Scientists are studying the ketogenic diet as a weapon against cancer

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Zoe Taylor had her first epileptic seizure in May 2013. It was the most frightening and painful experience of her life. 'I've had two children without pain relief and that was a breeze by comparison,' says Zoe, 33. 'It was a pain you can't imagine. It started in my tongue and I felt impelled to open my jaws as wide as possible. 'I expelled all the air from my lungs and then I couldn't breathe in.'

As well as feeling as if she was suffocating, her body was jerking uncontrollably, then she fell unconscious. After that, she had similar seizures every six weeks or so and smaller ones up to ten times a day. 'My jaw would go fuzzy and numb. Afterwards, I'd feel tired and get emotional about the smallest thing.' In July, the cause was revealed - a slow-growing brain tumour.

'I was told it might stay in the same state for years, but they wouldn't operate because its location meant I might suffer brain damage,' says Zoe, who lives with her husband Lee, 35, a hairdresser, and their children, Milo, four, and Isabella, seven, in Totnes, Devon.Unfortunately, leaving the tumour in place meant it could become aggressive.

'I was told radiotherapy might prolong my life by several years, but only half of patients who develop the aggressive type of tumour are alive a year later.' Conventional treatment for brain cancer involves surgery, if possible, and chemotherapy and/or radiotherapy, as well as epilepsy drugs for the seizures - these occur because the tumour presses on surrounding brain cells. Zoe is taking epilepsy drugs, but she believes their effect has been boosted dramatically by following a diet approved to treat children with epilepsy.

Known as the ketogenic diet, it is being used experimentally to help a few adult brain cancer patients control their seizures. It's thought it might even help tackle cancer.

Many cancer patients switch to a diet high in fruit and vegetables in the belief it can help them fight the disease. However, according to Professor Tim Key, of Oxford University's cancer epidemiology unit, the evidence for this sort of diet is 'weak'. But could the ketogenic diet be different?

The radical approach is being investigated at two university brain research centres. The diet involves cutting carbohydrate intake to a minimum - no more than an ounce a day. Out go pasta, rice, sugar, cakes and biscuits; fruit and vegetables are the main carbohydrates.

Patients eat generous amounts of fats, such as olive oil, butter and coconut oils, and normal amounts of protein - meat, fish and eggs. The idea is to keep carbohydrates low enough so the body starts producing ketones as an alternative energy source - these are produced by the liver from body fat.

This is a natural process and many of us have slightly raised ketone levels before breakfast because we've been fasting through the night. They have been found to have a calming effect on the brain. Indeed, ketogenic therapy is a recognised medical treatment for childhood epilepsy. About 30 per cent of epileptic children don't respond to drugs.

'Ketogenic therapy is used after randomised trials found 40 per cent of children had a 50 per cent reduction in their seizures,' says Susan Wood, a dietitian who specialises in ketogenic therapy. Extensive trials haven't been done on adults with epilepsy. The theory is 'almost too good to be true', says biochemist Dr Daniel Tennant at Birmingham University.

'Tumours are addicted to a high glucose supply, so a reasonable way to attack them is by cutting carbs, which lowers blood glucose, reducing their energy supply.' What's more, the ketones that the body produces to replace glucose as an energy source can be used by healthy cells, but can't be used by cancer cells.

'The ketogenic diet seemed such a plausible way to protect brain cells and starve cancer cells that we had to investigate it,' he says. A U.S. study on mice published in the Journal of Lipid Research found those on a ketogenic diet responded better to radiotherapy than those on a normal diet.

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Professor Adrienne Scheck, a neuro-oncologist at the Barrow Neurological Institute in Arizona, led the research. 'It looks as if the diet can have an effect on the way genes behave - it can help reverse processes that encourage tumour survival,' she says. It seems to reactivate a system that forces damaged cells to commit suicide.

A branch of Imperial College in London - the Molecular Neuro-oncology laboratory at Charing Cross Hospital - is also looking into ketones and cancer. One of its scientists, Dr Nelofer Syed, who studies the biochemistry of the brain, was intrigued by Professor Scheck's mice study. 'There is a possibility this diet could change the way tumour genes behave,' she says.

Zoe Taylor has been on a ketogenic diet for a year, helped by the Astro Brain Tumour Fund, which funds NHS dietitians to treat adults whose cancer is causing epilepsy. 'At first, it was challenging,' says Zoe. 'You have to cut out so many foods and eating out is almost impossible because everything contains carbohydrates.'

A typical breakfast is scrambled eggs and cream while dinner is fish curry with green peppers, coconut and watercress. 'But it's made such a difference. A month after I started, I felt a big seizure was coming, but it just fizzled out. I've had no major ones since and only a fraction of the mini-attacks.

'I'd been feeling dreadful for two years before the first seizure - I picked up any infection going around and had tonsillitis every six months. I used to have a brain fuzziness and that's gone. 'I'm brighter and more energetic.' She's also been told an operation to remove the tumour is now possible because it has shrunk.

'No one is saying the diet did it, but I think it made a difference,' she says. However, the diet is controversial, not least because it flies in the face of conventional advice. Dietitians are wary of recommending large amounts of fat, much of it saturated. There are also concerns that a high protein intake is unhealthy, with one major study linking it to a raised risk of heart disease. But the ketogenic diet used to treat epilepsy has normal levels of protein and high fat.

Kieran Clarke, professor of physiological biochemistry at Oxford, believes concern about the safety of increasing ketone levels is based on a misunderstanding. 'The ketone pathway developed as a way to provide animals and humans with energy in times of famine. 'It's only if someone has uncontrolled diabetes that raising your ketone level is dangerous.

'Today, people rarely need to switch to ketone production because we are surrounded by cheap carbohydrates. 'Before, many people would be making ketones for much of their lives.' Dr Tennant is leading a study at Birmingham University in which healthy volunteers on a low-carb, high-fat diet will be given MRI scans to track metabolic changes in the brain.

'We will be able to see the changes in the way cells use energy,' says Dr Andrew Peet, a paediatric oncologist involved in the research. 'We can monitor how fats and carbohydrates affect the rate of cell growth.' This is a new direction for cancer research which, for a decade, has been about targeting genes.

'That hasn't been as successful as we hoped because the target keeps moving as cancers keep mutating,' says Dr Peet. 'But that's not a problem if you can target the energy supply. This research could alter the way we think about the role of diet in treating cancer patients.' The hope is to start a trial with human volunteers within a year.

Charing Cross Hospital supports brain cancer patients who ask to go on the diet as well as have standard treatment. 'If a patient asks for the ketogenic diet to be part of a package that includes chemotherapy and radiotherapy, we will involve a dietitian to help them,' says consultant oncologist Dr Matt Williams.

Cancer Research UK has been cautious about possible benefits of any diets on cancer. However, Professor Key, its scientific adviser, says the ketogenic diet research is 'very interesting' and he 'looks forward to the results'.