A diet rich in omega-3 fatty acids, found in fish such as salmon and sardines and in fish-oil capsules, can help keep Alzheimer's disease at bay, a new Canadian study suggests.

The research, which was done on mice, provides the strongest evidence so far that a deficiency in a specific dietary component can have a direct impact on the risk of developing the devastating disease.

"If you have a diet that is poor in omega-3s, that will accelerate the process of Alzheimer's, especially if you're genetically predisposed," said Fridiric Calon, a molecular endocrinology researcher at the Laval University Medical Center in Quebec City.

A number of studies have suggested that people who eat a diet rich in fish are less likely to develop Alzheimer's and heart disease. Although the mechanism was unclear, the hunch was that it was due to omega-3s.

Omega-3 fatty acids have become so popular with health-conscious consumers that food manufacturers are adding them to products such as eggs and milk. The eggs are produced by feeding chickens a special diet of flaxseed, which is rich in omega-3. The milk is enriched with flaxseed oil.

The new Alzheimer's research, published in the medical journal Neuron, shows that one type of omega-3, called docosahexaenoic acid (DHA), seems to keep synapses healthy. Synapses are the chemical connections between brain cells that enable memory and learning.

The findings were serendipitous. Researchers were working with mice specially bred to develop an Alzheimer's-like disease but noticed the animals were not developing the expected neurological damage.

The researchers realized the diet the mice were being fed -- soy and fish -- was chock-full of omega-3s. So they started a new study, feeding one group of mice the soy and fish diet and a second group a diet of safflower oil devoid of omega-3 fatty acids. After five months, they dissected the rodents' brains.

"We found high amounts of synaptic damage in the brains of the Alzheimer's-diseased mice that ate the DHA-depleted diet," said study co-author Sally Frautschy, an associate professor of neurology at the University of California at Los Angeles.

The mice fed a diet poor in omega-3s also did poorly in memory tests, further evidence of brain damage.

Calon said that while the research does not provide the final answer, he believes that increasing the intake of omega-3s, and DHA in particular, likely offers some protection against Alzheimer's.