1. Dietary fats. The fat people are generally concerned about in their diet is found in a chemical structure called triglycerides. Triglycerides consist of a backbone molecule called glycerol that holds three fatty acids, thus the name triglycerides. Fatty acids are simply chains of carbon molecules with one acid end that attaches to the glycerol backbone and one stable methyl end. Most of the fatty acids in the diet are long chain (14 to 22 carbons), but some foods contain small amounts of short-chain (4 to 6 carbons) and medium-chain (8 to 12 carbons) fatty acids.

  2. Saturated fats. Saturated fats include those fatty acids that have all their carbon chains saturated with hydrogen atoms. This saturation makes them solid at room temperature.In general, animal fats provide approximately 40 to 60 percent of their fats as saturated fats and plants provide only 10 to 20 percent of their fats as saturated fats.

  3. Monounsaturated fats. Monounsaturated fats have one missing pair of hydrogen molecules. They are therefore unsaturated at one location and thus have one double bond. Monounsaturated fats are found in both animal and plant foods, but their richest sources are olive oil, canola oil, most nuts and peanuts, and avocado. A common monounsaturated fat found in the diet is oleic acid.

  4. Polyunsaturated fats. Polyunsaturated fats have two or more missing hydrogen pairs, and thus have two or more double bonds. These fats are further classified by the position of the first double bond from the stable methyl end as omega-6s and omega-3s.

  5. Omega-6 fatty acids. These polyunsaturated fatty acids have the first double bond positioned at carbon number 6. The most common omega-6 in the diet is the essential fatty acid linoleic acid, which is abundant in common plant foods: corn, sunflower,safflower, soybean, and cottonseed oils. Gamma-linolenic acid (found in evening primrose) is also an omega-6 fatty acid. Arachidonic acid is a longer-chain omega-6 found in animal products and is the form used to make the inflammatory eicosanoids. The body can convert linoleic acid to arachidonic acid.

  6. Omega-3 fats. These polyunsaturated fatty acids have the first double bond positioned at carbon number. The plant version, alpha-linolenic acid (ALA) is found in specific plant foods, such as flaxseed, flaxseed oil, hemp oil, canola oil, soybean oil, and English (not black) walnuts. The longer fatty-acid versions,eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are found mostly in fatty fish, which include salmon, sturgeon, striped bass, and anchovies and in fish oil capsules. A vegan version (Martek vegetarian DHA) derived from microalgae, however,has recently entered the market and may soon be added to selected food products.Obtaining omega-3s as DHA or EPA is thought to have some advantage as these versions are more biologically active. Alpha-linolenic acid has to be elongated in the body, which may be a slow or limited process, to more active DHA or EPA.

  7. Hydrogenated fats and trans fats. Hydrogenation is a process practiced by the food industry in which hydrogen atoms are forced onto vegetable oil molecules under high pressure and temperature. This converts unsaturated fatty acids into saturated ones, thereby converting a liquid oil into a soft solid with improved stability. Partial hydrogenation, in which only some of the oil’s unsaturated fatty acids become saturated,produces some unusual fatty acids that are called trans-fatty acids. Trans fat is found in vegetable shortenings, hard margarines, as well as crackers, cookies, snack foods,and many other foods made with or fried in partially hydrogenated oils. Margarines low in trans fat are now available.

  8. Medium-chain triglycerides (MCTs). Medium-chain triglycerides are saturated fatty acids with a chain of 8 to 12 carbons. Some can be found naturally in milk fat,coconut oil, and palm kernel oil. They are also made commercially as a by-product of margarine production. Medium-chain triglycerides are water soluble and are more easily and rapidly digested, absorbed, and oxidized for fuel than are long-chain triglycerides.MCTs are commonly recommended for people who have problems digesting long-chain fats. Research has not found that MCTs benefit athletes.