The chemistry behind the kidney stone formation is complex. Some experts believe that the ratio of calcium to magnesium, another essential mineral in the diet is important.
Kidney stones develop when urine concentrations of minerals and other dissolved materials get so high that the minerals can no longer remain dissolved. Stones can also form if the pH (acid-alkaline balance) of urine is too high or too low. In all cases, the minerals form insoluble crystals and precipitate, or drop out, of the urine, exactly the same way too much sugar drops to the bottom of a glass of iced tea. The crystals collect in the kidney ducts, slowly solidifying into stones.
Most doctors today rely on both dietary measures and drugs, often diuretics (which decrease urinary calcium and increase urine flow), to kepp kidney stones from coming back.
Different Types of Stones. While some dietary changes seem to help prevent all kinds of kidney stones, a few work for only certain types of stones. So it's important to know the kind of stone you have formed. The only way to do that is with laboratory analysis of a captured stone. The most common type of kidney stone, made of calcium oxalate, is found in more than 80% of cases.
It's also important to know why you're forming stones. The only way to do that is with urine and blood tests and measures of levels of calcium. People form stones for lots of reasons, including metabolic abnormalities and infections.
Some experts recommend that peple who have had one or more bouts of calcium oxalate stones make sure that they get at least the Daily Recommended Value of magnesium, 400 milligrams, through diet and supplements, if necessary.
Most kidney specialists believe that magnesium plays only a minor role in the treatment of kidney disease. But some researchers and some doctors with an interest in nutrition think that magnesium's potential for preventing stones has not been fully appreciated.
Some Helpful Tips Many doctors consider the following dietary adjustments proven and effective kidney stone stoppers:
- Stay well-watered. The more that you take in. the less chance that minerals in your urine will form crystals that lead to stones. Aim for at least half-gallon of water a day or an eight-ounce glass every other working hour. Drinking enough water helps prevent all types of stones, and it's especially important for people who live in hot, dry climates.
- Shake the salt habit. Too much salt raises urine calcium levels, which ups your risk of kidney stones. You'll be on a safer side if you only take 2,400 milligrams a day, about half of the usual intake. To go that low, avoid most processed foods, especially lunchmeats, soups and frozen dinners, and toss out your saltshaker.
- Don't be so sweet. Sweet treats raise urine calcium levels at the same time they decrease urine volume, causing a very high concentration of calcium in the urine. If you must eat dessert, make a small one. And avoid sweet snacks.
- Don't have a cow (or a pig, or a chicken). For people eating the typical American diet, high meat consumption is associated with calcium oxalate stones, studies show. Animal protein increases the concentration of both calcium and uric acid in the urine. Many men with kidney stones are big meat-eaters.
- Don't cut back on calcium. Cutting back on dairy products and other calcium-rich foods used to be standard advice for people with kidney stones. Turns out, though, that people who get more calcium in their diets are less likely to develop kidney stones than people who get less calcium. If you're taking calcium supplements, though, don't go above 1,000 milligrams a day without your doctor's okay.
- Go easy on C. The Daily Recommended Value for vitamin C is a mere 60 milligrams, but many people ingest more to take advantage of vitamin many healing benefits. It's especially important for people who've had kidney stones to not jump on the vitamin C bandwagon with too much enthusiasm. Some doctors recommend that if you are taking vitamin C supplements, you stay below 500 milligrams. That's because one by-product of vitamin C metabolism may be oxalate, which is half of the most common kidney stone.
- Don't worry about coffee—or beer Although both of these beverages up calcium excretions, they also increase urine volume, so there's no increase in calcium concentration in the urine.
- Scratch some oxalates off your grocery list. Researcher initially thought that the greater the oxalate level in a food, the more likely it was to increase the risk of forming a kidney stone. It In fact, only certain oxalate-containing foods are likely to significantly increase urinary oxalate: rhubarb, spinach, beets, nuts, chocolate, wheat bran, strawberries, peanuts, and almonds. However, there's still no universal consensus on which oxalate-containing foods belong on this list. The best approach in the prevention of recurrent kidney stones is simply to avoid all high-oxalate foods:
High-Oxalate
(> 10 milligrams per serving)
| High-Oxalate
(> 10 milligrams per serving)
|
|
Beets
Celery
Collards
Dandelion greeds
Eggplant
Escarole
Green beans
Kale
Leeks
Okra
Parsley
Parsnips
Potatoes
Pumpkin
|
spinach
Squash, yellow summer
Sweet potatoes
Swiss chard
Tomato sauce, canned
Turnip greens
Watercress
Concord grapes
Figs, dried
Kiwi
Lemon peel
Orange peel
Rhubarb |
Vitamin B6 provides anti-oxidant protection. Along with magnesium, some doctors recommend vitamin B6 to people who get kidney stones. A vitamin B6 deficiency throws up a roadblock in the body's metabolism, so more oxalic acid is made, which means that high amounts get into the urine. Oxalic acid then combines with calcium to form insoluble calcium oxalate, the stuff from which stones form.
Medical Alert: No supplement program dissolves kidney stones that have already formed. If you have kidney or heart problem, check with your doctor before taking supplement magnesium. Some doctors recommend taking no more than 50 milligrams of vitamin B6 without medical supervision. Large doses have been associated with nerve damage.
Cranberries and kidney stones. In some studies cranberries have been shown to decrease the amount of ionized calcium by over 50% in patients with recurrent kidney stones. Quinic acid, a component of cranberries, is not metabolized by the body and is thereby excreted unchanged in the urine. This increases the acidity of the urine, which then prevents calcium and phosphate ions from forming insoluble stones [17].