones. Limit beverages with caffeine to two or fewer cups per day. Because black tea also contains oxalates, you may want to eliminate it altogether.
Salt. People who eat a lot of salt tend to excrete more calcium in their urine than they would on a low-salt diet. Again, the more calcium that passes through the kidneys, the higher the likelihood that it will bind with oxalates to form kidney stones.
Try to limit your salt intake to 2,300 milligrams a day, about a teaspoon (5 millilitres). The best way to cut back is to watch the canned, packaged, and processed foods you eat. Some brands of canned soup, for example, pack more than 1,000 milligrams of sodium into 1 cup (250 millilitres). Even condiments such as ketchup and salad dressing can be loaded with sodium. Check labels and limit sodium to less than 500 milligrams per serving for savory foods and 200 milligrams per serving for sweet foods. Cut back on using the saltshaker, too.
Meat, fish, and poultry. Some people with kidney stones have excessive acid in their urine (called uric acid) that can contribute to kidney stones. Don’t confuse this with other types of acid, like citrate, that can benefit you by preventing the formation of stones in urine. If you are prone to this type of stones, your physician may suggest that you limit meat, fish, and poultry because these foods are high in purines, substances that can break down into uric acid in the body.