Regardless of whether you can believe it's not butter, you may wonder what margarine is exactly. It's creamy, yellow, and spreadable just like real butter, but there are major differences between the two products—the biggest being their ingredients.

Butter is a byproduct of milk, typically from cows. Churning the cream skimmed from milk creates a rich, semi-solid emulsion that can be used as a fat in baking and cooking or as a condiment. Though embraced by cuisines around the world, butter has become a topic of health debates. While it is a good source of calcium and vitamins, butter is also high in saturated fat, which has been shown to raise cholesterol.

Margarine is often marketed as a healthy alternative to butter, but that's not necessarily accurate. In general, the word margarine can describe any butter substitute. The first margarine was far from health food; French chemist Hippolyte Mège-Mouriès churned it from milk and beef tallow after Emperor Napoleon III offered a prize for a cheap butter replacement. A lot of margarine is vegan today, though some of it contains milk.

The main ingredients found in a typical tub of margarine are vegetable oil, water, salt, and emulsifiers. Legally, margarine must have a minimum fat content of 80 percent—the same percentage in dairy butter. Anything less would technically make it a spread. That means margarine isn't automatically lower in fat compared to butter, but the types of fat they contain may differ. Saturated fat is associated with animal protein, and it's more prevalent in butter. At one point, margarine was more likely to contain trans fats, which can occur in vegetable oils that are chemically altered to stay solid at room temperature. Such fats are linked to an increased risk of heart disease.

Artificial trans fats have been phased out by the FDA in recent years, so consuming them with margarine is no longer an issue. Still, health experts can't agree on which product is better to have on your toast. Butter may contain more harmful fats, but it's also rich in beneficial nutrients. And because the ingredients of margarine can vary so widely, it's hard to assign a healthy label to the whole category.

If you're lactose intolerant or don't eat animal products, vegan margarine may be a great replacement for butter in your diet. But if health is your main concern, make sure to check the information on the back of the box as well as the label on the front.

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