Lipids & Nutrition |
Fats & Oils
Fats and oils are lipids that are used by various organisms as a way of storing energy. (This is why you gain weight when you eat more than you need -- your body stores the extra calories as fat). When it comes to food, one gram of fat or oil has 2.25 times more calories than the same amount of carbohydrate or protein.
Fats: Highly saturated and generally solid at room temperature. Most often found in animal products, since animals tend to store energy in the form of fat. Animal fats used in foods include lard (pig fat) and butter (which is mostly fat).
Oils: Less saturated than fats and usually liquid at room temperature. Most often found in plant products, since plants tend to store energy in the form of oil. Plant oils used for cooking include corn oil, canola oil, and peanut oil.
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Melting Points
The melting point of a substance is the temperature at which it changes from a solid to a liquid. Substances with low melting points (like oils) don't require much warming to stay liquid (and many oils will stay liquid even in the freezer). Substances with higher melting points (like lard) must be heated up before they will liquify. |
Saturation
One carbon atom can bind to as many as four other atoms. Lipid molecules often have one or more hydrocarbon chains connected to the main molecule. Saturation describes how many of the carbons in those chains are bound to hydrogen atoms versus how many are double bonded to other carbons. The more saturated a lipid is, the higher its melting point will be, and the less healthy it will be for you to eat. Diets high in saturated fats are associated with the development of clogged arteries and heart disease. |
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In a saturated hydrocarbon chain (left), the most bonds possible go to hydrogen atoms. In unsaturated chains (right), bonds that could have been used by a hydrogen go a carbon instead. Notice that the double bond makes a kink in the chain. Monounsaturated = one double bond in a chain, while polyunsaturated = more than one double bond in a chain. You'll see these terms on food labels because the less saturated a lipid is, the healthier it is to eat. Many vegetable oils are polyunsaturated.
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Saturated |
Unsaturated |
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You can imagine that lipid molecules with long, straight hydrocarbon tails are easy to pack tightly together. Indeed, the more saturated a lipid is, the higher its melting point is. |
You can imagine that lipids molecules with curly hydrocarbon tails are hard to pack tightly together. Unsaturated lipids (like oils) have very low melting points. |
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We can artificially saturate oils through the process of hydrogenation, where unsaturated carbons have extra hydrogens forced onto them. Why would we do this? Remember that more saturated = higher melting point = more solid at room temperature. Hydrogenation is used to make solid margarine from liquid vegetable oils. |
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