This is the most important dietary step we can take to protect ourselves from heart disease. Saturated fat raises LDL cholesterol, even more so than eating cholesterol-rich foods such as eggs and dairy products. Still saturated fat is not poison. And it can't be totally escaped it anyway. Even vegetable oils contain a little saturated fat.
Hydrogenation is a process used to harden vegetable oils to produce spreads like margarine.
The problem is that the procedure makes unsaturated fat chemically closer to saturated fat.