[marvin]

I am once again super confused. During my whole primary education, highly poly-unsaturated fats were considered beneficial with regards to cardiovascular health. Saturated fats and trans fats were considered the culprit.

What changed, and when?

[samatman]

During my whole primary education, trans fats were considered a healthy alternative to saturated fat, this was universally promoted by the same authorities, and tens of millions of people suffered poor health, obesity, and premature death.

Unlike tobacco, none of the researchers responsible for this calamity have been censured, sued, or otherwise suffered negative consequences. They are, for the most part, still in power, and research is conducted under their auspices.

Does this mean they're wrong about linoleic acid being healthy as well? No, not inherently, but it does mean that it's worth looking elsewhere and drawing your own conclusions.

[adrian_b]

Linoleic acid is an essential nutrient for humans, who must obtain it from their food.

However, all nutrients, including all essential nutrients, have a range of daily intakes within which they are healthy, and when eaten in much greater quantities than the upper limit of that range they become unhealthy, or even dangerous.

For example a too low selenium daily intake can cause illnesses, but eating selenium only a few times more than the maximum recommended intake can cause a severe poisoning.

That is true also for linoleic acid, in moderate quantities it is very healthy, in too large quantities it is unhealthy.

Until the last few centuries, it was extremely unlikely for anyone to be able to eat too much linoleic acid. It was possible to do that if one would have eaten huge quantities of, for example, pine nuts, poppy seed paste or walnuts, but all those were quite expensive so most people would not have been able to buy enough of them, much less eat enough of them, to suffer from that.

That changed especially since the 19th century, when the industrial production of edible oils began to provide large quantities of cheap vegetable oils, like sunflower oil and many others, which have a very high content of linoleic acid.

These cheaper oils have replaced the traditional olive oil and also the animal fats in most applications, which resulted in a greatly increased consumption of linoleic acid.

So for most people, now it is more likely that they might eat too much linoleic acid, than it is that they might eat too little linoleic acid.

[Jensson]

Poly unsaturated fats easily becomes trans-fats when heated. This is very common in factory produced food since trans fats melt at higher temperatures making their shape easier to keep if you turn the poly unsaturated fats to trans fats.

But I don't think there are any dangers to poly unsaturated fats other than them easily turning into trans fats, so as long as factories are banned from making them into trans fats it should be fine. Or really the opposite, poly unsaturated fats are the healthiest fats, omega 3 and omega 6 and so on belongs to this group, just be sure to treat it carefully and don't let it turn to trans fats.

[bluGill]

There is one other problem with poly-unsaturated fats: they spoil fast - a few months at best at room temperatures. Since the crops are often harvested yearly and it takes time to get from field to market to your cupboard this is a real problem.

[feet]

Sounds to me like if you avoid heating them it's fine, which means there should be no issue with dietary PUFAs.

[Jensson]

Yeah, canola oil should be fine to use if you add it to food yourself. But as ingredients in fastfood or bread or chips it is likely they heated it enough to create trans fats.

[feet]

So the heating thing appears to be false. I wasn't able to locate literature in my brief search on the subject so perhaps someone can post a link

[ZeroGravitas]

Nothing changed:

Here's the British Heart Foundation:

> Contrary to some of the reporting on this issue, cutting saturated fat doesn’t necessarily mean lowering all fat. We all need some fats in our diet and, over time, the very low fat diets recommended in the past have been put to one side as our understanding of the effect of this nutrient has developed. So, current guidance tells us to switch from saturated to unsaturated fats rather than cutting the fat completely.

> However, it is still important to talk about processed foods and what is in them. A lot of the food we eat is pre-prepared, and while sometimes the processing is as simple as canning tomatoes, processed foods also include foods like ready meals, sweet treats or processed meats where food manufacturers can alter the amounts of different fats, salt or sugar.

> As with our diets, when one thing goes out, something else will take its place. The concern is what saturated fat is replaced with when it is removed. Replacing saturated fat with refined carbohydrates, like sugary foods, or trans fats won’t improve our health, but replacing them with unsaturated fats seems to have a positive benefit.

> We also know that we are already eating too much salt and sugar on average so, while we welcome changes to reduce saturated fat in our everyday products, we also want manufacturers to be mindful of what they replace it with. As consumers, we still need to keep an eye on food labels to understand what is in the foods we are buying and make the best choices for ourselves, too.

[bluGill]

In my youth it was assumed that the problem with fats is when they were solid at room temperature. Thus saturated fat was assumed to have the same effect as much cheaper trans fat, so they studied trans fat and called saturated fat bad. Then someone else recommended margarine (transfat) over butter because the headline said saturated fat (and the article may not have even mentioned they actually tested trans fat because there was thought to be no difference)

Some of this was science not knowing they needed to check things, but a lot of it was media and industry groups trying to sell a product and running a with half truths that fit their narrative. there are a lot of old studies that we cannot/should not reference today at all because things we now know are important were not something science took care to control for.

Problem is good science takes years. Health authorities need to make recommendations today, and often for political reasons don't get the option to say I don't know.