Not all fats are created equal,Monounsaturated fats (MUFAs) lower total cholesterol and LDL cholesterol (the bad cholesterol) while increasing HDL cholesterol (the good cholesterol).Olive oil is a great source.
Saturated fats raise total blood cholesterol as well as LDL cholesterol (the bad cholesterol). Saturated fats are mainly found in animal products such as meat, dairy, eggs and seafood. Some plant foods are also high in saturated fats such as coconut oil.
Polyunsaturated fats also lower cholesterol and LDL cholesterol,seafood,corn,and sunflower oils are high in polyunsaturated fats.Omega 3 fatty acids belong with these guys.
Hydrogenated fat is created during food processing, fats may undergo a chemical process called hydrogenation. This is common in margarine and shortening. These fats also raise blood cholesterol. The saturated fat content of margarine's and spreads is printed on the package or Nutrition Facts label.
So, saturated fats is the bad guy it can increase your risk of heart disease by increasing your total and LDL ("bad") cholesterol. remember it's found in food derived from animal sources.
The best low-fat diet or maybe I should say best way of eating I have found are:foods in the Mediterranean diet pyramid.