|Last update November 11, 2021, article reviewed & updated multiple times since March 9, 2002.|
What You Need to Know
What We Have Already Learned
In the last article, we began our discussion about fats and oils as foods. We started by talking about just what are dietary fat, oils, and related substances. We also made the important differentiation between fats (the substances themselves), dietary fat, and body fat (which is both the structural fat and the adipose tissue).
We learned that fats and oils are some of the compounds known as lipids, and are chemical combinations of a substance called glycerol with three of a number of different substances called fatty acids. Different arrangements of the fatty acids produces different kinds of simple fats, and simple fats join together in the construction of more complex lipid structures, such as cholesterol. Complex lipids break down into simpler fats.
Fats can join with phosphorus compounds to make phospholipids such as lecithin, and fats can also form loose combinations with certain proteins to make important compounds called lipoproteins. Lipoproteins are crucial because they are soluble in water, while fats are not. This water solubility means they can pass into and out of body cells more easily.
We learned that the difference between fats and oils is that oils are liquid at room temperature while fats are solid, and we saw that the difference between saturated and unsaturated fats has to do with the amount of hydrogen in the fat structure. Now we are ready to talk about the various functions of fats.
Functions Of Dietary Fat: The Caloric Value Of Fat
Fats have had so much “bad press” that many people forget that they are absolutely needed for life. Among the many functions of fats in the body is that they provide a lot of energy in the form of calories. To understand this, we need a short detour here to talk about calories.
Calories are a measure of the heat produced by the utilization of foods in the body. Carbohydrates and proteins produce four Calories. (***See the note at the end of the article.) of heat per gram. Carbohydrates, proteins, and fats are all composed of hydrogen, oxygen, and carbon, but fats don’t have enough oxygen built into their structures to allow for breakdown. Oxygen has to be added into the mix from the oxygen in the blood.
This process is called oxidation (ox-e-DAY-shun), and it gives rise to a great deal more caloric heat than is involved in the breakdown of carbohydrates or proteins, which do have sufficient oxygen. The heat value of a pound of fat is equal to the heat value of two and 1/4 pounds of carbohydrate or protein. This is why we say that fat has 9 Calories per gram while carbohydrates have only 4 Calories.
Body Fat As Storage of EnergyBody fat provides the most important reservoir of stored energy as adipose tissue. Even in a person who is not overweight, body fat still makes up about 10 percent of their body weight. From a survival standpoint, this is absolutely critical, since in periods of low food availability or during a famine situation, a person must live off his/her stored body fat or perish. The fact that we are all alive today is proof that our ancestors had bodies that were efficient at storing, and later retrieving, the energy in the body fat.
This is how we obtain energy from the stored body fats. As we have seen, fats are made up of glycerol combined with fatty acids. The glycerol is broken away from the fatty acids, and can then be converted into glucose for immediate use, and to glycogen for storage and later use. About 10 percent of the fat we eat converts to sugars in a process called glyconeogensis (gly-co-KNEE-oh-gen-e-sis).
If you have not read the series of articles I have written on carbohydrate metabolism, go to the Vital Information section of CarbSmart Magazine and read those articles for a better understanding of how glucose and glycogen are used for energy.
Functions Of Dietary Fat: Fats Also Serve As Transporters
Another very important function of fats is the transportation and use of vitamins A, D, E, K, and for other substances which are fat-soluble. Without fat in the diet, those vitamins would not be able to function. This would result in severe problems with eyesight, skin, nail formation, blood clotting, kidney function, bone growth and repair, reproductive functions, and cellular energy. Additionally, some of the fatty acids that make up fats are absolutely necessary for life. They are called essential fatty acids (or EFAs), because they must be eaten.
Fats slow stomach digestion and passage of foods through the intestinal path. This important fat function gives the body the necessary time to absorb the essential nutrients in the protein food, which historically has been in shorter supply.
Today, Western societies have more food than we need, so we tend to forget that in times of food scarcity, the body needed to get everything it could from every bite.
Additional Functions Of Fat
- Fat, in the form of structural body fat, provides important protection for the vital internal organs.
- Fat is a fairly poor conductor of heat, body fat in the subcutaneous tissues (under the skin) acts as insulation and tends to prevent loss of body heat.
- Fats are required for brain structure.
- Substances made from fats also provide the covering for nerves, and thereby allows nerves to carry the impulses necessary to function.
- Fat provides the makeup of the walls of cells, the cell membranes, which are required to allow the passage in and out of essential chemicals.
- Fats are part of the structure of the skin which literally holds us together. The skin is often overlooked as being important for existence, but consider what would happen if the skin were to ‘come apart’ like old fabric.
- Fats are necessary for the production of hormones to regulate and initiate body activities.
- Another function of dietary fats is the stimulation of the flow of bile, and the emptying of the gallbladder. Bile, which we will discuss if further detail as we go along, is important in the body’s elimination of the waste products created by the normal breakdown of red blood cells. If the bile does not leave the gallbladder as it should, gallstones may form.
- Fat is absolutely necessary for milk production in nursing mothers, and is required during pregnancy for the proper development of the child.
- Fat is also necessary for the normal body development of children, once born.
There are other vital functions of fats which I have not mentioned, but from these you can see that, contrary to being a bad thing, dietary fat is very necessary, not only for optimum health, but for life itself.
Next time, we’ll continue talking about fats. We will look at bile and its relationship to dietary fat, and perhaps we’ll have time to start talking about fat digestion.
Join me, won’t you?
*** Note: In the body of the article, you will see several times where the word calorie is spelled Calorie. The capital ‘C’ is required on those words because I am talking about kilocalories.
The Science of Low-Carb & Keto Diets
|About Dr. Beth Gruber
Dr. Gruber is a graduate of the Southern California University of Health Sciences and has been in private chiropractic practice in Long Beach, California since 1964. She also received both a Bachelor’s Degree and a Master’s Degree from California State University at Long Beach. She has written on health-related subjects for over 30 years, for several different publications. She lives in Southern California with her husband of 33 years. Both she and her husband follow and live the low-carb lifestyle full time.
Although some initial fat digestion is done in the stomach, most digestion and virtually all nutrient absorption of fats takes place in the small intestines. The pancreatic enzyme, called pancreatic lipase or steapsin, is the major fat-digesting substance. Article 21 of the Science of Low-Carb & Keto Diets series.