Fats in food are always a mix of different types of fatty acids -- when we say "saturated fat", we really mean the saturated fatty acids in the particular fat source. (See below for examples)
Although saturated fats are often thought of as a group, there are many different saturated fats, and each has different uses in the body and potentially different health effects. There is some evidence for positive effects of some saturated fats, including antibacterial properties. However, the various types of saturated fatty acids have not undergone a great deal of study.
Some saturated fats tend to raise both LDL and HDL cholesterol.
In the past few decades, saturated fat has been blamed for having a causative role in heart disease, but research has not shown this to be the case.
Sources:
Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients) (2005), Institute of Medicine, Food and Nutrition Board, National Academy of Sciences.
German, J Bruce, Dillard, Cora J. "Saturated fats: what dietary intake?." American Journal of Clinical Nutrition. 80/3 (2004).
USDA National Nutrient Database for Standard Reference, Release 20.
