It's one of the first times that solid evidence has been produced to dispute the health claims of the oil's manufacturers, although there have been concerns that it causes kidney, liver and neurological problems.
Now researchers from Temple University Health System have discovered that the oil creates plaques and tangles in the brain that are associated with Alzheimer's disease and other cognitive problems like learning difficulties and memory loss.
By comparison, the same research team discovered in an earlier study that extra-virgin olive oil actually reduces the levels of amyloid plaques in the brain, and helped improve memory.
For their latest research, the researchers used two groups of mice, one of which was fed a normal diet and the other was also given the equivalent of two tablespoons of canola oil a day. After a year, the canola-oil group was much heavier, and they failed memory and learning tests. On examination of their brains, the researchers discovered far higher levels of plaques, which prevented neurons from communicating.
Although canola is a vegetable oil, it is one that is mainly genetically modified in the US, and is used in many packaged and processed foods.