Shedding fat and staying fit: problem with polyunsaturates
"Cholesterol-free!" polyunsaturated vegetable oils (like safflower oil) were promoted widely in the 1970s and were embraced with equal enthusiasm by millions of Americans because they lower blood levels of cholesterol. But it's important to recognize that these oils are far from a cure-all, because their cholesterol-lowering advantage is offset by known and suspected hazards.
Growing scientific evidence has linked the consumption of dietary fats, including polyunsaturated fats, to the development of obesity, a well-established risk factor for heart disease. So it certainly seems unwise to recommend diets high in polyunsaturated fats as a means of reducing cholesterol. In addition, diets high in fat of any kind (except perhaps fish oils) have been closely linked to the development of cancer - particularly breast, colon, and prostate cancer. Moreover, polyunsaturated fats are associated with gallstone formation.
There has been much speculation about the chemical instability of polyunsaturated oils, which react readily with other elements, particularly oxygen, to form damaging "free radicals" and thus may render cells and tissues more susceptible to premature aging and the development of cancer. These known and suspected risks, as well as the observation that there are no human populations who have a good health record while consuming a diet high in polyunsaturated vegetable oils, are why the American Heart Association has recommended limiting the consumption of polyunsaturated oils in its overall recommendation to reduce the intake of all fats.
So by all means don't be swayed by commercials that urge you to cut cholesterol by eating more margarine or vegetable oils, just because they are cholesterol-free or because of their high poly-unsaturated-fat content. Both are highly processed, nutrient-poor foods that add little to your diet nutritionally.
It's important to understand that because many margarines contain partially hydrogenated vegetable oils, they actually have more saturated fat than the original oil as a result of the hydrogenation process. And, although non-hydrogenated vegetable oils don't promote cholesterol production the way saturated fats do, remember that margarines, because they are partially hydrogenated, may have a reduced tendency to lower cholesterol. Moreover, both margarines and oils are among the most highly refined and calorically concentrated foods you can eat: It takes almost fourteen ears of corn to produce just one tablespoon of corn oil! (And if you added that tablespoon of oil to a big bowl of fresh salad, brimming with vitamins, minerals, and fiber, you wouldn't add many nutrients to it - but you'd quickly double, or maybe even triple, the calories in it!)