It is man made whereas butter is natural, and i am assuming that her father (quite rightly in those days) was wary of anything not natural. In hindsight though, margarines are polyunsaturated fats whereas butter is saturated fat - polyunsaturated fats, whilst still being fatty foods, are much better for you then the tube-clogging, heart-stopping, weight-gaining saturated fats which she has grown up on, and which is partly to blame for the UK being the heart-attack nation of the world. It pains me to say this as she is a nice lady but Clarissa D-W is a (barely) walking advert for switching from saturated fats to polyunsaturated fats as soon as possible (and a few trips to the gym also)