A healthy diet, regular physical exercise and a normal body weight can reduce the build up of abnormal proteins that are associated with the onset of Alzheimer's disease, a study has concluded.

Researchers at UCLA's Semel Institute for Neuroscience and Human Behavior in the US studied 44 adults, ranging from age 40 to 85, who all had mild memory loss but no dementia.

Data on participants’ body mass index, levels of physical activity, diet and other lifestyle factors were collected. They also underwent a scan to measure the level of plaques and tangles in the brain.

The study found that each one of the lifestyle factors - a healthy body mass index, physical activity and a Mediterranean diet - were linked to lower levels of plaques and tangles on brain scans. A Mediterranean diet is rich in fruits, vegetables, legumes, cereals and fish and low in meat and dairy, and characterised by a high ratio of monounsaturated to saturated fats, and mild to moderate alcohol consumption.

Scientists are not 100% sure what causes Alzheimer’s but plaques and tangles are key indicators in cell death and tissue loss in the Alzheimer brain. Plaques are abnormal clusters of proteins called beta-amyloid that build up between nerve cells. Tangles form inside dying cells and are twisted fibres of a protein called tau.

In healthy areas, tau helps keep the transport system on track. But in areas where tangles are forming, the twisted strands of tau essentially disintegrate the transport system so that nutrients and other essential supplies can no longer move through the cells, which eventually die. Though most people develop some plaques and tangles as they age, those with Alzheimer’s tend to develop far more.

Earlier studies have linked a healthy lifestyle to delays in the onset of Alzheimer's. However, this study is the first to demonstrate how lifestyle factors directly influence abnormal proteins in people with subtle memory loss who have not yet been diagnosed with dementia, according to Dr David Merrill, the lead author of the study, which appears in September’s American Journal of Geriatric Psychiatry.

He said: “The study reinforces the importance of living a healthy life to prevent Alzheimer's, even before the development of clinically significant dementia. This work lends key insight not only into the ability of patients to prevent Alzheimer's disease, but also physicians’ ability to detect and image these changes.”

The next step in the research will be to combine imaging with intervention studies of diet, exercise and other modifiable lifestyle factors, such as stress and cognitive health, Merrill said.