In September 2001 Dawn Page, a mother of two and from Oxfordshire, consulted nutritionist Barabara Nash who was promoting 'The Amazing Hydration Diet.'
Nash advised her to drink an extra four pints of mineral water per day, in addition to the tea and other fluids she normally consumed.
The nutritionist also suggested she should cut salt out of her diet, and begin eating gluten-free and wheat-free products.
But less than seven days later, Page began suffering with stomach cramps and sickness.
She contacted Nash about the side effects, but was assured that vomiting was part and parcel of the detox programme.
She was also asked to increase the amount of water she drank, and eat less foods containing sodium.
But on October 2 2001, Page collapsed in the family home with a Grand Mal epileptic fit - the most serious seizure known.
She was rushed to Princess Margaret Hospital in Swindon where doctors diagnosed a shortage of plasma sodium levels.
The salt-rich plasma acts as a cushion around the brain and, because it contained such low levels, allowed water to enter the brain itself, causing permanent damage. The doctors couldn't do much.
The former conference organiser was forced to quit her job and suffers frequent mood swings. She has relied on her husband Geoff, 54, for help ever since.
She now suffers from a range of other cognitive side effects which, her husband says, have 'changed her personality.' Her memory, concentration and the ability to speak normally, have all been affected badly.
Last week Page secured a £810,000 payout from Nash's insurance company following a six-and-a-half-year legal battle, Daily Mail reports.
The High Court in London ratified the settlement, which was made without mention of liability, at a hearing Friday.
Dawn's husband said she was not obese or even mildly obese but, like a lot of women, she only liked to look after her weight and was not having much success with the normal ways of doing that.
And she fell into the diet trap. 'She can't drive, can't work, and takes medication everyday. And she will do for the rest of her life.
'It has been like losing somebody, but not losing somebody. My wife was a very bubbly and outgoing person. She is nowhere near that now.'
The settlement reflected the seriousness of his wife's injuries, he said and warned others of the dangers of 'fad-type' diets.
Nash, who is based in Wheatley, Oxfordshire, has a diploma of natural nutrition gained from the College of National Nutrition in London. She describes herself a 'nutritional therapist and life coach' and denies any fault on her part.
Plexus Law, the firm which represented Nash in court, released a statement after the hearing, which read: 'On behalf of our client, we wish to make it clear that all allegations of substandard practice made on behalf of Mrs Page in the litigation, have always been and continue to remain firmly denied.
'In our view as a recognition of this, the settlement amount agreed to be paid was less than half of the total amount claimed and the compromise which was offered and accepted was on the basis of no admission of liability.
'As far as we are concerned, the case has now been concluded.'
Hydration diets are sometimes prescribed to those suffering from fluid retention, which can cause weight gain in the fingers, ankles and legs.
Fluid retention can be caused by the kidneys not working properly and it is thought some nutritionists claim additional water can 'kick start' the kidneys.
Registered dietician Nigel Denby said: 'If hydration ever leads to weight loss, it is simply because the extra water makes you less inclined to eat because you feel full.
Hydration diets do not work. I have no idea what the reduction of sodium is supposed to achieve, but no qualified professional would recommend this sort of diet.'
A serious loss of sodium can lead to weakness, dizziness, memory loss and nausea.
If the deficiency becomes severe, the circulatory system can collapse and the body can go into shock, causing fatigue, muscle twitching and fits.