Margarine is vegetable oil that has been hydrogenated so it stays solid at room temperature. This gives it a lower smoke point and means it doesn’t have to be refrigerated, which makes it cheaper and more accessible, but it’s not Paleo.
Paleo and PUFAs
Hydrogenated vegetable oils are full of polyunsaturated fat (PUFAs), which we try to limit in our Paleo diets because they’re inflammatory and extremely unstable. They tend to oxidize when exposed to heat and light, making them very dangerous to cook with because consuming oxidized fat is much more likely to result in oxidized cholesterol in the blood. Cholesterol is not inherently bad, but it’s the oxidized cholesterol that’s more likely to latch onto the insides of our arteries and cause problems.
Paleo and Trans Fats
Hydrogenated vegetable oils also come loaded with artificial trans fats. By injecting hydrogen atoms into the oil, the process eliminates the double carbon bonds of the oil, thereby “saturating” the fat.
Although we normally promote consuming plenty of saturated fat as part of a Paleo lifestyle, hydrogenated vegetable oils are nothing like the healthy fats we get from butter and coconut oil. By interfering with the carbon bonds, the fat is rendered unrecognizable to our bodies: they don’t know what to do with it. The result is often a rise in insulin resistance, belly fat, and inflammation (source).