The research by scientists at the Karolinska Institutet has revealed that mice fed a diet of junk food for a nine month period developed the abnormal brain tangles which are seen in the preliminary stages of Alzheimer's disease - they say a diet rich in fat, sugar and cholesterol could increase the risk of the most common type of dementia.

According to Susanne Akterin, a postgraduate researcher at the Institute's Alzheimer's Disease Research Center, who led the study, the diet caused a chemical change in the brains of the mice similar to that found in the Alzheimer brain.

Ms Akterin says this has led to the suspicion that a high intake of fat and cholesterol in combination with genetic factors can adversely affect several brain substances, which contribute the development of Alzheimer's.

Alzheimer's disease is the most common form of dementia among older people and is incurable - it affects the parts of the brain involved with thought, memory and language.

Alzheimer's disease is difficult to treat and new drugs focus on removing clumps of beta amyloid protein that forms plaques in the brain but researchers are also examining ways to deal with the toxic tangles caused by an abnormal build-up of the protein tau.

Akterin's research focused on a gene variant called apolipoprotein E (apoE4) found in 15 to 20% of people which is a known risk factor for Alzheimer's - apoE4 is also involved in the transport of cholesterol.

For the study mice were used which were genetically engineered to mimic the effect of the variant gene in humans which were then fed a diet rich in fat, sugar and cholesterol for nine months - meals with a similar nutritional content of fast food.

Akterin says the mice showed chemical changes in their brains, indicating an abnormal build-up of the protein tau as well as signs that cholesterol in food reduced levels of another protein called Arc involved in memory storage.

The change was an increase in phosphate groups attached to tau, a substance that forms the neurofibrillary tangles observed in Alzheimer ™s patients. - these tangles prevent the cells from functioning normally, which eventually leads to their death.

Previous research has shown that a phenomenon known as oxidative stress in the brain and a relatively low intake of dietary antioxidants can also increase the risk of Alzheimer ™s and Akterin's research shows that two antioxidants are dysfunctional in the brains of Alzheimer patients, which can lead to nerve cell death.

Akterin says the results give some indication of how Alzheimer's can be prevented, but she says more research needs to be done before appropriate advice can be passed on to the general public.