By Dr. Beth Gruber, CarbSmart Contributor
Posted 2/23/2002
Today we are starting our discussion of fats and oils as foods. In this article, we will explore the definitions of the words fats and oils, and we will talk about the characteristics of these substances.
A Definition Of Terms
To make sure we are always on the same page, we have to make a differentiation between the words 'fat,' 'dietary fat,' and 'body fat.'
- I will use the phrase dietary fat whenever I am referring to fats that we eat.
- I will use the phrase body fat whenever I mean the fat stored in our tissues, on our hips, or elsewhere in the body, including both the normal amounts and the excess.
- And I will use the word fats, without any other descriptive word, when talking about the substances themselves.
The Composition Of Fats And Oils
Fats and oils are one of the three kinds of substances known as lipids. In addition to fats, lipids include the compounds known as phospholipids (FOS-fo-lip-ids), and those known as steroids. We will talk about phospholipids and steroids as we go along, but for now, we are focusing
on fats.
Fats, like carbohydrates, are composed of the same basic elements: carbon, hydrogen, and oxygen. However, the smallest units of fats (called molecules of fat) are larger than molecules of carbohydrates, and the relative proportions of carbon, hydrogen, and oxygen to each other in fats is different from those in carbohydrates.
One molecule of fat is formed by the union of one unit of a substance called glycerol, with three units of substances called fatty acids. There are a great many different types of fatty acids, but the dietary fats found in our foods and in our body fat are, for the most part, formed from only three kinds of fatty acids. (For those who are
keeping notes, these are known as oleic acid, palmitic acid, and stearic acid, and they form fats known as olein, palmitin, and stearin.)
Glycerol (GLIS-er-all), sometimes called glycerin or glycerine, has three "arms." Each of the three arms joins with one fatty acid to make a single molecule of fat. This explains why fats are referred to as tri-glycerides (usually spelled triglycerides, without the hyphen). These are the simplest fats.
The Composition Of Fats And Oils
Dietary fats are mixtures of the three fats mentioned above, olein, palmitin, and stearin. Differing amounts of each of the three result in the different characteristics of each type of dietary fat. For example, more olein and less of the other two lowers the melting point of the fat. When a fat has such a low melting point that it is liquid at room temperature, it is called an oil. Among these are olive oil, canola oil, and cod liver oil.
Human body fat contains from 70 to 80 percent olein, and therefore has a melting point below normal body temperature. As a result, simple body fats are found in the form of droplets of oil in body cells. In addition, nearly all body cells contain at least some body fat.
Pure fats are odorless and tasteless. The smell that we associate with fats, especially when cooking them, is due to foreign materials that have been absorbed into the fat. The smell of bacon cooking is due to the pork, not the fat. Rancid or spoiled fats smell bad because of bacteria action acting on the fats.
Fats are not soluble in either hot or cold water. Fats that are hard at room temperature can be melted, but they still don't mix with water any more than oils do. You can shake oil and vinegar together in a jar, but as soon as you stop shaking, the water-soluble vinegar separates from the oil.
In order for fats and oils to be able to be mixed with water, they must undergo a process known as emulsification (E-mull-se-fa-KAY-shun). Emulsification is a process by which each droplet of fat is surrounded by a droplet of the emulsification agent. This holds the fat in solution long enough for it to be used.
The reason we can wash our dishes in water is that we use soap, which is an emulsifier. Soap holds the grease (the fats and oils) long enough for them to be washed away. We will talk more about emulsification when we talk about fat digestion.
The Difference Between Saturated And Unsaturated Fats
In large part because of the great Fat Versus Low Fat controversy that has been going on for half a century, many people tend to think that the only thing anyone needs to know about fats is whether they are saturated or unsaturated. The essential difference between saturated fats and unsaturated fats is that the one is hard at room temperature, and the other is liquid at room temperature.
The word 'saturated' means 'filled to capacity.' When talking about saturated and unsaturated fats, we are really talking about the amount of hydrogen in the chemical make up of the particular fat, compared with how much hydrogen that fat is capable of holding.
- Unsaturated fats have fatty acids with less hydrogen than they can hold. These fats are liquids at room temperature, and are called oils.
- Saturated fats have fatty acids that are holding all the hydrogen possible, and they are hard at room temperature, like butter.
Once a fat is fully saturated, it cannot be made unsaturated, but an unsaturated fat can be converted to a saturated fat. This is done by heat, or by other chemical means, in a process known as hydrogenation (high-DROG-gen-nation).
What Are Partially Hydrogenated Oils?
The familiar phrase 'partially hydrogenated oil,' which appears on a great many labels, particularly fast food labels, means that the unsaturated liquid oil was partially converted to a more solid fat. This is done to make the food item more substantial.
New studies appear to indicate that the partial-hydrogenation process is not good for health because it produces changes in the chemical structure of the fats that are unsafe.
Until Next Time...
In my next article, I will continue with our discussion of fats. We'll look at the functions fats play in the body, and then begin talking about fat digestion.
Join me, won't you?
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