Giving mice with Alzheimer’s a canola oil-rich diet for six months led to their memory and learning ability worsening, a study reports.
The research, “Effect of canola oil consumption on memory, synapse and neuropathology in the triple transgenic mouse model of Alzheimer’s disease,” was published in the journal Scientific Reports.
Claims that the rapeseed extract canola oil is good for health, particularly the heart, has led to a jump in its consumption in recent years. But little research has been done on whether the claims are true.
“Canola oil is appealing because it is less expensive than other vegetable oils, and it is advertised as being healthy,” Dr. Domenico Praticò, an Alzheimer’s expert at Temple University’s Lewis Katz School of Medicine, said in a press release. “Very few studies, however, have examined that claim, especially in terms of the brain.”
Pratico’s team used a mouse model of Alzheimer’s to investigate canola’s effect on the formation of two harmful brain structures — amyloid protein clumps and twisted masses of proteins known as neurofibrillary tangles. Scientists have connected the two with the nerve cell degeneration and memory loss in Alzheimer’s.
The mice displayed the human features of Alzheimer’s, and their condition deteriorated with age. When they were six months old, researchers divided them into two groups. They fed one group a normal diet and the other a diet supplemented with a tablespoon of canola oil a day.
Six months later the team saw marked differences between the groups. Mice on the canola-rich diet were fatter and had impaired working and short-term memory and less ability to learn.
Significant differences in amyloid protein clumps and tangles, however, were not recorded between the two groups. “No significant effect of the canola oil-rich diet was found on some of the major protein systems in place to control Aβ [amyloid-beta] clearance and degradation,” the researchers wrote. “By the end of the chronic treatment, levels of total soluble tau and different phosphorylated isoforms were undistinguishable between the two groups, suggesting that canola oil does not influence tau metabolism.“
But the brains of the canfola-fed mice showed greatly reduced levels of a healthy form of amyloid protein — amyloid beta 1-40.
“Amyloid beta 1-40 neutralizes the actions of amyloid 1-42 [an Aβ peptide associated with neuronal loss and memory deficits], which means that a decrease in 1-40, like the one observed in our study, leaves 1-42 unchecked,” Pratico said. “In our model, this change in ratio resulted in considerable neuronal [nerve cell] damage, decreased neural contacts, and memory impairment.”
When nerve cells become trapped in amyloid beta 1-42 plaque, there are fewer synapses, or contacts between nerve cells, which leads to memory impairment.
A previous study showed that mice with Alzheimer’s that ate a diet rich in extra-virgin olive oil had lower levels of amyloid plaque, another biomarker of the disease known as phosphorylated tau protein and better memory.
The Temple findings suggested that eating a lot of canola oil can decrease brain functioning.
“Even though canola oil is a vegetable oil, we need to be careful before we say that it is healthy,” Pratico said. “Based on the evidence from this study, canola oil should not be thought of as being equivalent to oils with proven health benefits.”
The Temple researchers now hope to determine the minimum exposure to canola oil that can cause detrimental brain effects.
“We also want to know whether the negative effects of canola oil are specific for Alzheimer’s disease,” Pratico said. “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 study concludes: “our investigation demonstrates for the first time to the best of our knowledge a negative effect of the chronic consumption of canola oil on memory, synaptic integrity and Aβ 42/40 ratios in a mouse model of AD. The translational value of our findings lies in the observation that this type of oil supplementation can influence some of the most important features of the AD pathological phenotype.“