May 2 , 2005
by Laura Dolson
Not too long ago, fat was generally thought to be bad for you. They are a dense source of calories, for one thing. However, fats are needed in our bodies - all our cell membranes are mostly composed of fats, as are hormones and other "messenger molecules" in the body. Fats are also important for the absorption of certain nutrients, including phytonutrients. And, of course, they are our main "energy storage system", allowing us to go for periods without eating. Since fats are so vital, nutritionists have been trying to teach people about "good" and "bad" fats.
Essential Fatty Acids
In nutrition, when we say a component of our food is "essential", we mean a nutrient that the body can't make for itself. Vitamins, by definition, are essential. Certain minerals and amino acids (building blocks of protein) are essential. And there are certain fats which are essential. You may have heard of Omega-3 and Omega-6 fatty acids - the Omega-3's have been in the news a lot. These are the essential ones for us to get.
Omega-6 fatty acids are pretty easy to get. They are in a lot of the common oils we use in cooking, as well as nuts and seeds. Omega-3 fatty acids are much scarcer, and it is seeming that for good health we should seek out sources, as they protect against heart disease and other chronic illnesses. The main source in the human diet is in deep-water fish such as salmon, sardines, and tuna. Plant sources include flax seeds, walnuts, and soybeans.
Some research suggests that the ratio of Omega-3 to 6 in our diets is important - that not only do we need to add Omega-3, but that we may be getting too much Omega-6. But the research is still evolving on this - we will talk about this in class.
Omega-3 and -6 fatty acids are in a group called polyunsaturated fats. What the heck does this mean? Let's stop a minute and talk about "saturation" in fats, as it is a key concept.
The "Fat Train" - Picture a train, such as the one at Roaring Camp, and pretend that it's a long train of fatty acids.* The cars are the "backbone" of the fats (mostly carbon) and the people are hydrogen atoms. When the cars are full of people, we will call this "saturated" - no one else can sit down. If there is room in the car for a few more people, we will call this "polyunsaturated" ("poly"="many"), and if there is room for just one more, person we will call that "monounsaturated" ("mono"="one"). We will talk more in class about this, but one consequence of the type of fat is that "bad people" (in the case of fats, oxygen or some other random atom) might hitch a ride in one or more of the "spaces" on the train, causing it to "go bad" or rancid. Therefore, the higher the saturated fat content, the more shelf-stable the fat is.
Polyunsaturated Fats (such as corn oil and soybean oil) are the most apt to go rancid, especially when exposed to heat, oxygen, and materials like cast iron pans, which contain a lot of free radicals. So although polyunsaturated fats are needed in our bodies, they are also more prone to oxidation. There is some evidence that a diet too high in polyunsaturates may be a cancer risk, possibly for this reason (or maybe because of too much Omega-6). Again, the research is still "in progress" on this issue. This points out again my #1 Cardinal Rule of Nutrition: Eat a Variety of Foods in Each Category.
Monounsaturated Fats - These fats are more stable. They are sort of a "happy medium" between saturated fats, which have some bad effects in the body, and the polyunsaturates which oxidize easily. Monounsaturated oils have a positive effect on blood cholesterol and some other health measure. Olive oil is the classic oil that is mostly monounsaturates, and has the benefit of phytonutrients (antioxidants) as well. Cultures where people have traditionally consumed a lot of olive oil tend to have less heart disease. Other sources are avocados, almonds, hazelnuts, and the oils from safflower and sunflowers which are specially bred to be "high-oleic" (the regular oils from these plants is high in polyunsaturates.)
Saturated Fats - Saturated fats are thought to promote heart disease. However, it has recently pointed out that not all saturated fats are created equal, and in fact our bodies need saturated fats (although the human body can make all the saturated fat it requires). Recently, researchers have been studying them more and finding a more complex picture than was once thought. For example, people who consume a lot of coconut, which is high in saturated fat, don't seem to have the heart disease which is commonly associated with this fat. At this point, it's probably still wise to follow the guidelines of 10% of calories from saturated fat, but this advice may be modified in years to come. For the most part, saturated fats tend to be animal fats, such as butter.**
"Trans" Fats (hydrogenated fats) - These are the truly Evil Fats. These are polyunsaturated fats where the bonds have been artificially saturated with hydrogen. They are much worse than saturated fats in terms of promoting disease risk, in fact, it's possible that some of the problems attributed to saturated fats may actually be due to an increase in the use of partially hydrogenated oils. Shortening, most margarine, and most processed baked goods are sources of transfats, as is most microwave popcorn and many other processed foods. Read the labels!!!
Surprisingly, there is at least one naturally-occurring trans-fat, called CLA. It actually looks as though it's beneficial to us. It is mainly found in meats and poultry, especially if fed a diet natural to the species.**
Note that all fats are combinations of different fatty acids. Check out this link (look in the second chart, about half-way down the page):
NOTE: Please ask your parents about this! I am planning to demonstrate how homemade mayonnaise is made in class. This will be made with a raw egg yolk. I consider the risk of salmonella to be VERY low. Only one in 10,000 eggs is contaminated in the U.S., according to the Centers for Disease Control. I will use a very fresh egg yolk, and enough acid (vinegar and lemon juice) to further reduce the risk. However, I don't want any student to sample the mayo unless their parents agree. (Of course, no one has to - my feelings won't be hurt at all!)
*Thanks to Alton Brown and his TV show "Good Eats" for this analogy.
** The diet of the animal greatly influences the fat composition. We will talk about this in class. In general, animals that eat a diet rich in grains will have more saturated fat than grass-fed animals. Grass-fed beef has more Omega-3 fatty acids and CLA as well.