I do not know how much truth exists in the theory that an excess of saturated fats is harmful, but I have acted based on this theory and it was very beneficial for me.

A few years ago, I have been diagnosed with incipient atherosclerosis. This was an unpleasant surprise for me, so I have immediately made serious changes in the food that I eat.

At that time, I was eating very high quantities of dairy, which has a high proportion of saturated fat.

Because I could not see any other factor that could cause the atherosclerosis, I have eliminated dairy from my food and I have changed completely the composition of the fats contained in my food.

I eat only food that I cook myself, so I know exactly which is the composition of the fat contained in it. Nowadays, at least 90% of my daily intake of fat comes from a combination of oils that I use when cooking food (typically 60 mL of extra virgin olive oil + 20 mL of cold-pressed sunflower oil + 10 mL of cod liver oil + 1 drop of an oil containing D3 and K2 vitamins).

Instead of any other kinds of dairy, now I use only a cheese substitute that looks and tastes like melted cheese, but it is made from whey protein concentrate (which has almost no fat) mixed with some vegetable oil and a few other ingredients for better flavor.

After changing completely the fatty acid profile of my fat consumption, after a year the symptoms of atherosclerosis have disappeared and there have been also other very noticeable signs of improved cardiovascular health. For instance, previously, I had cold feet and when sleeping I had to take care to keep them warm. Some months after changing the diet, they had become warm (presumably due to improved blood flow) and I have no longer needed any protection against lower temperatures.

So my diet change has very certainly improved a lot my health in a relatively short time of no more than a year, and that has persisted for the last three years. I cannot know if this is really caused by the change in the fatty acid profile, but I cannot see any other significant difference, except if the abundant dairy that I was eating before contained some other harmful substance or if the significant increase in the amount of eaten EV olive oil and cold-pressed sunflower oil has provided some benefits beyond the better fatty acid profile.

Logically, it is plausible that a reasonable amount of saturated fat, which is correlated with the amount of physical work, should not have any harmful effect.

As long as you burn enough calories daily to use all the fat intake for energy, it should not matter if that fat is saturated fat. However, when the fat is not completely used and some of it is deposited, then it is plausible that it is preferable if oleic acid (mono-unsaturated fatty acid) is the most abundant in food, because in normal conditions this is the most abundant fatty acid in the human reserve fat. When other fatty acids are much more abundant than oleic acid, they must be processed and converted before storage and the capacity for the conversion may be overwhelmed.

The negative connotations for "seed oils" are not applicable to all seed oils, but they refer only to the seed oils where linoleic acid is the most abundant acid.

Linoleic acid is an essential nutrient, but the need for it can be satisfied with 15 to 20 mL per day of a suitable seed oil, like sunflower oil. A greater daily intake than that can cause problems, because the excess linoleic acid must be converted into other fatty acids and also because some of its derivatives have physiological roles for which an excess quantity is not desirable.

Given these, it seems plausible that some fat composition is preferable to others. Like I said, I have acted on this assumption and it has worked very well for me, even if the real mechanism cannot be known, at least not yet.