In reality, it is not that simple. As Enig and Fallon (1998, 1999) point out in their article "The Oiling of America" the American diet before 1910 was largely based on animal fats like butter, eggs, lard and meats, and coronary heart disease and heart attacks were rare. Americans also wre less sedentary and often ate locally produced food during those years. There was no refrigerated, cross-country trucking of foods in those days.

The American diet began to change toward one that included more industrially produced options, such as margarines, factory baked goods and vegetable oils in place of lard. Even though research in the '50's and '60's pointed to the fact that were fewer instances of coronary heart disease prior to the dietary changes, American companies were promoting their cereals, corn oil and margarines as beneficial to health and good for lowering cholesterol. It was around that time that the American Heart Association began a campaign (based on research done on rabbits, which are vegetarian animals) to change America¡¯s diet to a "Prudent Diet"where butter was replaced by margarine, breakfast cereals replaced eggs and chicken and fish in place of beef. The familiar food pyramid was created and even taught in public schools.

None of the research supported that dietary model. In fact, there were many published research reports that indicated that the opposite was true. Enig and Fallow write that "in 1961 the AHA published its first dietary guidelines aimed at the public. The authors, Irving Page, Ancel Keys, Jeremiah Stamler and Frederick Stare, called for the substitution of polyunsaturates for saturated fat, even though Keys, Stare and Page had all previously noted in published papers that the increase in CHD was paralleled by increasing consumption of vegetable oils. In fact, in a 1956 paper, Keys had suggested that the increasing use of hydrogenated vegetable oils might be the underlying cause of the CHD epidemic."

Now, more and more research is indicating that Keys was right in 1956. Trans-fats (hydrogenated vegetable oils) are dangerous to health and still in wide use. While most animal fat sources are saturated, which just means they are made of straight chains of carbon and hydrogen that pack together easily and are relatively solid at room temperature, most vegetable sources are unsaturated. They are formed by more crooked chains of atoms and since they don't pack together easily are more likely to be liquid at room temperature (or even below that).

In order to take a vegetable source and make it into a butter-like substance, you have to modify its structure. This process is called "hydrogenation" and was discovered and patented by a French scientist. Later, Proctor and Gamble obtained the rights to that patented process for use in the United States. Crisco Oil.tm soon became the shortening of choice in American kitchens.

The problem with hydrogenation is that the process turns a healthy fat into a dangerous fat. According to Enig and Fallow¡¯s article, this process turns the vegetable-sourced unsaturated oils into straight "packable"molecules, by changing the placement of the hydrogen atoms at the location of their double bonds. In nature, most double bonds occur in the "cis"configuration, which means that both hydrogen atoms are on the same side of the carbon chain in the place on the chain where there is a double bond.