Ah, this response reminds me of the doctor who recommended a grapefruit and bacon diet to me (the Mayo Clinic Diet). I researched and realized that diet had been fully discounted over 20 years before!

The kind of fat your friends have been eating all their lives was probably processed, partially hydrogenated and/or mixed with sugars like high-fructose corn syrup and other processed carbs. This author did his research in a way that most doctors do not unless they are nutritionists. But if you don't believe me, talk to a nutritionist who is actually up-to-date on their knowlendge.