Today, vegetable oils such as soybean, corn, safflower, sunflower, or cottonseed oil–or “polyunsaturated fats”–are commonly used to replace trans fats. But when heated to temperatures required for frying food, these highly unstable oils can create oxidation products that are extremely toxic. From The Big Fat Surprise: Why Butter, Meat & Cheese Belong in a Healthy Diet.
For more than sixty years, Americans have been told to eat polyunsaturated vegetable oils instead of saturated fats. This advice has been based on the simple reality that vegetable oils lower total cholesterol (and LDL cholesterol, too, as later discovered). The fact that vegetable oils also create toxic oxidation products when heated and trigger inflammatory effects linked to heart disease, are, it seems, less important to mainstream nutrition experts, whose focus hasn’t wavered from cholesterol. Most Americans don’t realize that their nutritional advice is based on such a narrow set of health concerns, nor that large edible-oil companies have been contributing funds to their trusted, guiding institutions, such as the AHA, as well as to schools of medicine and public health. And while the scientists at large food manufacturers might understand the problems of unsaturated oils, they have not had alternatives to work with, due to the prevailing stigma against saturated fats. Everyone has therefore gotten on board with the advice to use vegetable oils in both the home and industrial kitchens alike.
Our consumption has moved from saturated fats at the beginning of the twentieth century to partially hydrogenated oils to polyunsaturated oils. We have therefore unwittingly been subject to a chain of events starting with the elimination of animal fats and eventually winding up with aldehydes in our food. Looking ahead, it is little consolation that the FDA is poised to ban trans fats entirely, which will make liquid oils and their oxidation products even more common. Mom-and-pop restaurants, local cafeterias, and corner bakeries will then follow in the footsteps of the large fast-food restaurants in eliminating trans fats but will be less likely to employ rigorous oil-changing and ventilation standards into their operations. Despite the original good intentions behind getting rid of saturated fats, and the subsequent good intentions behind getting rid of trans fats, it seems that the reality, in terms of our health, has been that we’ve been repeatedly jumping from the frying pan into the fire.
The solution may be to return to stable, solid animal fats, like lard and butter, which don’t contain any mystery isomers or clog up cell membranes, as trans fats do, and don’t oxidize, as do liquid oils. Saturated fats, which also raise HDL-cholesterol, start to look like a rather good alternative from this perspective. If only saturated fats didn’t also raise LDL, the “bad” cholesterol, which remains the key piece of evidence against them. But like so many of the scientific “truths” that we believe but which, upon examination, start to crumble, maybe the LDL-raising effect isn’t quite an incontrovertible certainty, either.