I believe it coincided with converting to a nearly sedentary culture. Nothing is as bad for you as being sedentary and since many/most people refuse to exercise, and you can't buy exercise pills (let alone get people to take them), you have to get people to want to cut down on the stuff their body isn't using.

Cholesterol isn't bad, saturated fat isn't bad, but if you're sitting around all day festering so are they.

Nutrition is far from an exact science and humans from around the world react to foods differently in subtle ways giving any Nutritional conclusions limited relevance.

IMHO, The 2 most important things you can do are exercise and pay attention to your body. Also, a lot of these "mis-conceptions" come from media and laymen thinking that phrases like "a link between saturated fat and heart disease" imply causation.

Remembered one more thing: A lot of shit food is loaded with saturated fat and cholesterol (and salt and sugar). Frozen dinners, snack cakes and fast food are some great examples. These products, which significantly contribute to the fattening of the world, help give their main flavor sources a bad name.