Kidney stones (renal lithiasis) are surprisingly common: Most of us know someone who’s had one. But if it’s in the family, watch out. While there’s no final word on the genetics of it, it is now known that some people are more prone to stones. Men seem to be more prone than women, but children and the elderly are also susceptible. Once you get one, you’re likely to get more.
Kidney stones have recently been shown (in the April edition of Journal of the American Society of Nephrology) to increase one’s chances of getting chronic kidney disease (CKD), so it pays to be careful. Affluence and sedentary lifestyles are common in “stone formers”. High blood pressure and being overweight both increase risk.
Not all kidney stones are equal. Most are precipitated calcium oxalate or phosphate; others include cystine or uric acid; some result from urinary tract infection (UTI).
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Drink more fluid, but know what to avoid
The most obvious solution is a commonsensical one: Drink more water. The target of drinking enough to produce at least 2 litres of urine daily (3.5 litres for cystine stones) coincides with realities such as exercise, hot weather and travel plans. A more achievable aim is colourless urine. However, some juices raise oxalate or phosphate levels, aiding the formation of stones. Citrates hinder stone formation, so lemon juice is excellent; but its close cousins, orange and grapefruit, are oxalate-rich, as is apple. Cranberry also warrants caution: It’s good if the stones have to do with UTI, it’s bad news otherwise.
Coffee, tea, cola or kidney?
Cola is a culprit, being high in phosphates (and sweet), which work against citrates. Coffee and tea can actually help, a 1996 Harvard School of Public Health study found, especially if taken milky. Some studies found alcohol, especially wine, to be helpful in moderation but avoid it if you have uric acid problems.
Oxalate or not?
It used to be the norm to advise patients against oxalate-rich foods—spinach and its relations, chocolate, coffee, cola, nuts (both peanuts and tree nuts), soy, berries (including amla), spring onions, some herbs, poppy seeds, and whole grains (wheatgerm, brown rice). However, dietary oxalates account for only 10-15% of urinary oxalate, and recent research found that even a 20-fold increase in dietary oxalate can be compensated by adding more calcium. Vegetable fibre is protective.
Protein: the meat of the matter
A low-protein diet was once also considered a prophylactic for kidney health. However, recent research suggests that too little protein does you no good, and it is rather the intake of animal protein, especially meat, as opposed to overall protein, that makes for trouble. However, if you have uric acid stones, avoid purines—in beer and other alcohol, yeast, tinned fish, poultry, organ meats, legumes, leafy greens, cauliflower, tomatoes, asparagus.
Milk vs calcium
What about milk products which include calcium, a component of most kidney stones? Many people are at risk of premature bone loss, vitamin D insufficiency, or both. This means they should avoid cutting down on calcium (calcium binds with oxalates and prevents their absorption in the first place).
Sugar and salt and all things nice…
…seem to be bad news for your kidneys. Fructose, a fruit sugar, increases your chances of getting both kidney stones and gout. That’s not a concern for most people because the fructose present naturally in fruits and vegetables is modest. It becomes a problem, though, if you are predisposed to kidney trouble or the fructose is in a concentrated form: Colas and other processed foods largely credit the infamous HFCS (high fructose corn syrup) for their intense flavour.
Salt doesn’t help matters either. Recommendations are 2-3g a day, which is quite difficult if you eat any processed foods at all. However, high potassium helps, so many low-sodium salts can boost the taste stakes.
This column should not be considered a substitute for medical advice. The writer is a deputy features editor at Mint.
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