Inside the astonishing rise in kidney stones in seemingly ‘fit and healthy’ patients – as experts reveal why the trendy diet with too much PROTEIN could be to blame

Weeks before her daughter’s wedding, Sarah Wolfensohn noticed the tell-tale waves of colicky pain building in her left side and lower back.

With a familiar sense of dread, she knew it was a flare-up of her kidney stones – but this time worse than ever, as she was peeing blood too.

Kidney stones are small, hard lumps of salts and minerals such as calcium that can be otherwise symptomless until they move into the ureter – the tube carrying urine from the kidney to the bladder, where they cause excruciating pain. If they become lodged there, it can be life-threatening.

Sarah has suffered 14 attacks over the past 34 years – and says the pain is worse than childbirth, ‘so every time I get a twinge in my side or my back, I fear the worst’. Her most recent attack was a few months ago.

As dehydration can contribute to stones, she ‘drinks so much water that I’m always running to the bathroom’.

Yet despite this she’s ended up in hospital multiple times – ‘and it’s not pleasant,’ says Sarah, 71, a veterinary science academic and mother of two, who lives in Oxfordshire with her husband Simon, 73, a retired vet.

Kidney stones affect around one in 11 people at some point, and often recur. And now new research suggests they are becoming increasingly common.

Hospital admissions for kidney stone treatment rose by 27.4 per cent in England, and 17 per cent in Scotland between 2020 and 2025, according to a recent study published in the British Journal of Urology.

The researchers predicted a further 33 per cent increase by 2034-35 – as well as the personal cost to the individual patients, they predicted the cost to the NHS as £1.82billion and described the trend as ‘a growing burden’.

Men are roughly twice as likely as women to develop kidney stones – possibly because higher testosterone increases production of a natural compound called oxalate in the liver, which then binds with calcium to form calcium oxalate stones.

As well as rising cases generally, some experts say the demographic affected is changing.

Vimoshan Arumuham, a consultant urological surgeon at University College London Hospital, says he is increasingly seeing younger patients, including children – while the gap between men and women appears to be narrowing.

‘Usually, the drivers behind kidney stones are the same ones behind rising obesity and type 2 diabetes: diets high in salt, sugar and ultra-processed food and not drinking enough fluid,’ he says.

‘But I am now seeing patients who are fit and health-conscious – who develop kidney stones due to high-protein or carnivore diets – or they may be taking protein supplements.’

As he explains: ‘Eating a lot of protein makes urine acidic, raising the amount of uric acid in it but also increasing calcium (partly because the acid leads to calcium being released from bone), and lowers citrate, a stone inhibitor (found naturally in the body). This means stones form more easily.’

Research confirms this – with higher intakes of animal protein associated with an increased risk of kidney stones, reported Advances in Nutrition in 2022, in a review of 14 studies involving more than 100,000 people. Eating more meat and meat products was linked to a 22 per cent higher risk, while every additional 100g of red meat a day was associated with a 39 per cent higher risk.

Meanwhile, a study published in Urology in January which looked at protein shakes made from whey, pea, soy and rice found that whey protein – derived from milk – led to higher calcium levels and more acidic urine.

Mr Arumuham stresses there isn’t just one cause of kidney stones; it’s a combination of diet, genes, the anatomy of the urinary system (for instance, narrowing within the kidney’s drainage system can mean urine doesn’t drain as well) and dehydration.

Indeed, dehydration remains the biggest culprit as it makes urine more concentrated which encourages stones to form.

Most stones smaller than 5mm pass naturally, but those measuring 7mm or more don’t (partly because the ureter is usually only around 3mm wide).

‘The largest stone I have encountered was the size of a fist,’ says Mr Arumuham, who is also based at The Harley Street Clinic in London.

These bigger stones can become lodged, blocking the flow of urine. The most common symptom is extreme pain – it is often described as waves of throbbing or stabbing pain travelling from the side or lower back into the abdomen and groin.

‘In a way it’s similar to labour, as you are trying to squeeze something out of a tube that is too small,’ explains Professor Sarah Howles, an honorary consultant urological surgeon at the Churchill Hospital, Oxford, who co-leads the Oxford Stone Group research project. ‘I’ve asked lots of women if it’s equivalent to labour pain – and they say it’s worse.’

It can also lead to blood in the urine, as jagged stones scratch the lining of the urinary tract.

The most serious risk is if a stone blocks the ureter and infection builds up behind it – this can lead to sepsis. Complications from kidney stones cause around 130 deaths a year, according to the Royal College of Surgeons.

Repeated attacks can have consequences, too, explains Fiona Loud, policy director of Kidney Care UK: ‘Each recurrence roughly doubles the likelihood of progression to chronic kidney diseases.’

Treatment depends on the size and location of the stone.

The most common is lithotripsy, where shockwaves are applied through the skin to break up the stone. If this doesn’t work, then ureteroscopy, where a tiny telescope is passed up the urinary tract, can be used to locate and remove or break up the stone.

Larger stones may require an operation via a small incision in the back to access the kidney and remove them.

Sarah knows all too well how complicated treatment can become.

Her first attack, in 1990, caused such intense pain that she vomited. The stone eventually passed naturally.

Two years later, another stone became lodged in her ureter and required lithotripsy.

Doctors said the cause of her kidney stones was hypercalciuria, where her kidneys were releasing too much calcium into her urine.

‘I was prescribed diuretics [water pills], to increase my urine output so I pee out any small stones, but I found it hard to live a normal life on them as I was always rushing to the loo – so I stopped taking them,’ recalls Sarah.

Her most dramatic attack came in 2015, shortly before her daughter’s wedding. The stone was a huge 14mm. She underwent lithotripsy, but Sarah was back in hospital days later as fragments of the stone had blocked her ureter.

‘A tube was inserted into my bladder and a stent [a tiny tube-like structure] was put in to dilate the ureter to let fluid drain and remove the stone,’ says Sarah.

So what can you do to prevent kidney stones?

Advice depends on the type of stone – which is why patients are often asked to collect one if it passes so it can be analysed.

Typically, stones are formed of calcium oxalate. While the body produces oxalates naturally, certain foods, including spinach, nuts, soy products, chocolate and strawberries, are high in them – patients are advised to avoid these and to drink no more than two to three cups of tea (which also contains oxalates) a day.

Whatever the type of stone, the advice is to limit salt to 6g a day (salt increases calcium in urine); eat more fibre (which lowers the amount of calcium in urine); and drink plenty of fluids.

But contrary to what many people assume, cutting out calcium-rich dairy is not recommended – this can actually increase the risk of stones by raising oxalate levels in urine.

And now scientists are investigating a surprising potential culprit: bacteria. A recent study by the University of California revealed stones are embedded with bacterial biofilms – communities of bacteria protected by a slimy coating.

‘This is exciting research because it suggests bacteria may contribute to the formation and growth of kidney stones,’ says Professor Howles.

This offers the future possibility of treatments to prevent them.

beatkidneystones.co.uk