Eating to avoid kidney stones

by JANE CLARKE, You magazine, Mail on Sunday,
October 20, 2002

The pain that they cause can be so excruciating that the diagnosis of kidney stones is rarely difficult.

And if you're unlucky enough to have been their victim, understanding how kidney stones originate may help you to avoid facing this agonising scenario all over again.

The reason why I'm tackling the subject this week is because the risk of developing kidney stones (which affect up to 20 per cent of the population in industrialised countries, particularly men) rises during the autumn and winter months, when we start craving richer foods and drinking less water.

Now for the science. Although the kidneys usually dispose of the metabolism's waste products, including excess ions (minute particles of broken-down substances), the urine that they produce only partially dissolves certain combinations of ions, and the remainder may then start clumping together in a narrow section of the urinary tract to form a central core around which a stone may grow.

Kidney stones are usually made up of a salt called calcium oxalate, which means that the more calcium and oxalate ions your urine contains, the higher the likelihood that a stone will form.

You may think that the answer is to reduce your intake of calcium-rich foods, but there are other, far more healthy and effective, nutritional strategies that you should try first, not least because restricting your consumption of calcium-providing foods, such as dairy products, green, leafy vegetable and soft-boned fish, can lead to brittle bones and retard your body's growth and development.

If that wasn't worrying enough, lowering your intake of calcium from the recommended 1,000 to 400 milligrams a day will encourage your body to produce calcitriol, which ultimately increases the amount of calcium that your body retains, with the result that more calcium is deposited in your urine - the last thing you want.

Because insufficient levels of fluid in the body encourage the formation of kidney stones, the first alternative strategy is to boost your intake of water and non-caffeine-containing fluids.

As well as combating the twin threat of your kidneys producing less urine and the concentration of stone-forming ions increasing by drinking 2.5 litres of water or herbal infusions throughout the day, don't drink too much alcohol, which dehydrates the body, and try to avoid caffeine-containing drinks because caffeine significantly increases the level of calcium in the urine.

The second strategy is to decrease your consumption of foods that contain oxalates, notably beetroot, chocolate, rhubarb, spinach, carob and nuts, especially peanuts.

Although the oxalate ions in urine are mainly derived from metabolic processes that have no direct links with dietary oxalates, reducing your intake of these foods can still diminish the number of oxalate ions in your urine.

I'd also recommend eating lots of fibre-packed foods, which help to reduce the amount of calcium that is excreted through the urine, and keeping your intake of purine-rich foods, such as fish roe, anchovies and offal, to a minimum to maintain low uric-acid levels (which, when they are high, can suppress the beneficial action of stone-busting agents) within your urine.

One of the metabolic processes that raises the number of oxalate ions in the urine is the breakdown of animal proteins like meat, fish, chicken and eggs, and animal proteins are also responsible for making the urine more acidic, thus increasing the danger of any calcium oxalate crystallising.

I don't advocate cutting animal protein out of your diet altogether, however, because this would seriously compromise your health, just not eating too much.

As a guideline, base your main meal around some animal protein, such as a large, chicken-breast-sized portion of poultry, lean meat or fish or two or three eggs, then have half this amount for your lighter meal and team both with plenty of wholegrains, vegetables, pasta, rice or potatoes.

I also hope that you'll be inspired to try my peas with pancetta. A light dish that incorporates a little animal protein, it is particularly delicious when served with pasta.


RECIPE: Peas and pancetta

Serves 3-4

2 tblsp olive oil

2 cloves garlic, peeled

30g pancetta chopped into very small pieces-or bacon

a spring onion finely chopped

2lb fresh young peas(unshelled weight) or 400g frozen petit pois, thawed

3 tblsp fresh flat leaved parsley, chopped finely

Squeeze of fresh lemon juice

Sea salt and freshly ground black pepper.

This is one of the easiest, but tastiest vegetable dishes to make. In a deep sauce pan with a lid, saute the garlic cloves in the olive oil until they have turned deep golden brown.

Remove the garlic from the oil, as we only want a hint of garlic and add the pancetta and spring onion. Saute for about a minute until they turn slightly golden brown. Add the peas and cover with the plan lid and turn down to simmering heat.

Cook for about 5 minutes if using frozen peas or 10 minutes for fresh peas. To finish add the lemon juice, parsley and season with salt and pepper.

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