All humans need fats to live, but there are good fats and bad fats.
Saturated fat is a BAD fat. It comes mainly from animal products, and raises total blood cholesterol levels and low-density lipoprotein (LDL) cholesterol levels, which can in turn increase the risk of heart disease and type 2 diabetes.
Trans fat is a BAD fat, and comes mostly from addition to processed foods to add texture and improve keeping abilities. Trans fat raises LDL levels and can decrease levels of the “good” cholesterol called HDL.
Monounsaturated and polyunsaturated fats are GOOD fats. They reduce blood cholesterol levels, protecting against various forms of heart disease and diabetes.