What you probably didn't hear is that a study published in the British Medical Journal (BMJ) February of this past year found that though the first claim is true--swapping out saturated fats for vegetable oils will lower your cholesterol--if the oil you use instead of saturated fat is full of omega-6 fatty acid, like safflower oil or corn oil, the second claim is completely false.
The study found that when men who had already had a heart attack replaced saturated fats with safflower oil and ate margarine made with safflower oil they significantly raised the risk that they would die of a heart attack, stroke or, in fact, any cause of death, over the next five years.
How significantly was that risk raised? The study states: "Among the control and intervention groups combined, an increase of 5% of food energy from unspecified PUFA [polyunsaturated fatty acids] predicted about 30% higher risk of cardiovascular death and all cause mortality.
A reduction in SFA [saturated fat] and increase in the PUFA:SFA ratio were also associated with increased risks of all cause and cardiovascular mortality." In short, the more they replaced saturated fat with "healthy" polyunsaturated oil the more likely they were to die.
I was only made aware of this study last week, when the Canadian Medical Association Journal (CMAJ) published an opinion piece questioning whether the government should be putting "heart healthy" labels on corn oil and other polyunsaturated fats. (Details HERE.) They cited the February BMJ study in their write-up.
What doesn't come across in the small amount of press the CMAJ article got is something that makes the BMJ study even more significant: The data that this finding was based on was 40 years old. It was collected during the Sydney Diet Heart Study, a randomized controlled trial conducted in 1966-73.
This was one of the many landmark interventional studies whose result was used to convince doctors that replacing saturated fats with polyunsaturated fats would lower cholesterol and, by implication, prevent heart disease.
But while the authors of the original study published the finding that the polyunsaturated fats would lower both cholesterol and triglycerides, they did not look to see whether lowering cholesterol with this intervention actually helped prevent heart-related deaths.
They eventually admitted in a study published in 1978--a full 5 years after they began to publish their results--that there was a higher "all cause mortality" in the group eating the safflower oil, but they did not look at whether these deaths were from cardiovascular-related causes. This was a surprising omission, given the point of the dietary intervention--to lower cholesterol in order to prevent heart attacks.
So it was only in the last few years that a new group of researchers were able to go back to the original study's raw data and take another look at it. When they did so, they discovered what they term "previously missing data." This "missing data" was the data that led to the conclusion that there was a 30% greater risk of cardiovascular death among the people in the study who ate the cholesterol-lowering oil.
|Where the Smoking Gun Was Hiding|
Once they recovered the data, the researchers did a very careful analysis, teasing out other factors that might have affected the death rate and, most significantly, analyzing whether the transfat associated with the margarine the test subjects ate might have explained the higher death rate. They conclude it did not.
They also point out that this re-analysis of the data echoes what was found in two other re-analyses of 1960-70s era cholesterol/heart diet trials: Linoleic acid, with its high proportion of Omega-6 fatty acid and complete lack of Omega-3 fatty acid is really toxic stuff.
You can read the whole BMJ study here:
Use of dietary linoleic acid for secondary prevention of coronary heart disease and death: evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis.
Omega-6 Fatty Acids Promote Inflammation
The researchers believe that the reason that the polyunsaturated oils used in these cholesterol-lowering diets were so toxic was because the vegetable oils used were very high in Linoleic Acid, an Omega-6 fatty acid, and devoid of the countervailing Omega-3 fatty acids you need to consume to keep Omega-6 fatty acids from promoting inflammation.
So, okay. Safflower oil is now out of your diet. But it turns out that safflower oil is not the only common vegetable oil that is rich in linoleic oil. Corn oil is very high in it, too. You can see a complete list of oils sorted by their percentage of Linoleic acid HERE.
Finally, though health nuts who still fear that eating saturated fat will kill them will tell you that canola oil and flaxseed oil are healthier alternatives, neither of these oils has been a part of the human diet for any significant period of time the way animal and dairy fats have been.
Canola oil does contain Omega-3 fatty acids, but the process used to take away its rank smell and keep it from going rancid is likely to damage them. Damaged Omega-3 oils is not healthy. Flaxseed oil is the recently renamed stuff we used to call linseed oil and use for mixing up oil based paint--which it often tastes like. It's safe to eat if you keep it refrigerated and don't let it go rancid, but since it is not a traditional food, I would suggest eating it in small quantities.
Palm oil is another fat that has recently made its way into our food system, as manufacturers are using it as a replacement for the hydrogenated oils full of transfat. But while there may be health benefits from consuming the palm oil eaten in traditional societies, the industrially processed palm oil that is appearing on supermarket shelves is very different stuff and may very well be harboring transfat-like molecules that escape the FDA labeling requirements. And besides that, it often tastes--and refuses to melt--suspiciously like lipgloss. Treat it with caution.
Stick to the traditional healthy vegetable oils and fats like olive, coconut , and melted butter, and you are more likely to actually improve your health.