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Proteins combine with phosphoric acid to produce phosphoproteins, such as casein, a protein in milk.
Nucleic acids combine with proteins to create nucleoproteins, essential components of cell nucleus, and protoplasm, the living material inside each cell.
The carbon, hydrogen, and oxygen , left over after protein synthesis is converted to glucose and used for energy. The nitrogen residue (ammonia) is not used for energy. It is processed by the liver, which turns the ammonia into urea. Most of the urea comes from the kidneys in the urine; very small amounts come off the skin, hair and nails.
Everyday, you reuse more proteins than you get from the food you eat, so you need a continuous supply to maintain your protein status. If your diet does not contain enough protein, you will start to digest proteins in your body, including the protein in your muscles- and in extreme cases even your heart muscles.
To make all the proteins that your body needs, you require 22 different amino acids. Nine are considered essential, which means that your body cannot make then and must get them from food.
The rest are nonessential- if you do not get them in food, you can make them yourselves from fats, carbohydrates, and other amino acids.
Because an animal’s body is similar to ours, its proteins contain similar combinations of amino acids. That is why nutritionists call proteins from foods of animal origin – meat, fish, poultry, eggs, and dairy products- high-quality proteins. Our bodies absorb these proteins more efficiently; they can be used without much waste to synthesize other proteins. The proteins from plants- grains, fruit, vegetables, legumes, beans, nuts, and seeds- often have limited amounts of amino acids. Our bodies do not absorb them very easily or use them as efficiently as animal proteins. Their nutrition quality is not as high.
The basic standard against which you measure the value of the proteins in food is the egg. Nutrition scientists have given the egg a biological value of 100 percent, meaning that it is the most useful to the human body. Other foods, which actually have more protein, may not be as valuable as the egg because their proteins are not as complete, which means they lack ample amounts of one or more essential amino acids.
For example, eggs are 11 percent protein; dry beans, 22 percent. But the proteins in beans do not provide sufficient amounts of all the essential amino acids, so they are not as valuable to human beings. The prime exception is the soybean, a legume, which is packed with abundant amounts of all nine essential amino acids. Soybeans are an excellent source of proteins for vegetarians especially vegans, who avoid all animal products not just meat, such as eggs and milk.
An average healthy human adult man or woman needs about 0.8 grams of high- quality protein for every kilogram of body weight, slightly more than 0.4 for every pound. As you grow older, you synthesize new proteins less efficiently, and your muscle mass diminishes while your fat content stays the same or rises. This is why muscle seems to “turn to fat” in old age. END
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