Margarine was originally manufactured to fatten turkeys but it killed them instead. What do to? It was colored yellow and sold as a butter substitute.
While both have the same amount of calories, butter has eight grams of saturated fat while margarine has five. However margarine is hydrogenated and full of trans-fatty acids so it increases the risk of heart disease and cancer, affects breast milk, weakens the immune system and depresses insulin response.
Butter is natural and good for you: it increases the absorption of many vital nutrients, tastes good (especially when used for cooking) and has been used traditionally for centuries in cultures that had no heart disease, cancer, diabetes or obesity.
Margarine is synthetic, only one molecule away from being plastic and shares 27 ingredients with paint. Leave margarine outside and no flies will go near it; it doesn't go bad and nothing grows on it because it has no nutritional value.