In a surprising study published in the scientific journal Lancet, researchers found that being fat in your middle age appears to reduce the risk of developing dementia, rather than increasing it. A study of two million people found that the underweight were far more likely to develop dementia, a growing problem for the elderly in the Western world.

According to the new study, underweight people had a 34 percent higher risk of developing dementia than those of a normal weight, while very obese people had a 29 percent lower risk of becoming forgetful and confused and showing other signs of senility.

Obesity levels, like dementia levels, have been skyrocketing across the western world and is becoming more and more a problem for health care systems in many countries. The new study flies in the face of previous smaller studies and the advice offered by modern medicine - what is good for the heart is good for the head. A study in 2008 of 6,000 people found that people who have big bellies in their 40's were much more likely to get Alzheimer's and dementia in their 70's. The study was one of the first to connect middle-aged spread to a fading mind.

But the new research "overshadows those (previous studies) by orders of magnitude," said Nawab Qizilbash of Oxon Epidemiology, who led the study. "We show completely the opposite," Qizilbash said. For the study, patients were an average of 55 years of age. Of the patients, 45,507 of them developed dementia over an average of nine years and the research found that the rates of dementia fell steadily as their weight rose.

"We did a lot of analysis to see if we could explain it but it just seems to persist. We couldn't get rid of it, so we're left with this apparent protective effect," the scientest was quoted as saying.

The co-author of the paper said the results suggested "that doctors, public health scientists and policymakers need to re-think how to best identify who is at high risk of dementia."

"If we can understand why people with a high body mass index have a reduced risk of dementia, it's possible that further down the line, researchers might be able to use these insights to develop new treatments," Stuart Pocock of the London School of Hygiene and Tropical Medicine said.

Qizilbash warned, however, that being overweight or obese brings with it a much higher risk of death from any cause and a higher risk of stroke and other diseases.

"So even if there is a protective effect against dementia from being overweight or obese, you're not living long enough to benefit from it."