Every month or two we receive a barrage of information telling us that a specific food is either good or terrible for our health. Red meat is bad; the peppers are good. Broccoli saves and destroys lives. If you want to live longer, make sure you eat blueberries, but wait, no those blueberries.
The most recent of these stories is about olive oil and it has been popping up everywhere. Apparently, olive oil is the key to preventing people from dying of dementia as they age. An extra half a tablespoon of refined fat per day could reduce your risk of dementia mortality by 28%!
Unfortunately for salad lovers (and bread lovers) everywhere, the truth isn’t quite as simple as that. It’s possible that olive oil is good for you, but chances are it’s just another interesting combination that doesn’t mean much in your life.
The research that got everyone excited about olive oil is a new nutritional epidemiology paper that looked at two large cohorts of people recruited and followed in the United States: the Nurses’ Health Study and the health professional follow-up study. The authors of the paper, which appeared in Nutrition, Obesity, and Exercise, looked at what these people reported eating, then compared the risk of dying from dementia over a 28-year period for people who reported eating plenty of olive oil (11 grams, or about a tablespoon per day) with those reporting eating less.
At the end of the study, researchers found that people who reported eating a lot of olive oil were less likely to die from dementia. The “results suggest that olive oil consumption represents a potential strategy for reducing the risk of dementia mortality,” they write.
According to nutritional epidemiology studies, this was not bad. The authors controlled for a range of factors in their analysis, such as whether participants reported smoking or having other health problems; they even controlled for other elements of their self-reported dietary intake. The researchers also performed a series of sensitivity analyzes to try to rule out other factors that could be causing these results.
And yet, I still don’t recommend you buy a gallon of olive oil. This type of study is, by definition, complex. Ultimately, it is very unclear whether olive oil leads to a lower risk of death from dementia or whether it is simply an association, despite the authors’ hard work.
Even taking the results at face value, olive oil is not a single substance. The article includes an analysis of the impact of replacing other fats with olive oil: if people in this cohort replaced mayonnaise in favor of using olive oil, it helped . But the study found that canola and sunflower oils had the same protective effect as olive oil.
Furthermore, and quite strangely, the authors show that olive oil does not have just reduce the risk of death from dementia. It also reduced the risk of dying in general. Why not praise these discoveries? It is relatively easy to understand how olive oil could probably help reduce the risk of death from dementia, thanks to compounds that could reduce inflammation in the brain. (I’m still skeptical, but it’s at least possible!) It’s much harder to know what connection this might have with breast cancer or suicide risk. This seems to be a reason to take the results with a grain of salt. The simplest explanation is that something else is going on with people who opt for olive oil, not that olive oil is a health elixir.
And the thing is, there are only so many things you can control in this type of study. For example, the authors did not actually have data on the wealth of the people participating in their study. This data was not collected in the 1970s and 1980s, when these two cohorts were created. To control for socioeconomic aspects, the authors instead used an area-level measure, which calculates an average score for the neighborhood where people lived, a statistic that can be quite misleading when dealing with individuals. Someone’s neighborhood can offer you a guess to the size of their bank account, but not much more.
Furthermore, people are really bad namely how much they eat of specific things. The dietary questionnaires that this type of research relies on are notoriously problematic: They ask participants to recall what they ate from all sorts of food groups over the past few months. This means that the measure of olive oil consumption cited by the authors may not accurately reflect the amount actually ingested by the individuals participating in the study. Unless you cook all of your foods and carefully measure and record every time you add olive oil, it would be very difficult to provide a researcher with an accurate picture.
You also need to take into account here the magnitude of the presumed effect. On average, over the decades these cohorts were followed, about 24 out of 10,000 people in the group who consumed no olive oil died each year from dementia. For the people who ate a lot of olive oil, which was reduced to 16 deaths per 10,000, or less than a tenth of a percentage point. This does not represent a significant reduction in risk.
Finally, and perhaps most interestingly, the benefits of olive oil were only visible to women. In the Nurses’ Health Study, which included only women due to the decade in which it began, there was a 33 percent relative benefit for consuming olive oil (although that this relative benefit always translates into a very small reduction in deaths compared to thousands of women). . In the health professionals’ follow-up study, which recruited men, no benefit was detectable for people who consumed more olive oil.
It is certainly possible that olive oil is good for your health. Of course, if the results of this study are to be believed, this is only true for women, and you can use other vegetable oils instead anyway.
What is much more likely is that olive oil is simply partner with generally better health. You can control in these studies the things you know and measure, but not the things you don’t know or can’t measure. These studies aren’t done by keeping people in a lab for 28 years: humans are complicated, and it’s basically impossible to interview them about every aspect of their lives and have them write it down accurately.
If you love olive oil, there’s no reason to stop eating it, but there’s also not much evidence that eating more will save your life. life.