Turning liquid oil into solid spread using chemicals and heat makes a really bad kind of fat called trans fat.

“During hydrogenation, the oil is heated to high temperatures and then hydrogen gas is forced through it using a metal catalyst. Typically, this catalyst is nickel. This process forcibly changes the molecular structure of the fat to make it solidify. But here's the problem. This process creates something called trans fats. Trans fats are widely considered to be the single worst type of fat someone can consume.”