Kidney stones are caused by an accumulation of mineral salts, combined mostly with calcium, which may lodge anywhere along the course of the urinary tract. They are usually comprised of calcium oxalate, calcium phosphate or, less commonly, uric acid crystals.
Most stones form in the kidney or upper urinary tract. It is calculated that 10% of men and 5% of women suffer from them. Their incidence seems to be increasing.
Kidney stones are often symptomless and frequently pass out of the body naturally via the urine. However, if a large stone blocks the urinary tract, it can cause problems such as pain and discomfort, and procedures such as surgery or ultrasound may be necessary to remove it.
Symptoms of kidney stones can include pain radiating from the upper back to the lower abdomen, frequent urination accompanied by pus and blood, and occasionally chills and fever. If the stones migrate down the ureter to the bladder they can cause extreme abdominal pain sometimes accompanied by fever.
Calcium, uric acid and phosphates would usually remain in solution in the urine provided the urine remains at the correct pH. If the urine becomes too alkaline these substances will tend to precipitate out and form a stone. We usually secrete protective factors to prevent the crystallisation of these substances in our urine. If these protective factors are overwhelmed, crystallisation can occur.
Kidney stones can also be associated with disorders causing increased calcium excretion in the urine, such as hyper-parathyroidism, absorptive hypercalcuria, and hyperthyroiditis.
Oestrogen deficiency after the menopause can lead to increased calcium being reabsorbed from the bones and its eventual deposition in the urine, increasing the likelihood of kidney stones.
Low levels of glutamic acid, often due to a B6 deficiency, usually occur with recurrent kidney stones. An increased concentration of glutamic acid in the urine decreases the calcium oxalate precipitation.
Risk factors associated with kidney stones
Factors favouring stone formation can include a decreased urine volume; an increased excretion of stone constituents, along with pH changes in the urine and low levels of substances which solubilise stone constituents.
Risk factors include:
• High intake of sugar and refined carbohydrates
• High alcohol intake
• High coffee consumption
• High intake of animal protein
• High salt intake
• High intake of saturated fats
• High intake of phosphoric acid (from fizzy drinks)
• Low intake of fibre
• Deficiency in Vitamin B6
• Excess weight
Dietary and lifestyle suggestions for the prevention of kidney stones
Since most kidney stones are high in calcium and oxalic acid, the major dietary and nutritional measures to counteract kidney stone formation are aimed at affecting the metabolism of these two substances.
• Avoid high protein intakes, especially of animal protein, which otherwise would lead to calcium losses in the urine and possibly its accumulation in the kidneys. A high intake of protein will also increase the amount of uric and oxalic acids in the urine, since they are both by-products of protein breakdown by the liver.
• Avoid dairy products, which can precipitate kidney stones by increasing the urinary concentration of calcium. Calcium can be obtained from green leafy vegetables, tofu and seeds instead.
• Excess weight or insulin insensitivity can lead to increased calcium being excreted in the urine. After ingestion of sugar or refined carbohydrates the pancreas will release insulin, which causes a rise in urinary calcium. Therefore it makes good sense to avoid too much sugar in the diet, and instead opt for foods with a low glycaemic value which will release sugar slowly into the bloodstream.
• Decrease your intake of phosphoric acid-containing soft drinks which can contribute to disordered calcium metabolism. Fizzy drinks can increase calcium loss in the urine.
• Avoid eating too much oxalic acid-containing food such as asparagus, beets, parsley, rhubarb, sorrel, spinach, Swiss chard and other vegetables of the cabbage family, cocoa and instant coffee. Reduction in dietary oxalate may decrease the oxalate secreted in the urine, and thus lower the rate of stone formation.
• Drink plenty of fluid, at least 2 – 2.5 litres of water spread throughout the day, to help dilute the urine. Avoid tea, which contains a high concentration of oxalic acid.
• Drinking two pints of cranberry juice has been found to decrease urinary ionised calcium levels by 50%. Cranberry juice will also help to acidify the urine, which will discourage stone formation.
• Reduce your salt intake. Too much salt can lead to a loss of calcium from the urine. Season foods with herbs and spices, or use Solo salt instead, and avoid processed foods which can be high in salt.
• Cut down your alcohol intake. Stone formers have been found to have approximately double, on average, the amount of alcohol consumption than those of non-stone formers, because alcohol increases the excretion of uric acid, calcium and phosphates.
• Cut down on coffee. Caffeine has been found to increase the amount of stones in the urine. Choose instead herbals teas, dandelion coffee or grain-based coffee substitutes such as Yannoh and Barley cup.
• The urinary glycoprotein which inhibits calcium oxalate crystallisation requires Vitamin K for synthesis. Vitamin K is contained in chlorophyll, so eat plenty of green leafy vegetables. Generally, increase the amount of whole, unprocessed foods in the diet such as whole grains, legumes, vegetables, fruits, nuts and seeds. A high fibre diet will guard against the formation of kidney stones.
• Aluminium can increase the excretion of insoluble calcium, so avoid cooking with aluminium pots wherever possible.
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Elizabeth Hartland has a Bachelor of Science Degree in nutrition, together with a Diploma from the Institute of Nutritional Therapy. She is married with two young children and has a passion for good nutrition and helping others to find better health. 282 427 652
