A woman who lost nearly three stone in 11 months suffered a brain illness normally associated with alcoholics.

Her condition mystified doctors because she insisted she was on a healthy, balanced, diet throughout.

Doctors say that either her own genetic makeup - or perhaps the herbal diet supplement she was taking might be to blame.

The 30-year-old, who was 11.5 stone before she began dieting, developed a condition called Wernicke's encephalopathy.

Wernicke's encephalopathy usually develops suddenly, and involves involuntary, jerky eye movements or paralysis of muscles moving the eye, coupled with poor balance, staggering gait or inability to walk.

When the condition, caused by a severe lack of vitamin B1, is diagnosed, doctors normally link it to heavy drinking.

This is because in chronic alcoholics, poor diet and frequent vomiting can deprive the body of the vitamin.

Not alcoholic

However, in this case, there were no alcohol problems.

The woman had been eating an apparently balanced - although calorie-controlled - diet, even including extra tablets of vitamin B1.

Instead, the finger of suspicion pointed at the herbal supplement she had been taking to alleviate hunger pangs during the 11 months.

Dr GianPetro Sechi, from the University of Sassari in Italy, said he believed that the herb might somehow interefered with the body's ability to take up vitamin B1, or thiamine, from the diet.

He said: "There is the possibility that a decreased intestinal absorption of thiamine, facilitated by the use of the herbal preparation, may have caused a deficiency of the vitamin in the patient."

If Wernicke's is left untreated, then permanent brain damage can occur.

Prompt treatment

However, in this case, immediate treatment - high doses of thiamine injected into a muscle - reversed the symptoms within days, and the patient apparently suffered no permanent damage.

Dr Mike Green, from Aston University, said that there was some evidence that dieting had an effect on mental function - but that the weight loss experienced by this woman was "not severe".

He said: "The symptoms are associated with starvation, but this woman's dieting is not that radical."

The case is reported in the journal Neurology.