Common food sources. Butter, coconut oil, breast milk, and meat all contain mostly saturated fats. Avocados, nuts, and olive oil all contain a predominance of unsaturated fats.
Animal foods vs. plant foods. Saturated fats mostly come from animal foods. Unsaturated fats mostly come from plant foods.
Solid vs. liquid form. Saturated fats are mostly solid at room temperature. Unsaturated fats are mostly liquids at room temperature.
Storage. Saturated fats store well at room temperature. Unsaturated fats spoil quickly at room temperature.
Recommended consumption. The most generous guidelines suggest consuming no more than 10 per cent of calories from saturated fat. The most generous guidelines suggest consuming no more than 30 per of calories from unsaturated fat.
Effects on cholesterol. Saturated fats lower HDL (good) cholesterol and raise LDL (bad) cholesterol. Unsaturated fats lower LDL (bad) cholesterol and raise HDL (good) cholesterol.
Chemical structure. Both saturated and unsaturated fats are made of chains of carbon atoms. Saturated fats don't have any double bonds between the carbon atoms. Unsaturated fats have at least one double bond between carbon atoms.
Now for the painless chemistry lesson. Take a look at the chemical diagrams of fatty acids shown below.
Palmitic acid, which is found in palm oil, and stearic acid, which is found in meat, don't have any double bonds between carbon atoms. They are saturated. Oleic acid, found in olive oil, and linoleic acid, found in corn oil, have double bonds between carbon atoms. They are unsaturated.
The significance of the double bonds is that they make it easy for molecules to "slide" over each other, keeping the substance liquid at lower temperatures. And the double bonds are more vulnerable to reaction with oxygen, causing the fat to spoil. But what spoils on your kitchen table does not spoil inside you!