THE weight-loss revolution that has inspired millions of women to rise up against the temptation of carbohydrates in favour of a juicy steak with a side order of spinach or rocket may not be medically safe after all, a team of doctors says.

Whippet-thin converts of the Atkins diet could find that adhering to the excruciatingly boring rules of the ultrafashionable, high-protein, low-carbohydrate diet means facing the even more excruciatingly painful experience of kidney stones.

The Atkins diet, which inspires near-evangelical zeal in its converts, could be a “one-way ticket” to kidney stones, according to Dr Bill Robertson, a clinical biochemist at the Institute of Urology and Nephrology at University College Medical School in London, who has seen a marked increase in the number of patients with kidney stones. The soaring number of young women suffering from the traditionally male condition is of particular concern.

Dr Robertson and his team claim that the Atkins diet, which has challenged Harry Potter in book sales, could double the risk of kidney stones, a condition so painful that it is often compared unfavourably with the agony of giving birth. “If I was designing an experiment to make people form kidney stones, I’d put them on the Atkins diet,” Dr Robertson said.

Eating large quantities of meat, as extolled by the Atkins diet, is dangerous for two reasons, Dr Robertson said. Extensive research compiled by his team over the past 30 years has shown that high levels of animal protein substantially increase the amount of chemicals that form kidney stones, such as calcium in the urine. Eating large amounts of certain vegetables, such as spinach, can enhance that effect because of the amount of the kidney stone-forming chemical oxalate that they contain.

Living off a diet rich in animal proteins and oxalate constitutes “a double whammy as far as the threat of developing kidney stones goes”, Dr Robertson said. “It is the worst possible combination you can imagine. The absence of fruit and other vegetables in the diet means the body is deprived of a means of counteracting the negative effect. The high-protein diets have contributed to an increase in the number of kidney stones that we are seeing.”

Whereas, traditionally, one woman to every 2.5 men was afflicted by the condition, that figure has now risen to one woman to every 1.3 men.

The increase mirrors the changes in sexual behaviour among young women: because women are having sex younger and more frequently than in the past, they are more susceptible to urinary tract infections, such as cystitis, which can be brought on by sexual contact.

The antibiotics that are commonly prescribed to treat those infections deplete the body of the organism that normally insulates them against the development of kidney stones. As women are more likely than men to try to lose weight by dieting, their chances of developing kidney stones have soared.

Dr Robert Atkins first published his Atkins diet more than 30 years ago but it has only recently become a phenomenon, endorsed by converts as diverse as Senator Al Gore and Geri Halliwell, the former Spice Girl. When Dr Atkins died at 72 from head injuries in April after slipping on ice, his book had sold more than ten million copies.

A month later, his claim that his was a nutritionally safe diet (which bans fruit as well as bread, pasta and potatoes) was vindicated by two American studies.

Published in the New England Journal of Medicine, the studies put 132 men and women on the Atkins diet for a year and found that they lost an average of 9.5kg (21lb) in three months — almost twice as much as on conventional low-fat, high-carbohydrate diets — without any damage to their health. The studies even showed that, in the short term, the Atkins diet might actually help to combat heart disease and diabetes.

Until now, any evidence of the negative health effects of the Atkins diet has been negligible. One unconfirmed theory suggests that an Atkins-style diet might worsen osteoporosis.

Otherwise, the diet’s known side-effects are more socially problematic than health-threatening: constipation and bad breath caused by the process of ketosis (when fat is broken down by the body) is a small price to pay to drop a dress size, say Atkins disciples.

But how slick will that new slimline body look when rolling around on the floor in a fit of agony? Kidney stones are small, hard, chalky deposits that are formed in the kidney and which can become wedged in the ureter (the tube that drains urine from the kidney) as they are expelled. This temporarily blocks the tube, causing a spasm, and causes the kidney to swell much like a balloon filled with water. It is extremely painful and there are few warning signs: the first symptom of a kidney stone is often a sharp and unexpected pain so agonising that it causes the sufferer to collapse and vomit. If the stone is not expelled naturally, it can either be broken down by ultrasound or with a laser that is threaded up through the urinary tract. At worst, an operation might be necessary. A kidney stone can grow to the size of a fist.

The number of patients with this condition is increasing, Dr Robertson said. In Britain, 6 per cent of the population suffer from kidney stones by the time they reach their sixties. In the Middle East, where animal protein is consumed as frequently as three times a day, the figure is 15 per cent.

“There is no doubt that the diet is good for losing weight, but you have to think about the secondary effects,” said Dr Robertson.

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