In this new century, news media are finally aware that America's major health problem is obesity. Excess weight not only contributes to almost every health risk, it can actually multiply the risk factors, including those from tobacco. It has already been reported that tobacco causes
more deaths than AIDS / HIV, maternal mortality, automobile accidents, homicide and suicide combined, yet obesity makes the risks even higher.
You don't have to be 300 pounds overweight for fat to be harmful. Being "pleasingly plump" or even leaner can be enough to increase your risks of various ailments, such as cancers, diabetes, heart disease, memory loss, menopause, osteoporosis, PMS, stroke.
Just substituting margarine for butter is not enough, especially if the spread is made with hydrogenated oils or "trans fatty acids".
Good fats, the "essential fatty acids" that the body can not make, can be found in fish, nuts, soy and other foods. For most fats, if you have none in your diet, your body will make what it needs.