G’day
Back in the '70s there was a study that found that people who eat olive oil in quantity (such as the populations of southern Italy and southern France) suffer markedly less hardening of the arteries than people who eat similar diets with butter in place of the olive oil (such as the populations of northern Italy and northern France). Butter contains only saturated fats, and olive oil contains mono-unsaturated fats. People guessed that this was the reason, and further leaped to the conclusion that if mono-unsaturated fat is good, polyunsaturated must be better. That is the extent of the evidence that margarine is healthy.
It has since turned out tha the real reason that olive oil suppresses arterial disease is that it contains the essential fatty acid lineoleic acid (7%). Most dieticians have paid no attention. Some other vegetable oils contain even higher proportions (safflower oil 79%, sunflower oil 69%, sesame 41%, peanut 29%). But others contain alpha-linoleic acid, which promotes arterial disease, hypertension, and type II diabetes. These include flaxseed (57% alpha-LA), canola (10%), walnut (7%), and corn oil (2%). On this basis, it would seem that margarines made out of some oils might be good for your arteries, and margarines made out of others (eg. flaxseed oil, canola oil) might be very bad for them.
Now, margarine is generally made out of plant oils by a chemical reaction that transforms their fatty acids from cis- configurations that are liquid at room temperature to isomers with a trans- configuration that are solid at room temperatures. No natural food contains trans- fatty acids, and we are not adapted by evolution, nor intended by God, to eat them. Recent studies show that trans- fatty acids in the diet cause a significantly elevated rate of several cancers. On these grounds you ought to avoid margarine like poison.
As for butter, it turns out that the elevated rates of heart disease in the French and Italians with the butter diets are caused not by anything in the butter, but by its comparative lack of linoleic acid. If you eat plenty of olive oil on your salad, there is nothing wrong with putting butter on your bread. Moreover, butter consists of saturated fats that cannot undergo any cis- to trans- transformations when heated. So if you are frying or sauteeing, it is safest to use either a vegetable oil with a very high smoke point (eg. olive oil) or a saturated fat such as butter, lard, or dripping.
Now, the process of arteriosclerosis involves cholesterol being laid down in the arteries, and one of the first statistical correlations noted was with high levels of cholesterol in the blood. It seemed, therefore, sensible to reduce cholesterol in the diet. And butter contains cholesterol. This has for twenty years been the chief argument that makes out butter to be unhealthy.
Fortunately, this argument is biochemical nonsense. 80% or more of the cholesterol in human blood is made in the liver, not absorbed from food. If you cut down on cholesterol in your diet, and unless you starve yourself, your liver will simply restore the original level by making more. Moreover, it turns out that cholesterol levels are only a poor indicator of risk for heart disease. Specialist ignore them, and concentrate on the ratio of low-density to high-density lipoproteins.
On balance, there is no reason to believe that butter is unhealthy, unless it is consumed to the exclusion of oils containing linoleic acid. And margarine is at least somewhat carcinogenic (as is the solidified vegetable fat used in frying most fast food).
Regards,
Agback