Why can bears get fat without getting sick? Biotech company Amgen is trying to answer that question, hoping to help humans who suffer from diseases like heart disease and diabetes. WSJ's Jonathan Rockoff reports.

JUST a week's bingeing on a high sugar and fat diet could damage your memory - and you may not get it back if you start eating healthy again.

New research has shown sugar alone may be the culprit in the memory deficit.

"What is so surprising about this research is the speed with which the deterioration of the cognition occurred," says Professor Margaret Morris from the University of NSW School of Medical Sciences.

"Our preliminary data also suggests that the damage is not reversed when the rats are switched back to a healthy diet, which is very concerning," she said.

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Rats were fed a variety of diets in the research including a "cafeteria diet" of fat, cakes, biscuits and a 10 per cent sugar solution.

These rats performed worse in memory tests as did those who ate a healthy diet but who were given access to sugar water to drink.

The tests showed the rats spatial memory was affected by the high sugar diet, however their ability to recognise objects was not affected.

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The tests on the rats also showed they had inflammation of the hippocampal region of the brain, which is associated with spatial memory.

The change in their memory occurred even before the emergence of weight increases.

The hippocampus is important in all sorts of memory and learning tasks in humans, Professor Morris says.

"We suspect these findings may be relevant to people.".

When a separate study published two years ago fed a group of humans a junk food diet for five days it found their reaction times were impaired and there was a deficit in their higher order processing of information.

This is one of the first studies that has separated out the effect of dietary fat and dietary sugar on the brain.

In the western diet fat and sugar tend to go together because they are blended in cakes and biscuits.

"It is certainly true our data looks like sugar alone is causing the deficit," Professor Morris said.

Initial observations in rats suggest that the memory deficit caused by the high sugar diet persists even when the rats go back to eating a healthy diet but Professor Morris says more research needs to be done.

Further research being conducted at the university will test what happens to the rats left on a cafeteria diet for three months.

Researchers also want to check if increasing exercise in the rats can preserve the brain even when they are on a high fat, high sugar diet.

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