All protein in your body is formed from compounds called amino acids. Twenty amino acids form numerous combinations to create the 50,000 kinds of proteins needed to make up every cell in your body. Nine amino acids can only be gotten through diet, but your body is able to make the others.
Protein Basics
When you eat protein in food, your body breaks it down into its component amino acids. Your body then uses those amino acids to create the protein needed to build cells, tissues, organs, hormones, neurotransmitters and enzymes -- in other words, everything that makes up your body. Protein consumption should be about 10 to 35 percent of your total daily calories. Children ages 1 to 3 should consume 13 g of protein each day, while children ages 4 to 8 should eat 19 g. Due to the growth spurts and maturation of pre-adolescence and adolescence, that amount nearly doubles to 34 g for ages 9 to 13, then increases to 46 g for girls and 52 g for boys up to age 18. Requirements level off a bit in adulthood to 46 g for women and 56 g for men.
Essential Amino Acids
The nine amino acids that cannot be made by your body are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. A 10th amino acid that is essential for the very young is arginine. When a food protein contains the nine essential amino acids, it is said to provide "complete" protein.
Nonessential Amino Acids
The remaining 10 amino acids fall into two categories called nonessential and conditional. The four nonessential amino acids are alanine, asparagine, aspartic acid and glutamic acid. The term "nonessential" does not mean you don't need them, but only that your body can make them whether or not you eat them in food.
Conditional Amino Acids
The conditional amino acids are cysteine, glutamine, tyrosine, glycine, ornithine, proline and serine. You need them during periods of stress or illness. Your body makes conditional amino acids, as long as the raw materials are present. For example, the conditional amino acid tyrosine is made from the essential amino acid, phenylalanine, underscoring the importance of getting the essential amino acids through your diet.
Dietary Sources of Protein
Protein is present in meat, poultry, fish, legumes, eggs, dairy products, soy products, nuts, seeds, grains and some vegetables. Protein is categorized as complete or incomplete based on whether it contains the essential amino acids. Complete protein contains all of the essential amino acids and is present in foods from animal sources as well as in soy and the grain quinoa. Incomplete protein is present only in foods from plant sources. However, foods from different plant sources will contain large amounts of some amino acids and none of others, but the content is not the same for every food. By combining these complementary proteins, you can get all of the essential amino acids even on a vegetarian diet.
Member Comments