So, what is fat, exactly? Fat as we know it in our food and in our blood is called a triglyceride. A triglyceride is made up of three fatty acid "tails" attached to a "backbone." A triglyceride can have three of the same fatty acid, or it can have a mixture of fatty acids.
A fatty acid starts with a chain of carbon atoms with hydrogen atoms and sticking out to the sides. If a fatty acid is saturated, then the chain is fully stocked ("saturated") with hydrogen atoms (two per carbon atom), which makes it form a straight line.
If a fatty acid is monounsaturated, then one carbon ("mono" = one) is missing a hydrogen atom, so the chain "kinks" at that point. In a polyunsaturated fatty acid more than one carbon ("poly" = multiple) is missing a hydrogen atom, so the chain kinks in more than one place.
A fatty acid is defined by how many carbons are in its chain and the number and location of it's "kinks," if any. Here's a representation of a saturated fatty acid (top) and an unsaturated fatty acid (bottom):
If a triglyceride is saturated, then all three "tails" lie straight and compact. That's why saturated fats like butter or the fat on beef or pork are solid at room temperature. If a triglyceride is monounsaturated or polyunsaturated, its tails are crooked and less compact, with space in between them, which makes the resulting fat fluid at room temperature (in other words, it's an oil).
So what should you be eating, ideally? Here's a brief rundown:
Saturated fats. Not all saturated fats are the same, because they come in different lengths. Some may be healthful, while others may increase your risk of developing high cholesterol and heart disease. There is a lot of controversy about this, and not all health and nutrition experts agree. It does look like the saturated fats in coconut oil may be beneficial for health. Research is ongoing, but I myself feel confident in using it. However, at this time I don't agree with the notion that coconut oil is some kind of "cure all" for whatever ails you.
Monounsaturated fats. Olive oil is the most notable of these heart-healthy fats. Macadamia nut oil and almond oil are also rich in monounsaturated fatty acids. Obviously, so are olives, macadamia nut oil and almonds! Monounsatured fats are an important part of the Mediterranean-style diets, which have been shown to reduce the risk of heart disease and some other serious health conditions (but don't start gulping olive oil for this reason...the Mediterranean diet is only as good as the sum of its parts).
Polyunsaturated fats. These include the omega-3s, found in fish, seafood and some other foods, including flaxseed. Omega-3 fatty acids are important for heart health in adults and cognitive development in fetuses and young children (and possibly in adults, too). Most of us need more omega-3s. The polys also include the omega-6 fatty acids, typically found in vegetable oils. These are generally healthful...unless we get way too many of them, skewing our omega-3 to omega-6 ratio. Omega-6s are found in abundance in processed foods, so many of us do get too many of them. Cutting back on processed foods and including a little more fish and flaxseed in your diet can help achieve a more healthful balance.
Trans fats. These are polyunsaturated oils that have been chemically altered to resemble saturated fats. These fats are so bad that some health experts have called them "metabolic poison." Many restaurants and food manufacturers are phasing them out due to consumer and legal pressures. Avoid any food that lists "hydrogenated" or "partially hydrogenated" oil on the ingredient label. [I'll be talking more about trans fats, and the fats that are now being used as "trans fat alternatives" in a guest post on a fellow nutrition student's blog in a few weeks. I'll link to it here when it runs.]
That's it in a nutshell. Tomorrow I'll talk a little about the current nutritional wisdom on how much fat we need in our diets and, perhaps more importantly, what we should be eating if we decide to reduce the fat in our diets.