Today we are going to learn more about the wonderful machine—our body. There are machines in industry today that can do wonderful things. They are very efficient and can save us much time and work, but there is no machine that can compare to the human body. One of the very interesting things about this body machine is the way it keeps itself in repair, and that is what we are going to consider now.
Naturally, in every machine that operates there is a certain amount of wear and tear. When the tires wear out on your automobile you put on new ones, if spark plugs get too old you replace them with new ones, or it may be just another screw or bolt that has worn out in its time of service. At this time we are urged to take particular care of our cars. Why not take as good care of our bodies?
The body, too, is constantly having to replace parts, we might say. What we need to do is to supply the material with which to do the repairing, and the body does the work itself. This material for repairing the tissues of our body we call protein.
The muscles of our body are largely protein. That is what they are built from, and that is what has to be supplied to keep them in repair. This protein must be supplied in the food we eat.
Perhaps we can illustrate by the use of these blocks t how the repair process goes on in the body, and appreciate better the miraculous workings of the human body. When protein food is eaten, it is digested in the stomach and intestines into the minutest particles, so small that they can be absorbed right through the lining of the intestines into the blood stream. These particles we call amino acids. Each one of these blocks represents an amino acid. (Build up blocks into pile.) We shall say that this pile of blocks represents the protein found in milk. It could represent the protein found in eggs or cheese as well. What happens when the protein is digested is illustrated by separating the blocks. (Break up pile of blocks into separate units.) We now have a quantity of separate amino acids ready to be absorbed into the blood. These amino acids are absorbed, circulate around in the blood, and are sent out to the various tissues. This blood in its circuit will undoubtedly come in contact with a tissue which has one or more amino acids that have served their day. They are worn out, in other words, and so are discarded—thrown out into the blood stream—and new ones are put in their places.
As the blood circulates through the body, there is a constant exchange of old amino acids for new ones. This is how our tissues are constantly being renewed. You might be interested to know that it takes about seven years for the complete renewal of all the body tissues. It takes about that length of time to make you new all over again. You can very readily see that unless the body is supplied with a sufficient amount of the right kind of protein material, there might not be enough amino acids to make an even exchange, and the result would be a wasting away of that tissue.
We have been talking about repair of tissue which takes place in the adult, but in the growing child entirely new tissue has to be built up. Instead of only a few amino acids being needed for repair, many are needed at the same time to build new tissues in a growing child.
You may have noticed these ten blocks that are colored red. They represent those amino acids which must be included in the diet in order for growth to take place. We call them essential amino acids. It was recently discovered that only eight of these are needed by the adult to keep his tissues in repair because the body can make some of the other amino acids from these essential ones. According to our present knowledge, the best proteins for growth contain all ten of these amino acids.
The proteins containing all these ten essential amino acids are called complete proteins. Other proteins may be lacking in one or more of these ten, and then we say that those proteins are incomplete. This would mean nothing to you unless you knew what foods contain complete protein, and what foods contain incomplete protein. The complete proteins are found in milk, eggs, meat, soybeans, garbanzos, green leaves, and some nuts. The incomplete proteins are found in grains, legumes,vegetables, and fruit.
This does not mean that we should not get some of our protein from these incomplete sources. These are usually very economical sources of protein, and can very well be a part of our protein intake. Not all our protein need be of the complete type, but there must be some, in order to have a supply of all the essential amino acids. This is particularly true of children during the rapid-growing stage.
We have mentioned that a deficiency of protein will result in a wasting of tissue. Such a deficiency during the growing period would lead to stunted growth. (Show pictures of rats representing growth at different levels of protein intake.) There is a possibility that the diet of nonvegetarians may provide too much protein. Especially is this true in adult life after growth has ceased.
You may wonder what happens to the worn-out amino acids after they are thrown into the blood stream. They are taken to the liver, where the nitrogen, which is always present in protein, is taken out ; and the kidney excretes this in different . forms. The rest of the amino acid is put back in the blood and goes out to the tissue to be burned and give us heat and energy.
If we eat so much protein that more amino acids are supplied than are needed for repair, the liver has the work of removing the nitrogen, and the kidneys have the work of excreting the nitrogen products. Therefore extra work is placed on the liver and kidneys. Protein above what is needed for growth or repair is a waste, because it is not stored in the body to be used at some future time. As a rule, people of America eat too much protein rather than too little.
The question we are most interested in then is : How much protein should we have each day? Nutritionists who have studied carefully the body's need for protein have given us this as a standard —one gram per kilogram of body weight per day. Divide the normal body weight in grams by 2.2, because there are 2.2 pounds in one kilogram. It may be easier to remember that a little less than half your normal weight in pounds equals the grams of protein you need each day. ( Show chart demonstrating servings of foods and grams of protein per serving.)
Ask members of the class to suggest a day's menu. Quickly estimate the grams of protein in each food, and tabulate these on the board as the foods are enumerated. Example: (See PDF)
Excessive indulgence in eating and drinking is sin. Our heavenly Father has bestowed upon us the great blessing of health reform, that we may glorify Him by obeying the claims He has upon us. Counsels on Health, p. 50.
* Written when the author was a student of dietetics, in food demonstration class, Loma Linda.
+About forty (or more if desired) one-inch wooden blocks are used to illustrate amino acids. The ten essential amino acids are differentiated from the rest by being painted red.
