Canola is generally considered a healthy oil thanks to its ability to reduce LDL cholesterol in the blood and lower the risk of heart disease. A new animal study out of Temple University, though, has shown that the vegetable-based fat increases substances in the brain that can lead to Alzheimer's disease.

"Canola oil is appealing because it is less expensive than other vegetable oils, and it is advertised as being healthy," explained study senior author Domenico Praticò, director of the Alzheimer's Center at Temple's Lewis Katz School of Medicine. "Very few studies, however, have examined that claim, especially in terms of the brain."

So the researchers set out to work with mice that had been engineered to contract Alzheimer's disease in the same way the condition affects humans: asymptomatic in early life and full-blown cognitive impairment when the rodents aged. At six months of age, when the mice still had no symptoms, they were split into two groups. One group was given a normal diet while the other had a normal diet plus the addition of approximately two tablespoons of canola oil each day.

Six months later, maze tests revealed the mice on the canola diet showed a decline in their working memory capacities compared to the other group. The canola-oil group also had gained a fair bit more weight than their non-oil-eating studymates.

The decline in cognitive function in the group of mice fed the oil-rich diet also corresponded to chemical changes in the brain. The canola-oil group showed a decrease in the levels of a protein known as amyloid beta 1-40. Amyloids are well-known in Alzheimer's research as the substances that form sticky clumps in the brain. But amyloid beta 1-40 actually helps prevent those clumps from forming by buffering amyloid beta 1-42, an insoluble form of the protein, so a reduction isn't a good thing.

As a result, in the brains of the mice that were on the oil-rich diets, an increase in amyloid plaques was noted with the substances wrapping around neurons, decreasing the number of contacts between them and pointing to serious synapse injuries. As synapses – the space between neurons where chemical signals are transmitted – are key to memory functions,the findings fit with the decreased ability the mice demonstrated in running the maze.

"Even though canola oil is a vegetable oil, we need to be careful before we say that it is healthy," Praticò said. "Based on the evidence from this study, canola oil should not be thought of as being equivalent to oils with proven health benefits."

One such oil is olive oil, which Praticò and his team showed could actually reduce amyloid plaques in mouse models in a study earlier this year.

The next step for the researchers is to conduct studies over a shorter period of time to see just how quickly Alzheimer's-disease-affected brains begin showing the damage. Even though the study showed no impact from canola oil on other disease-related markers such as inflammation or tau – another protein linked to Alzheimer's – the researchers say they will also delve into the role the fat might play in other conditions.

"We also want to know whether the negative effects of canola oil are specific for Alzheimer's disease," Dr. Praticò concluded. "There is a chance that the consumption of canola oil could also affect the onset and course of other neurodegenerative diseases or other forms of dementia."

The research has been published in the journal Nature.

Source: Temple University via EurekAlert