I never really understood this debate because, to me, I would just assume butter was healthier as it is from a whole food source (and tastes a whole lot better). It wasn’t until I started getting into nutrition that I really discovered margarine and read all about how “unhealthy” butter was.
The argument is that butter is full of saturated fats (which it is) and raises cholesterol and margarine was created as a healthy alternative, full of polyunsaturated vegetable oils.
Butter is basically just milk fat that has been separated from the liquids. As you’re probably well aware, dairy products are high in saturated fat. You’re also probably well aware that the consumption of saturated fat is one of the most debated things in nutritional science. The claim is that saturated fat raises LDL cholesterol (bad cholesterol) and increases your risk of developing heart disease. What people don’t often know is that although saturated fat raises LDL cholesterol, it also increases the HDL cholesterol (good cholesterol) so it really doesn’t harm your cholesterol levels. Scientific studies suggest there is no link between saturated fat and heart disease.
Margarine was created to replace butter in the diet. It is generally made from vegetable oils which are liquid at room temperature. To fix this problem, they hydrogenated the oil, basically, that just means they exposed the oils to high pressure and heat and hydrogen gas, this changes some of the unsaturated fat to saturated fat, so it remains solid at room temperature. This then creates a side product, trans fat. Which is not what you want in a healthy diet. There is a new process called interesterification which does the same thing minus the trans fats but is still highly processed. On top of that margarine has added colours to make it yellow (it actually starts off black) and emulsifiers, making it not so healthy and natural.
Personally, I believe that eating whole, real food such as full-fat dairy is better for you than eating processed margarine. Eating real food without any added nasties is my philosophy when it comes to food and I hope you can adopt that philosophy too.