Canola oil causes Alzheimer’s disease? Dubious evidence

Food fads make me want to scream, cry, and hide in a cabin in the mountains. MSG is safe. And high fructose corn syrup is just an awful name for sugar. And only a small number of people have a real gluten sensitivity. And now a new paper has caused the internet to explode with the trope that canola oil causes Alzheimer’s disease.

This new internet meme is based on a peer-reviewed article published in a real journal. But as I have written time and again, just because an article seems like it has sterling credentials, it doesn’t mean the article is above criticism. We’ll get to this article below.

As expected, all of the usual suspects in the pseudoscience world have jumped on board with clickbait headlines like, “Scientists finally issue warning against canola oil: Study reveals it is detrimental to brain health, contributes to dementia, causes weight gain.” I always find it ironic when a pseudoscience pushing website believes in scientists when it supports their belief.

Of course, we need to take a look at this whole issue. Here’s my spoiler alert (but please read the whole article) – there is little evidence that canola oil causes Alzheimer’s disease (AD) or dementia. You can use it safely.

What is canola oil?

I never really thought about it before, but when writing this article, I was wondering what the “canola” plant was. I know that corn oil comes from corn. And olive oil comes from olives. But I had never heard of the “canola.”

Canola oil is derived from rapeseed, the seeds of any of several plants from the Brassicaceae family. Rapeseed is an “oil seed” which was first used as a fuel for over 4000 years. Now the name, “rape,” doesn’t  derive from the violent act, but from the Latin word, rapum, which means turnip. Cabbages, mustard, Brussels sprouts, broccoli, and turnips are all related plants with that distinctive sulfurous flavor.

During World War II, rapeseed oil became an important lubricant for steam-powered marine vessels, because it clung to metal even in moist environments. During the war, the sources of rapeseed oil were mostly in Asia and Europe, which were disrupted by the war.

As a result, Canada jumped in and became the leading producer of rapeseed oil for Allies, with vast swaths of farming acreage in the Canadian provinces of Alberta, Manitoba, and Saskatchewan converted to rapeseed production. Of course, the war ended, and demand for the oil dropped.

At this time, rapeseed oil was not a popular choice for foods. First, it had distinctive taste as a result of the glucosinolates, the chemical that gives that sharp flavor to mustards, cabbage, and other cruciferous vegetables. Second, one of the constituent oils in rapeseed oil is erucic acid, which can be toxic at high levels. And finally, the oil has an off-putting greenish color as a result of chlorophyll (which probably doesn’t harm anyone).

So rapeseed growers looked into how they might continue to grow the plant and open new markets, especially as a food product. In the early 1970s, researchers at the University of Manitoba developed a cultivar of rapeseed that produced an oil that lacked the three negative characteristics of the industrial version of rapeseed oil. There have been further genetic modifications of the rapeseed plant to improve both flavor and qualities of canola oil since then.

Because of the unfortunate name and the lack of popularity as a food oil, the Rapeseed Association of Canada trademarked a new name for the oil. It was a condensation of “Can” from Canada and “ola” from other vegetable oils. You now know how to ask the proper question on Jeopardy if this ever comes up.

What does this have to do with the question of whether canola oil causes Alzheimer’s disease? Not much, although the chemistry of the oil is what is claimed to be at issue with the neurodegenerative diseases.

Alzheimer’s disease

Before I proceed, it’s important to describe Alzheimer’s disease. AD is a chronic neurodegenerative disease that usually starts slowly and worsens over time. It accounts for 60-70% of dementia cases, even though the terms are sometimes used interchangeably. Amyloid plaques and neurofibrillary tangles are generally easily visible by microscopic analysis of brain tissue from autopsies of those afflicted by AD. These plaques and tangles seem to have an effect on nerve functioning. Despite these observations, the precise pathophysiology, or development, of the disease is not known.

The causes of AD are unknown (notice how much we do not know about this disease), although it is speculated that it is mostly genetically-related, with a large number of genes that underlie this relationship. There is no clinical evidence that canola oil causes Alzheimer’s disease. And no, despite the internet tropes, there is no rigorous evidence that aluminum causes AD – I really wish this belief went away fast.

And since we have no clear understanding of the etiology and pathophysiology of AD, there really are no treatments available today for the disease. There are a couple of medications that help manage some of the symptoms of the disease, they are certainly not cures. There are several drugs at the very earliest stages of development that may hold out hope to actually treat the underlying disease.

The paper – a 10,000 meter level analysis

The study, published in Scientific Reports in December 2017, from Elisabetta Lauretti and Domenico Pratico of Temple University, was based on epidemiological observations that Mediterranean populations have a lower incidence of Alzheimer’s Disease (AD) compared to other populations. One of the hypotheses was that olive oil in the Mediterranean diet might contribute to a protective effect against Alzheimer’s disease. However, there is no robust evidence of a causal link between olive oil and a lower risk of AD. It is possible that the population level observation may be explained by genetic differences between Mediterranean populations and others.

Interestingly, modern canola oil has a similar chemical composition as olive oil, though it is comparatively less expensive. The authors hypothesized that canola oil protected against Alzheimer’s disease as much as olive oil.

This study analyzed mice that were genetically engineered to develop amyloid plaques and neurofibrillary tangles – as a result, these mice succumb to memory issues similar to humans. Six-month-old mice were fed either mouse chow or the same food plus canola oil for six months. The mice then underwent memory tests, and then sacrifice for a brain analysis.

As I’ve written before, animal studies are a very early stage of clinical research, and most early-stage biomedical research, around 90%, is a failure. So, even if this research, we are years away from making any conclusions about canola oil.

Otherwise, the authors, Lauretti and Pratico, are well-published researchers in various aspects of AD, and are affiliated with Alzheimer’s Center at Temple University, Department of Pharmacology Lewis Katz School of Medicine, a respected AD research institution. Unlike some vaccine researchers, Lauretti and Pratico are good scientists doing good research in AD.

Other than being a mouse study, which does not get me excited scientifically, it is difficult to criticize this study at the meta level. But it’s time to get into the rapeseed weeds of this article.

Does the article say canola oil causes Alzheimer’s disease?

Before I get to a critique of the research, let’s make one thing clear – the authors made no such claim. Even if they did, I would be concerned about their research with weak results.

First of all, the mice showed just a slight difference in one behavioral test. The researchers attempted three different memory tests, and the mice that consumed the canola oil only showed about a 20% difference in behavior to the control mice. And, that difference only showed up in only one test.

In the other two memory tests, the behavior of the canola oil mice was equivalent to the non-oil mice. Despite this unremarkable data, the authors claim it as “significant deficits of working memory.” I then re-read the data and discussion to see if I missed anything. I did not. The data simply does not indicate even a minor deficit in memory, let alone a “significant” one.

These results right here make me dismiss this study, almost without further review. If you want to claim that an animal model is supposed to represent what happens to humans, and very little is observed, I begin to doubt that we have anything close to a claim that canola oil causes Alzheimer’s disease.

Furthermore, the mice were fed really high levels of canola oil – so much so that the oil-consuming mice were about 20% heavier than the control group. I always worry about confounding factors in these type of studies, and obesity can cloud the results, since there is some weak evidence that obesity is related to AD. 

But there’s more.

The authors did not find any significant differences between the oil-consuming and control groups for beta-amyloids, which are responsible for the amyloid hypothesis, which claims that these amyloids may be the fundamental cause of AD by suppressing neuronal function. Although the amyloid hypothesis has not been fully supported by convincing evidence, it is important in making claims about whether canola oil causes Alzheimer’s disease.

As we have seen in other papers that try to analyze protein analysis, there can be significant variability in results even from the same animal. And in this paper, we see it again. Worse yet, they only performed a protein analysis or beta-amyloid on four mice in each group. With such high variation in results for each of the mice, and there were only four of them, it would be nearly impossible for me, as a scientist, to accept their results.

The researchers also looked at other biochemical markers of AD in these mice. This is what they found:

  • Tau protein. These proteins cause the neurofibrillary tangles that might be the cause of AD. In this study, they found no difference in levels of Tau protein between the oil-consuming and control mice.
  • PSD-95 protein. Decreased levels of this protein are associated with AD. This study actually showed lower levels of PSD-95 protein for oil-consuming mice.
  • Other protein markers. The researchers looked at GFAP and IBA1 proteins which are associated with neurological damage, and they found no difference between the groups. They looked at CREB, a transcription factor that is associated with AD, and found no difference. They looked at specific autophagy proteins, which break down certain proteins that may be associated with AD, and found no difference.  I think you might be seeing a pattern here.

Based on the small differences in one protein analysis (which itself had a lot of variation), along with the small difference in one of three different memory tests, it is hard for me to jump on board with a conclusion that canola oil causes Alzheimer’s disease.

In fact, the careful conclusion of the authors was:

Overall our findings do not provide support to some of the current ideas suggesting healthy benefits deriving from the regular consumption of canola oil. Although we recognize that more studies are needed to investigate the biological effects of this oil, our data would not justify the increasing tendency of replacing olive oil with canola oil as part of a good and healthy dietary alternative in non-Mediterranean countries.

Maybe I am missing something, but the researchers are saying that canola oil may not provide the same benefits as olive oil. They did not say that canola oil itself increased the risk of AD, which is what the popular press is claiming. This research is weak, but it’s not claiming what some individuals think they are claiming.

Canola oil causes Alzheimer’s disease?

This article neither claims that canola oil causes AD nor does it have any viable evidence to support that claim.

This leads me to other important issues this paper (other than the weak evidence and small sample sizes):

  • there should have been at least three groups, one that consumed normal mouse chow, one with canola oil, and a third with olive oil.
  • they should have controlled for obesity. Of course,
  • before anyone should buy into these type of studies, we need some sort of dose-response study. That is, if one level of canola oil causes Alzheimer’s disease, does a higher level of the oil cause a higher risk of AD.
  • I know these type of studies are expensive, but they need to have a much larger number of animals, especially for the brain protein analysis. The had only 22 mice for the behavioral studies, and I believe 8 for the protein analysis. I am used to clinical trials with thousands of patients, so this small number bothers me greatly.
  • we are cherry picking one animal study to come to some conclusion about the relationship between canola oil and Alzheimer’s disease. I could find no other clinical, pre-clinical, or epidemiological study that described evidence that supported a link.

Kevin Folta, Professor and Chairman in the Department of Horticultural Sciences at the University of Florida, about whom I’ve written several times, published a lengthy critical analysis of this research. His conclusion was interesting:

In my opinion the authors do oversell this a little in their conclusion. While they correctly state that there is a difference in amyloid 40/42 ratio, they also state “negative effect” on memory, which is shown as a statistically significant, yet minor effect on a single test. Other tests are consistent with their hypothesis of canola=no good, and their final statement of “our findings (in AD model mice) do not provide support to some of the current ideas suggesting healthy benefits deriving from the regular consumption of canola oil” does not say that the product causes dementia in humans.

The paper does not show in any way that there is a causal link to disease in humans. Not even close.

I’m going to go one step further than Dr. Folta. I don’t think they presented any robust evidence that canola oil is better or worse than olive oil with respect to the risk of AD. In fact, we do not have high-quality evidence that olive oil itself has any meaningful effect on the risk of AD, because all we have currently is an assumption that olive oil is the critical factor in Meditteranean populations for a lower risk of AD – we do not know this.

There is a lot of epidemiological data that their diet may be linked to a lower risk, but whether olive oil, pasta, fish, or cheese, we are a long way from knowing. But there are so many confounding factors, such as obesity (or lack thereof), tobacco smoking (much higher than in the USA), or something else, to make a claim that olive oil lowers risk of AD is speculative at best.

So is canola oil related to Alzheimer’s disease? Based on this study, no. Based on any other evidence we have, the answer remains no.

Citations



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The Original Skeptical Raptor
Chief Executive Officer at SkepticalRaptor
Lifetime lover of science, especially biomedical research. Spent years in academics, business development, research, and traveling the world shilling for Big Pharma. I love sports, mostly college basketball and football, hockey, and baseball. I enjoy great food and intelligent conversation. And a delicious morning coffee!