The diet of human beings consisted of a higher ratio of saturated fat vs. polyunsaturated fat until recently. Vegetable oils (polyunsaturated fat) became widely available on a daily basis only about 50 years ago. In the same time, the consumption of butter (saturated fat) declined. This means that over the past decades the composition of the fat in our diet changed from high saturated fat to high polyunsaturated fat.
Our brain is composed of 70% fat, mostly in the form of myelin that insulates nerve cells. Fat is also the primary component of cell membranes in our body. Any change in the composition in our diet can have profound physiological effects on our health.
"Changing the proportion of saturated to unsaturated fats in the diet, [...] might well change the composition of the fats in the cell membranes. This could alter the permeability of cell membranes, which determines how easily they transport, among other things, blood sugar, proteins, hormones, bacteria, viruses, and tumor-causing agents into and out of the cell. The relative saturation of these membrane fats could affect the ageing and the likelihood that blood cells will clot in vessels and cause heart attacks."In the 1950s, a trial (Anti-Coronary Club Trial) had been conducted to see the benefits of a "prudent diet" which consisted of a high ratio of polyunsaturated fats (corn oil and margarine). The polyunsaturated fat ratio was 4 times greater than that of typical American diets. The control group consumed a typical American diet. Results: 8 members of the group died of heart attacks, nobody in the control group.
- Gary Taubes
In 1969, Seymour Dayton reported the following of his trial where again in one group the saturated fat from butter, milk, cheese, ice cream, had been replaced with corn, soybean, safflower and cottonseed oils. The members of the other group were eating a diet higher in saturated fat from animal products. The death rate was equal in the two groups. The cholesterol level dropped in the first group, however the cancer rate was higher than in the saturated fat group. This vegetable oil diet failed to increase longevity. (Polyunsaturated fats also cause cancer in laboratory animals.)
The Helsinki Study: The same type of experiment as above: one group was given a high vegetable fat diet, the other a normal saturated fat diet. The men in the vegetable fat diet lived longer, but the women did not.
After the Minnesota trial (1968), where two groups of people were given a similar diet as described in the trials above, had similar results with the Helsinki Study: women had more heart attacks than the saturated fat group.
Overall, these vegetable fat diets were associated with an increased risk of heart disease.