Alzheimer's disease is shrouded in mystery but a new study has shed some light on one of its possible causes — a high-fat diet.

The research — conducted by the Veterans Affairs Health Care System in Seattle and published in Archives of Neurology — found that people who ate low-fat diets high in fruit and vegetables were far less likely to develop Alzheimer's than those who consumed lots of saturated fats.

In a four-week trial, people who ate a diet that was low in saturated fat and focused on low-glycaemic-index foods (e.g. whole grains, beans, vegetables) were shown to have decreased levels of B-amyloid 42, which is a protein that is a biomarker of Alzheimer's disease risk and is also associated with problem-solving ability and brain inflammation.

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However, a second group of test subjects, who were given a diet that was high in saturated fat and high-glycaemic-index foods (e.g. white bread and white rice), demonstrated not only unhealthy changes in their serum cholesterol and insulin levels, but also a striking effect on their concentrations of B-amyloid 42, which, according to the report's conclusion, "essentially moved them in a direction that may characterise a pre-symptomatic stage of Alzheimer's disease".

Study leader Dr Susan Craft adds, "A healthy diet that contains a lot of fruit and vegetables would be important for people who have Alzheimer's disease or conditions that put them at risk for developing Alzheimer's disease".

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