Chapter 5 Medicine Goals

Proteins are large, complex molecules that re critical components of all tissues, including muscle, blood, and bone. Like carbohydrates and fat, they contain carbon, hydrogen, and oxygen. In contrast, however, the structure of proteins is dictated by DNA, and proteins contain nitrogen. Amino acids are the building blocks of proteins; they are made up of a hydrogen atom, an acid group, an amine group containing nitrogen, and a unique side chain. There are 20 amino acids in our bodies: 9 are essential amino acids, meaning that our bodies cannot produce them, and we must obtain them from food; and 11 are nonessential, meaning our bodies can make them, so they do not need to be consumed in the diet.

Our genetic makeup determines the sequence of amino acids in our proteins. Genes carry the instructions that cells use to make proteins. The three-dimensional shape of proteins determines their function in the body. When proteins are exposed to damaging substances such as heat, acids, baes, and alcohol, they are denatured, meaning they lose their shape and function. A limiting amino acid is one that is missing or in limited supply, preventing the synthesis of adequate proteins. Incomplete proteins, also known as low-quality proteins, do not contain all the essential amino acids in sufficient quantities to support growth and health. Complete proteins, also known as high-quality proteins, have all nine of the essential amino acids and can therefore support growth and health.

Mutual supplementation is the process of combining two incomplete protein sources to make a complete protein. The two foods in this process are called complementary proteins. Non-meat food combinations that provide complete proteins include legumes when served with either grains or nuts and seeds.

Proteins are needed to promote cell growth, repair and maintenance. They act as enzymes and hormones; help maintain the balance of fluids, electrolytes, acids, and bases; transport nutrients and other substances; and support healthy immune function. They can be used for energy if intake of carbohydrate and fat is inadequate to support energy needs.

In the stomach, proteins are denatured by hydrochloric acid, and pepsin begins breaking the proteins into smaller polypeptides and single amino acids. Most digestion of proteins occurs in the small intestine with the help of proteases. These break the polypeptides into tripeptides, dipeptides, and single amino acids, which are absorbed into the enterocytes. These break the remaining peptides into amino acids. The amino acids are transported into the blood stream to the liver and on to cells throughout our body as needed. Protein digestibility affects its quality, with those proteins that are more digestible being of a higher quality. Animal sources, soy protein, and legumes are highly digestible forms of protein.

The RDA for protein for sedentary people is 0.8 grams of protein per kilogram body weight per day. To calculate your protein needs, start by converting your weights from pounds to kilograms by dividing your weight in pounds by 2.2. Next, multiply by 0.8. The AMDR for protein is 10% to 35% of total energy. Most people in the United States routinely eat 1.5-2 times the RDA for protein.

Protein-energy malnutrition can lead to marasmus and kwashiorkor. These disease primarily affect impoverished children in developing nations. However, residents of developed countries are also at risk, especially the elderly, the homeless, people struggling with substance abuse, and people with AIDS, cancer, and other wasting diseases.

Healthful sources of protein include lean meats, poultry, fish, low-fat dairy products, eggs, soy and other legumes, quinoa, and nuts, as well as plaint-based meals combining complementary proteins.

There are many forms of vegetarianism, from flexitarians (semi-vegetarians) who may occasionally eat meat, to vegans, who eat no form of animal product. Consuming a well-planned vegetarian diet may reduce the risk of obesity, high blood pressure, heart disease, type 2 diabetes, certain intestinal problems, kidney disorders, and gallstones. Some research suggests that it may also reduce the risk for some forms of cancer. Vegans may need to supplement their diet with vitamins B12, and D, riboflavin, iron, calcium, and zinc.