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If you chemically saturate an unsaturated oil with hydrogen atoms, you now have a heat- and light-stable oil with a high burning point. This is exactly how commercial vegetable oils are produced for longer shelf lives and better utility. The process changes its chemical configuration to trans, though -- which is quite deleterious to health.
Trans fats raise bad cholesterol (LDL) and lower the good (HDL); furthermore, they do direct damage to cell walls, weakening the insides of arteries and causing cardiovascular disease. You find these commercially treated oils in processed foods like doughnuts, breads, pies, French fries, margarine and salad oils.
So what about saturated animal fat, some of which occurs naturally in trans configuration? Research shows that if you're at a normal weight, animal fats of any configuration are not damaging to health. Based on all recent findings, I recommend using good unsaturated oils such as olive as your basic food oil.