New research associates the consumption of canola oil with worsened memory, worsened learning ability, and weight gain in a mouse model of Alzheimer's disease. Results from the study were published yesterday in Scientific Reports. 

"Canola oil is appealing because it is less expensive than other vegetable oils, and it is advertised as being healthy," explained Domenico Praticò, M.D., professor in the departments of pharmacology and microbiology and director of the Alzheimer's Center at the Lewis Katz School of Medicine at Temple University (LKSOM), as well as senior investigator on the study. "Very few studies, however, have examined that claim, especially in terms of the brain."

Curious about how canola oil affects brain function, Dr. Praticò and Elisabetta Lauretti, a graduate student in Dr. Pratico's laboratory at LKSOM and co-author on the new study, focused their work on memory impairment and the formation of amyloid plaques and neurofibrillary tangles in an Alzheimer's disease mouse model.

Dr. Praticò and Lauretti had previously used the same mouse model in an investigation of olive oil, the results of which were published earlier in 2017. In that study, they found that Alzheimer mice fed a diet enriched with extra-virgin olive oil had reduced levels of amyloid plaques and phosphorylated tau and experienced memory improvement. For their latest work, they wanted to determine whether canola oil is similarly beneficial for the brain.

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The researchers started by dividing the mice into two groups at six months of age, before the animals developed signs of Alzheimer's disease. One group was fed a normal diet, while the other was fed a diet supplemented with the equivalent of about two tablespoons of canola oil daily.

The researchers then assessed the animals at 12 months. One of the first differences observed was in body weight—animals on the canola oil-enriched diet weighed significantly more than mice on the regular diet. Maze tests to assess working memory, short-term memory, and learning ability uncovered additional differences. Most significantly, mice that had consumed canola oil over a period of six months suffered impairments in working memory.

Examination of brain tissue from the two groups of mice revealed that canola oil-treated animals had greatly reduced levels of amyloid beta 1-40. Amyloid beta 1-40 is the more soluble form of the amyloid beta proteins. It generally is considered to serve a beneficial role in the brain and acts as a buffer for the more harmful insoluble form, amyloid beta 1-42.

As a result of decreased amyloid beta 1-40, animals on the canola oil diet further showed increased formation of amyloid plaques in the brain, with neurons engulfed in amyloid beta 1-42. The damage was accompanied by a significant decrease in the number of contacts between neurons, indicative of extensive synapse injury.

"Amyloid beta 1-40 neutralizes the actions of amyloid 1-42, which means that a decrease in 1-40, like the one observed in our study, leaves 1-42 unchecked," Dr. Praticò explained. "In our model, this change in ratio resulted in considerable neuronal damage, decreased neural contacts, and memory impairment."

The findings suggest that long-term consumption of canola oil is not beneficial to brain health. "Even though canola oil is a vegetable oil, we need to be careful before we say that it is healthy," Dr. 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."