Introduction Kidney stones are one of the most common disorders of the urinary tract. Kidney stones affect about 12% of men and 5% of women by the time they are 70 years old. Men are about twice as likely to form kidney stones as women. Most people who experience one episode of kidney stones will experience another and many go on to have multiple recurrences. Aside from the extreme pain involved in passing a kidney stone there is also the danger of permanent damage to the kidney.
Why Dietary Control is Important Those who have formed one calcium oxalate stone have a 50% chance of forming additional stones within 10 years (Menon & Resnick, 2002). With appropriate education, patients can exercise some control over stone disease and reduce their chances of forming stones through dietary modifications and medication.
Metabolic Causes of Kidney Stones Hypercalciuria - Calcium is absorbed from food in excess and is lost into the urine. This high level of calcium in the urine causes crystals of calcium oxalate or calcium phosphate to form in the kidneys or elsewhere in the urinary tract. Hyperuricosuria - Uric acid metabolism (gout). Meat, fish, chicken are restricted due to breakdown products that produce uric acid crystals. Hyperoxaluria - the body produces too much oxalate, a salt. When the urine contains more oxalate than can be dissolved, the crystals settle out and form stones. Cystinuria - too much of the amino acid cystine, which does not dissolve in urine, is voided, leading to the formation of stones made of cystine. Renal tubular Acidosis a condition in which the kidneys are unable to excrete normal amounts of acid.
Dietary Causes of Renal Stones High Low Dehydration Water intake Foods rich in Oxalate Calcium than RecommendedAnimal protein – Meat, Egg, Low Magnesium Chicken Salt – Sodium Potassium than Recommended Phosphate – Aerated Citrate or Citric Acid (Vit C) carbonated drinks Obesity – Weight Gain Dietary Fiber
Water A simple and most important lifestyle change to prevent stones is to drink more liquids - water is best. Someone who tends to form stones should try to drink enough liquids throughout the day to produce at least 2 litres of urine in every 24-hour period. It is not the quantity of fluid consumed that is important, but rather the fluid voided that should be measured. Patients living in hot or dry conditions, or who exercise and perspire significantly, will need to drink even more liquid to maintain adequate urine output.
Dehydration Kidney stones tend to develop more frequently in the summer months, Because we sweat more when we are hot, we need even more water to replace what we are losing. One can tell if one is well hydrated if the colour of the urine is clear to very light yellow. If your urine is bright yellow, you need to drink more fluids. water reduces the concentration of the minerals that might crystallize into stones.
Oxalate combines with calcium - insoluble Calcium Oxalate crystals Less than 50 mg of oxalate per day in the diet. Foods high in Oxalate Content Almonds Peanuts Amla Phalsa Amaranth, tender Rhubarb Beets Soy products (tofu) Blackberries Spinach Chocolate/cocoa /chocolate drink mixes Strawberries Cashew nuts Swiss chard Okra Tea Gooseberries Wheat bran Grapefruit Raspberries (black)
Food Portion Oxalate (mg) Calcium (mg)* Beet greens, cooked 1/2 cup 916 82Rhubarb, stewed, no sugar 1/2 cup 860 52 Spinach, cooked 1/2 cup 750 122 Beets, cooked 1/2 cup 675 16 Swiss Chard, cooked 1/2 cup 660 50 Spinach, frozen 1/2 cup 600 122 Cocoa, dry 1/3 cup 254 36 Okra, cooked 1/2 cup 146 50 Sweet potatoes, cooked 1/2 cup 141 14 Peanuts 1/3 cup 113 23 Tea 1 cup 75 0 Pecans, halves 1/3 cup 74 11 Wheat germ 1/4 cup 67 12
Myth - Dietary Calcium & Kidney Stones A recent study conducted Brigham and Women’s Hospital and Harvard Medical School on more than 90,000 women, showed "that women with the highest intake of dietary calcium had the lowest risk of kidney stones." Calcium is believed to neutralize the absorption of oxalate, has been linked to kidney stone formation." For those taking calcium supplement the risk of kidney stones increased slightly. “Calcium supplements are often not taken in conjunction with meals, limiting the calcium’s ability to neutralize the absorption of oxalate." This is why diet to increase calcium intake, and avoid supplements.
Dietary Protein and Kidney Stones A small amount of dietary protein can be converted to oxalic acid in the body and excreted as such in the urine. In addition, dietary protein is known to enhance calcium excretion in the urine. When the average dietary protein was reduced from 86.5 to 54 g/day there was a reduction in urinary calcium excretion of nearly 50% (from 9.35 to 6.45 mmol/day). Most protein-rich foods may also increase urinary uric acid levels. This is because most high-protein foods (except milk) usually contain a large amount of purines that breakdown into uric acid. The risk of kidney stone formation seems greater from animal than vegetable proteins,
Animal Protein• The higher sulfur amino acid content of animal compared to vegetable proteins may increase calcium excretion. In addition, excess sulfur-containing amino acids will increase a rare form of kidney stones (containing cystine) in people with an inherited metabolic defect.
Magnesium Take a magnesium supplement of at least the US RDA of 300-350 mg/day (more may be desirable in order to maintain an ideal 1:2 balance of magnesium to calcium) A vitamin B6 and magnesium deficiency may also cause stone formation. A Swedish research group found that taking both daily stopped stone formation in 90% of their patients. Magnesium, like calcium, can bond with the oxalate and acts as a inhibitor of the formation of calcium oxalate crystals in the urine. The mean stone episode rate decreased from 0.8 to 0.08 stones/year on Magnesium supplement and 85% of the patients remained free of recurrence during follow-up, whereas 59% of the patients in the control group continued their stone formation. (Johansson and Backman U)
Sodium Diets low in sodium are effective in reducing stone formation by decreasing the excretion of calcium. Because calcium and sodium compete for reabsorption in the renal tubules, excess sodium intake and consequent excretion result in loss of calcium in the urine. High-sodium diets are associated with greater calcium excretion in the urine (Lemann, 2002). Aim for < 3000 milligrams of sodium per day.
To reduce the sodium in your diet: Enjoy your food without added salt. Use vinegar, herbs, & spices to flavor your foods instead of salt. Cook without salt. Check food labels. If the food contains more than 250 milligrams of sodium per serving, it contains too much sodium. In general, the more processed a food is, the greater is its sodium content
Potassium and kidney stones• In one study of over 45,000 men, those whose daily intake of potassium was more than 4.3 grams per day were 50% less likely to develop kidney stones than those with potassium intakes of less than 3 grams per day.• Potassium rich foods as fruits and vegetables.
Soft or Carbonated Drinks• Not only dehydrates making one more prone to kidney stones, but also contains phosphates, which is linked to higher kidney stone recurrence.• Dark soft drinks tend to contain oxalates, which further increase ones susceptibility to kidney stones.• Any caffeinated beverage is dehydrating, so for every cup of a caffeinated beverage you drink, do drink another glass of filtered water.• Sugary drinks tend to mess with calcium and magnesium absorption, once again increasing ones risk for kidney stones.
Your body must buffer the acidity of soft drinks with calcium from your own bones. As this calcium is eliminated through your urine, it slowly forms kidney stones. Carbonated beverage consumption has been linked with diabetes, hypertension, and kidney stones, all risk factors for chronic kidney disease. With kids drinking so much in the way of sugary drinks and soda pop now, children as young as 5 are being afflicted with kidney stones.
Citrate• The citrate acts as an inhibitor to stone formation. Lemonade made with frozen concentrate, real lemon juice or real lemons is one of the fluids recommended for its citrate content.• Orange and carrot juices are high in citrates which inhibit both a build up of uric acid and also stop calcium salts from forming. (Carper, J. "Orange Juice May Prevent Kidney Stones," Lancaster Intelligencer-Journal, Jan 5, 1994)
Weight Curhan and colleagues (1998) found that "the prevalence of stone disease history and the incidence of stone disease were directly associated with weight and body mass index. However, the magnitude of the associations was consistently greater among women". Obesity increases the risk of kidney stones, but its theorized that insulin resistance, a common condition in obese people, increases the amount of calcium in the urine. This, in turn, contributes to the formation of crystals that develop into kidney stones.
• Men > 220 pounds had a 44% increased risk of developing kidney stones compared with < 150 pounds. Older women in the same high-weight category had an 89% increased risk for kidney stones, while heavy younger women had a 92 % increased risk. (Taylor).• Men in the highest category of BMI had a 33% increased risk as in the lowest category. Older women in the highest category had a 90 % increased rate and younger women more than double the risk.• Women with the largest waist circumferences had a 71% greater risk of kidney stones compared with the lowest waist circumferences. Men had a 48% greater risk.• Men who had gained > 35 pounds since they were 21 had a 39% higher risk of getting stones compared with men whose weight remained stable. Similarly, older women who had gained the same amount of weight since they were 18 had a 70% increased risk while younger women had an 82% increased risk.
Dietary Fiber Fiber is the indigestible part of plants. There are two types of fiber: soluble (dissolves in water) and insoluble. Both provide important functions in the body. Insoluble fiber (found in wheat, rye, barley, and rice) help to reduce calcium in the urine. It combines with calcium in the intestines, so the calcium is excreted with the stool instead of through the kidneys. Insoluble fiber also speeds up movement of substances through the intestine, so there will be less time for calcium to be absorbed.
Sugar Kidney stones are associated with high sugar intake, so eat less (or no) added sugar (J. A. Thom, et al "The Influence of Refined Carbohydrate on Urinary Calcium Excretion," British Journal of Urology, 50:7, 459-464, December, 1978) There is evidence that one third of the population shows increased risk factors for kidney stone disease after consuming sugar. These effects of sugar consumption are thought to be due to the increased secretion of insulin, which results in increased calcium excretion by the kidneys. (Blacklock NJ et al)
Alcohol People should have no more than two drinks-two 12-ounce servings of beer or two 5-ounce servings of wine or two 1.5- ounce servings of hard liquor-a day. Alcohol per se does not lead to kidney stone formation. It does make stone sufferers pass more urine that can lead to a dehydrated state. Alcohol likewise indirectly inhibits the kidneys’ ability to excrete uric acid from the human body. Cases of men who regularly drink alcoholic beverages (about two to four bottles a day) like beer upped their risks of suffering from gout, which can lead to stone formation.
Vitamin B B-6 deficiency produces kidney stones in experimental animals. B6 (10 mg a day) lowers the amount of oxalate in the urine. In high doses, it is also used medically to treat kidney stones. B-6 deficiency is very common in humans. B-1 (thiamine) deficiency also is associated with stones (Hagler and Herman, "Oxalate Metabolism, II" American Journal of Clinical Nutrition, 26:8, 882-889, August, 1973)
Dietary vs Drug Therapy In addition to dietary counseling physicians may utilize various pharmacological agents such as thiazide diuretics, phosphates, allopurinol and potassium citrate to treat patients with recurrent calcium oxalate kidney stones. Urinary citrate drops with increasing urinary acid content so a diet high in whole grains, fruits and vegetables may be more effective than potassium citrate supplementation alone because such a diet will reduce urine acidity and increase potassium, magnesium, and citric acid intake.[Pak CY] However, none of these agents have been proven as effective as a high fiber diet low in salt, animal protein and oxalate rich foods. [Goldfarb S]
Also a diet lower in animal protein, salt and higher in fiber has other health benefits so it seems reasonable for physicians to emphasize dietary therapy for the treatment and prevention of kidney stones. All medications can have adverse side effects. The benefits of reduced stone formation from prescription drug therapy is unlikely to prove greater than the long-term adverse effects associated with the use of the pharmaceutical agents. However, physicians may want to consider the use of supplemental potassium-magnesium citrate as an adjunct to dietary therapy particularly in patients who do not comply with the low salt and meat diet.