Unit 6 The Proteins and Amino Acids - HNSC-1210-D01 - Nutrition for Health and Changing Lifestyles PDF

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U 6: T P  A A I In the world of high protein diets, how much protein do we really need in a day and what are the health consequences of getting too much? Are all proteins created equally, or do some proteins have a higher nutritional quality? And, can you really get all the nutrients your body needs by following a vegetarian diet – what nutrients are of concern and what foods should replace the meat? Proteins play an important role in our health. This unit explores protein synthesis, the digestion/absorption of protein, major functions of protein in the body, and factors that affect protein utilization. You will learn about how the source of protein can affect the quality of the protein, the different states of nitrogen balance, consequences of getting too much and too little protein from the diet, and information on vegetarian eating.

L  Upon completion of this unit, you should be able to do the following: 1. describe the synthesis and structure of protein; 2. describe the process of protein digestion/absorption; 3. discuss the functions of protein in the body; 4. discuss protein utilization and how to prevent protein wasting; 5. identify the dietary recommendation for protein; 6. identify food sources of protein and the protein quality factors; 7. discuss the strategy of mutual supplementation; 8. discuss nitrogen balance and identify populations at each stage of balance; 9. identify the characteristics of the two forms of protein energy malnutrition discussed in the course notes; 10. discuss the consequences of excess protein intake; 11. describe health benefits of a vegetarian diet and an omnivorous diet; and 12. discuss nutrients of concern with poorly planned vegetarian and omnivorous diets.

H   1. Read the instructional content in this unit. You should visit the links included in the course notes and the textbook. 2. Read the textbook chapter (The Proteins and Amino Acids), following along with the instructional content, making notes as you read. (You only need to know the materials, figures and tables from /

the textbook that are covered / mentioned in the instructional content). 3. At the end of the unit, test your knowledge of the material by trying the practice questions at the end of the chapter and/or on the textbook companion website CourseMate. 4. Complete the timed quiz for unit 6. 5. Read through Assignment 2 and begin entering your foods into EATracker.

I  P  A A Proteins are compounds made up of Carbon, Hydrogen, Oxygen and Nitrogen. Some of our body’s proteins are working proteins: enzymes, antibodies, hormones, oxygen carriers, etc. Others are structural proteins: tendons, ligaments, fibres of muscles, found in our bones, teeth, hair and nails. Proteins are arranged in strands of amino acids. Amino acids are the building blocks of proteins. The amino acids in a strand differ from one another – a protein strand could have twenty different amino acids! All amino acids have the same chemical backbone: a single carbon atom, with an amine group and an acid group attached. Each amino acid has a distinctive side chain which gives it its identity and chemical nature. The side chains make the amino acids differ in size, shape and electrical charge (positive, negative or neutral). See Figure “An Amino Acid”. About 20 amino acids make up most of the proteins of living tissues. There are a few additional amino acids that rarely appear in a few proteins. The body can make about half of the 20 amino acids itself, however some are essential, meaning that the healthy body cannot make those amino acids or cannot make enough to meet the body’s needs. These amino acids must be derived from foods so that the body can make the proteins it needs (TV TILL PM: Tryptophan, Valine, Thronine, Isoleucine, Leucine, Lysine, Phenylalanine, Methionine). The body is also able to recycle amino acids by breaking apart food proteins after digestion, and body proteins after they have completed their cellular work. This allows for an emergency supply of amino acids for times of fuel, glucose or protein deprivation. However, this will sacrifice the working muscle tissue – using the most dispensable muscles first and leaving the organs and heart protein until dire need. Amino acids are joined together by peptide bonds to form proteins. See Figure “Different Amino Acids Join Together” 2 amino acids = dipeptide (See Figure “A Dipeptide and Tripeptide”) 3 amino acids = tripeptide >3 amino acids = polypeptide /

Several dozen to 300 amino acids join to form a protein. The strand of protein does not remain in a straight chain. The electrical charges of the amino acids (caused by the side chain) cause the strand to bend and coil, as amino acids attract and repel one another. This forms either a globular shape or fibrous shape. See Figure “The Coiling and Folding of a Protein Molecule” The amino acids with electrically charged side chains attract water and are oriented on the outside of the protein structure. The neutral amino acids repel water and are attracted to one another, so orientate in the centre of the protein away from body fluids. These interactions give each protein a unique structure.

P  The specific structure/shape of proteins enables them to perform different tasks in the body. Some protein strands function alone, while others associate with other proteins in order to become active. There is a vast array of different proteins: the textbook uses the analogy of the alphabet; there are 26 letters that make up millions of words. There are 20 main amino acids that can be combined in many different ways. A single human cell can contain as many as 10,000 different proteins! We are all unique from one another because of minute differences in our body proteins. These differences are determined by the amino acid sequences of the protein, which are written into our inherited genetic code. The unique combination of genes directs the making of the body’s proteins. See Figure “Protein Synthesis” Our genes determine the sequence of amino acids in each finished protein. Different sequences account for genetic diseases, e.g., sickle cell disease. See Figure “Normal Red Blood Cells and Sickle Cells”. For each protein, there exists a standard amino acid sequence which is specified by heredity. If a wrong amino acid is inserted, it can result in disastrous health consequences. Sickle-cell disease is a condition where hemoglobin (the oxygen carrying protein of the red blood cells) is abnormally shaped, and therefore loses its function to carry and release oxygen. This is because one of the protein strands contains valine as the 6th amino acid instead of glutamic acid. If too many crescent shaped cells appear in the blood, abnormal blood clotting, strokes, susceptibility to infection, severe pain and early death can occur.

P  See Figure “How Protein in Food Becomes Amino Acids in the Body” When a person eats food proteins from any source, the body must first alter them by breaking them down into amino acids. Then it can rearrange them into specific human body proteins. Protein digestion starts in the stomach. The gastric acid denatures the protein, meaning that it changes the shape of the protein strand, opening it up to allow digestive enzymes to cleave/break the peptide bonds.

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Denaturing Proteins audio file

By the time most proteins enter into the small intestine, they are broken into smaller pieces (a few single amino acids and a majority are polypeptides). Protein digesting enzymes from the pancreas and the intestine split the polypeptides into di and tripeptides and single amino acids. Enzymes on the surface of lining of the small intestine split the di and tripeptides, allowing the intestinal cells to absorb and transfer the amino acids to the bloodstream. Once in the bloodstream, the amino acids are transported to all of the body’s cells. Sometimes, larger peptide molecules escape the digestive process and enter the bloodstream intact. It is thought that these larger molecules may act as hormones to regulate body functions, and provide information to the body about the external environment. These large molecules may also stimulate an immune response, thus playing a role in food allergies.

P  The cells of the small intestine possess separate sites to absorb different types of amino acids. Amino acids of the same type compete for the same absorptive sites. Therefore, consuming a large dose of any amino acid may limit the absorption of other amino acids of the same general type. This is one reason to take caution against taking single amino acids as supplements. Once the amino acids are circulating in the bloodstream, they travel to the liver where they are used or released back into the blood to be taken up by other body cells. The cells can then link the amino acids together to make proteins that they keep for their use or release into the lymph or blood for other uses. The body can also use amino acids for energy if necessary.

F   See Table “Summary of Functions of Proteins” The following represents only a sampling of the many roles that proteins can play. Supporting Growth & Maintenance: Amino acids must be continuously available to build proteins of new tissue (e.g., these tissues may be in the muscles of an athlete, in a growing child, in an embryo, in the scar tissue that heals wounds, etc). Protein also helps to replace worn out cells and internal cell structures (e.g., red blood cells only live for 34 months, then they must be replaced by new cells produced by the bone marrow. The cells lining the digestive tract only live for 2-3 days, so are constantly being shed and replaced). So, the body needs dietary amino acids to grow new cells and replace worn-out ones.

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Building Enzymes, Hormones and Other Compounds: Enzymes are among the most important proteins formed in living cells, acting as a catalyst to speed up specific chemical reactions. See Figure “Enzyme Action”. Some of the body’s hormones are made from amino acids. Hormones help to regulate body conditions; for example thyroid hormone (thyroxine) regulates the body’s metabolism. Insulin is another example of a hormone made from amino acids. Building Antibodies: Antibodies attack foreign particles, while recognizing the body’s own proteins and leave them alone. Each antibody is designated to destroy one specific invader. Therefore, the antibodies used to fight one strain of the flu will not be effective against another strain. The body remembers how to make the antibody again, therefore developing immunity to the invader. Maintaining Fluid and Electrolyte Balance: Proteins do this by regulating the quantity of fluids in the compartments of the body. Cells must maintain a constant amount of fluid to remain alive. Although water can diffuse freely in and out of cells, proteins cannot and they attract water. By maintaining stores of internal proteins, this helps cells to retain the fluid they need. If this system fails (e.g., protein deficiency), too much fluid collects in the spaces between the cells of tissues, causing edema (fluid buildup). Transport proteins also hold electrolytes in their proper chambers. See Figure “Proteins Transport Substances Into and Out of Cells”. Maintaining Acid-Base Balance: Blood proteins act as buffers to maintain the blood’s normal PH. They do this by picking up hydrogen molecules (acid) when there are too many in the blood stream, and releasing them when there are too few. Clotting of Blood: Special blood proteins respond to injury by forming a stringy net that traps blood cells to form a clot. The clot acts as a plug to stop blood flow from the wound. Proteins are also involved as the wound heals; the protein collagen replaces the clot with scar tissue. Providing energy and glucose: Under normal conditions, protein provides very little energy. When the diet is deficient in CHO or total energy, protein use speeds up. So this is a secondary function for protein. See Figure “Three Different Energy Sources”. Protein is broken down into energy and nitrogen, which is either used or sent to the liver where it is converted to urea and then sent to the kidneys for excretion in the urine. The fragments that remain are carbon, hydrogen and oxygen, which can be used to build glucose or fatty acids. Because amino acids can be converted to glucose, protein can help to maintain a steady blood glucose level and serve the glucose needs of the brain as need arises. There is no specialized protein storage area in the body. When body amino acids are required for energy, the body must dismantle its tissue proteins, leading to lean body tissue wasting. If the body takes in excess amino acids, the body cannot store them. It will remove and excrete the amine group, and use the remaining fragments to support the body’s energy needs, convert to glucose for storage as glycogen, or convert to fat for storage.

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When an amino acid arrives at a cell, it can be used in one of several ways. 1. It can be used to build part of a growing protein 2. It can be altered to make another needed compound (e.g., the amino acid tryptophan can be converted to make niacin (a B vitamin we will look at further in unit 8) 3. The cell can dismantle the amino acid in order to use the amine group to build a different amino acid. After the amine group is removed, the remainder can be used for energy or converted to glucose or fat for storage. If the body is not using the amine group to create a different amino acid, it will be excreted from the cell, and then from the body as urine. Amino acids are considered wasted when they are not used to build protein or other nitrogen-containing compounds. This occurs if any of these 4 conditions exists: 1. When the body does not have enough energy from other sources 2. When the diet provides more protein then the body needs 3. When the diet has too much of any single amino acid (such as from supplements) 4. When the diet supplies protein of low quality, with too few essential amino acids. To prevent the wasting of dietary protein and allow for the synthesis of needed body protein, dietary protein must be: 1. Adequate in quantity 2. Supply all essential amino acids in the proper amounts 3. And must be accompanied by adequate energy from CHO and fat.

F F: G E B N T M P Protein is found in all four food groups. Foods in the Meat and Alternatives, and the Milk and Alternatives food groups contribute an abundance of high-quality protein. Smaller amounts of protein are also contributed by the Vegetables and Fruit, and the Grain Products food groups. See Figure “Finding the Protein in Foods” See Figure “Major Sources of Protein in the Canadian Diet”

P R See Table “Recommendations Concerning Intakes of Protein and Indispensable / Essential Amino Acids for Adults” Most people in developed countries eat more than ample protein. When you analyze your protein intake for your third assignment, many of you will find that your intake exceeds the DRI recommendations. DRI: 0.8g/kg body weight; so for an average women: 46g/day, average men: 56g/day. DRI Acceptable Macronutrient Distribution Range (AMDR): 10-35r% total energy /

P Q  Q The response of the body to dietary protein depends on many factors, including the body’s state of health, other nutrients and energy consumed at the same time, and the protein’s quality. In malnutrition, digestive enzymes secretion slows as the digestive tract lining degenerates, impairing protein digestion and absorption. With infection, additional protein is required to enhance immune function. For efficient use of protein, it must be accompanied by the full array of vitamins and minerals. Protein quality helps to determine how well a diet supports the growth of children and the health of adults. It is influenced by the digestibility of the protein and its amino acid composition. 1. Digestibility: In general, amino acids from animal protein are most easily digested and absorbed (>90% of protein absorbed). Legumes are next (~80-90%) followed by grain and plant proteins (7090%). Cooking with moist heat (e.g., steaming or poaching) improves protein digestibility, where as dry heat methods (e.g., broiling) can impair it. 2. Amino acid composition: High quality proteins are ones with ample amounts of all essential amino acids. Low quality proteins do not. Within a single day of restricting essential amino acid intake, the body starts to limit the break down of working proteins and reduce amino acid use for fuel to conserve the essential amino acids it currently has.

A diet short in any of the essential amino acids limits protein synthesis. In building a protein, no other amino acid can fill another’s spot. If a cell building a protein cannot find a needed amino acid, protein synthesis stops and the partial protein is released. These partially completed proteins are not stored until the amino acid is available. They are instead dismantled and the amino acids are released back into circulation. They are either picked up by other cells, or are dismantled and used for other purposes.

Complimentary Proteins audio file

See Figures "Complementary Protein Combinations" and "Proteins that Complement Each Other Work Together"

N B See Figure “Nitrogen Balance” Protein recommendations are based on nitrogen balance studies, which compare nitrogen lost through excretion with the nitrogen eaten in food. Under normal circumstances, healthy adults are in nitrogen equilibrium, meaning they have roughly the same amount of protein in their body at all times. /

Positive nitrogen balance: Nitrogen in exceeds nitrogen out. Somewhere in their bodies, more protein is being built than are being broken down (e.g., growing children, pregnant women). Negative nitrogen balance: Nitrogen out exceeds nitrogen in. Muscle or other protein tissue is being broken down and lost (e.g., illness, injury. Also astronauts: stress of space flight and no need to support body’s weight against gravity causes muscles to weaken and waste).

P E M The combination of protein deficiency and energy deficiency, protein energy malnutrition (PEM) is the world’s most widespread form of malnutrition. Over 500 million children face impending starvation and suffer the effects of severe malnutrition and hunger. Worldwide, 33,000 children die every day, many of whom are malnourished. PEM is more prevalent in Africa, Central America, South America, the Middle East, and East and West Asia, however we are not immune to it in North America (often associated with chronic disease, poverty, eating disorders). PEM strikes early in childhood often causing stunted growth, however affects adults as well (leading to weight loss and wasting). We are going to review two forms of PEM: Marasmus and Kwashiorkor. See Table “Features of Marasmus and Kwashiorkor in Children”

Marasmus reflects chronic inadequate food intake, a total diet deficiency. It is a slow, chronic form of PEM. Marasmus is seen in children 6-18 months of age who live in overpopulated city slums. Malabsorption occurs because digestive enzymes are in short supply and digestive tract lining deteriorates. A child experiencing Marasmus suffers from severe weight loss, including muscle and fat loss. The child appears very thin in appearance (one characteristic seen is “matchstick thin” arms). Muscles (including heart muscles) weaken and brain development is stunted and learning impaired. The hair becomes sparse, thin, dry and pulls out easily. The skin becomes dry, thin and wrinkled (like an elderly person). An infection of the intestinal tract which causes diarrhea (dysentery) can occur, causing further depletion of nutrients. The rate of infections increases and Kwashiorkor often follows because the body is using more protein to try to fight infection. ...