There are three main types of fat in food: saturated, monounsaturated, and polyunsaturated. Other types of fat are cholesterol and fats formed during processing of unsaturated oils (hydrogenated fat and trans-fat).
The saturated form of fat is usually solid at room temperature. Key food sources are animal fats such as butter, lard, milk, cheese, cream, and the fat in meat and poultry. Tropical oils like palm and coconut oils also contain large amounts of saturated fat. Saturated fat is most closely associated with increased health risks. This fat has been shown to increase “bad” cholesterol levels (LDL cholesterol) and decrease “good” cholesterol levels (HDL cholesterol). For this reason, our saturated fat intake should be limited to no more than 10% of calories. In older adults, this would be about 20 g/day for women and 25 g/day for men.
Monounsaturated fats appear to lower “bad” cholesterol levels in our blood while increasing “good” cholesterol. Olive oil is one of the richest sources of monounsaturated fat. Other food sources are canola or peanut oil; margarines made from olive, canola, or peanut oil; and nuts and seeds.
Like monounsaturated fats, polyunsaturated fats lower total cholesterol levels in our blood, especially when used as a replacement for saturated fats. These fats are usually found in oils that are liquid at room temperature such as safflower, sunflower, corn, and other vegetable oils. Other food sources include margarines made from these oils, nuts, seeds, and fatty fish such as salmon, trout, mackerel, sardines, and tuna. Fish oil fats are also known as omega-3 fats. In contrast to other polyunsaturated fats, they do not lower blood cholesterol. However, they do seem to lower blood triglycerides, another type of blood fat associated with increased risk of heart disease.
Cholesterol occurs naturally in animals and is an essential part of life. About 80% of cholesterol is made by our liver while the other 20% comes from our diet. The cholesterol that comes from the diet is low-density lipoprotein (LDL) cholesterol. This is known as the “bad” cholesterol because it contributes to the formation of sticky plaques in our arteries. Due to these plaques, blood flow is reduced and can lead to heart attacks or strokes (brain attacks). Scientific studies have shown that our blood cholesterol levels are more affected by the amount of saturated fat rather than cholesterol that we eat. High-density lipoprotein (HDL) cholesterol is known as the “good” cholesterol because it can reverse the build up of plaque in our arteries. This cholesterol does not come directly from food but is produced in our body and can be increased through exercise and by increased consumption of vegetables and fruit. Cholesterol is found in all animal products such as meat, poultry, eggs, milk, and cheese. Plant food sources do not contain cholesterol. For example, cholesterol-free potato chips or cholesterol-free vegetable oil never contained cholesterol in the first place.
Other types of fat are found in human-made products. Hydrogenated or partially hydrogenated fats are originally from unsaturated (monounsaturated or polyunsaturated) fats. The process of hydrogenation turns unsaturated fat into something more like a saturated fat. Some examples of hydrogenated fat are shortening and some margarines. Non-hydrogenated margarines are made by a process that involves the addition of small amounts of saturated fat to vegetable oil. Trans-fat is produced during the hydrogenation process. Trans-fat acts like saturated fat by increasing “bad” cholesterol and potentially decreasing “good” cholesterol. Sources of trans-fat include processed foods such as hydrogenated margarines, some cheeses, and prepared baked foods such as cookies, pies, and crackers. Trans-fat is not listed on food labels but can be identified on ingredient lists as “partially hydrogenated” vegetable oil.