Mumbai (AFP) - Indian doctors put an Egyptian believed to be the world's heaviest woman on a special liquid diet Monday as they prepared her for an emergency weight-loss operation.

Eman Ahmed Abd El Aty weighs around 500 kilogrammes (1,100 pounds) and had not left her house in more than two decades until arriving in Mumbai at the weekend for bariatric surgery.

Doctors said the 37-year-old would be fed only liquid supplements for the next 25 days to help her lose the 50 kilogrammes required before they can begin operating.

"Only after all the diseases related to obesity are brought under control and Eman loses weight will we conduct the surgery," Dr Muffazal Lakdawala told reporters, adding the procedure would take two and a half hours.

The specialist weight-loss surgeon said he and his team at Mumbai's Saifee hospital hoped the surgery would help Abd El Aty shed another 150 kilogrammes.

It would allow her to sit up and feed herself, something not possible in her present state.

Following the surgery she will spend five months being closely monitored by the Indian specialists and receiving physiotherapy to exercise her muscles before returning to Egypt.

Lakdawala said if the initial treatment was successful then doctors could use surgery to bring Abd El Aty's weight down to under 100 kilogrammes in a couple of years' time.

The Egyptian, who hails from the Mediterranean port city of Alexandria, was flown to India's commercial capital in a specially modified Airbus on Saturday for treatment.

Abd El Aty's sister had approached Lakdawala in October, saying her sibling needed urgent medical attention.

Her family told the doctor that as a child she was diagnosed with elephantiasis, a condition that causes the limbs and other body parts to swell, leaving her almost immobile.

Abd El Aty has suffered a stroke and faced a series of other serious ailments owing to her weight including diabetes, high blood pressure, hypertension and sleep deprivation.

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Her request for an Indian visa was initially denied, but she was granted passage after tweeting a plea for help directly to India's foreign minister, who intervened.

Abd El Aty had a long wait as no airlines were willing to fly her due to her health complications.

Bariatric surgery is a stomach-shrinking bypass procedure carried out on those wanting to lose excessive weight.

It is increasingly common in India, which has a growing problem with obesity, particularly in urban areas.

India is a major destination for medical tourists seeking quality services and no waiting lists at a fraction of the cost of western countries.