Lec 3 - Proteins PDF

Proteins  Learning goals 1. Compare and contrast proteins to the other energy containing macronutrients. 2. List the essential amino acids. 3. Explain the differences between high-quality and low-quality proteins, how they can be quantified using the protein digestibility corrected amino...

Proteins  Learning goals 1. Compare and contrast proteins to the other energy containing macronutrients. 2. List the essential amino acids. 3. Explain the differences between high-quality and low-quality proteins, how they can be quantified using the protein digestibility corrected amino acid score (PDCAAS) and how to overcome the limits of low- quality protein using mutual supplementation. 5. Identify some of the roles of body proteins. 6. Explain the process of protein turnover and describe nitrogen balance. 7. Understand Health Canada’s recommendations as it relates to total protein and the challenges faced by vegetarians. 48  Comparison to lipids and CHO Contain the same atoms as carbohydrates and lipids- carbon (C), hydrogen (H) and Triglyceride oxygen (O) atoms, but proteins are different in that they also contain nitrogen (N) atoms Energy producing when there is a shortage of fats or carbohydrates, proteins can also yield energy Synthesized in the body dictated by genetic code 50  Base unit - amino acid All amino acids share common chemical “backbone” that forms the protein Each amino acid composed of amine (-NH2, containing nitrogen) and carboxylic acid (-COOH) functional groups, a hydrogen atom and a distinctive side chain (R-group), all linked to the same central carbon atom Each amino acid carries a distinctive side group that varies from one amino acid to another Side chain (R-group) makes the amino acids differ in size and shape 51  Need to know the 9 essential Amino ac Amino acids 20 different amino acids Essential amino acids Essential (also known as These amino acids must be consumed in the diet. indispensable) Histidine body cannot synthesize at all Isoleucine or in sufficient quantities to Leucine meet need has to come from diet Lysine 9 amino acids Methionine Phenylalanine Threonine Tryptophan Valine 52  Amino acids Transamination (creates the non-essential amino acids for essentail) – * transfer the amine (NH2) group from one amino acid to another molecule (keto acid, amino acid without an amine group) to make a new amino acid and a new keto acid * - catalyzed by a group of enzymes called transaminases, and occurs mostly in liver - can convert an essential to nonessential amino acid 54  Amino acids Conditionally essential; an amino acid that is normally nonessential but must be supplied by the diet in special circumstances when the need for it becomes greater than the body’s ability to produce it: nonessential amino acid (e.g. tyrosine) becomes essential amino acid body cannot make the conversion ex. phenylalanine X tyrosine (Phenylketonuria, PKU) 55  How are proteins made? Link amino acids to form peptides condensation reaction to form a peptide bond (release of water) Dipeptide: two amino acids bonded together 56  How are proteins made? Additional amino acid to dipeptide becomes a tripeptide (three amino acids bonded together) Additional amino acids to tripeptide become a polypeptide (10 or more amino acids bonded together) Most proteins are 30-300 amino acids long 57 Protein synthesis Individuals have different proteins Proteins have different amino acid sequences Amino acid sequence is determined by genes (DNA) 58  Protein synthesis Synthesis limiting improper combination and quantity of essential (limiting) amino acids – incomplete or low-quality protein source limiting amino acid : is an essential amino acid that is present in dietary protein in the shortest supply relative to the amount needed for protein synthesis in the body inadequate energy consumption (amino acids used for gluconeogenesis) 59  Protein organization Sequence of amino acids is unique to all proteins 10,000-50,000 different kinds of protein Amino acid side chain (sequence) determines protein shape determines protein function 60  Protein Susceptible to denaturation (need to know) lose function destroy all structure except primary (need enzymes to hydrolyze) agents such as heat (e.g. cooking), acid (e.g. vinegar) 61  Digestion - Protein Mouth and salivary glands -chewing protein foods and mix them with saliva to be swallowed Stomach Hydrochloric acid (HCl): denatures proteins Pepsin: activated by HCl and cleaves proteins into smaller polypeptides 62  Absorption - Protein Intestinal tripeptidases and dipeptidases; break down tripeptides and dipeptides into amino acids Intestinal cells absorb some dipeptides and tripeptides amino acids Small intestine is the primary site of amino acid absorption into the blood Amino acids are transported directly to the liver through the portal vein; can then be used to either make proteins or are broken down to produce glucose In case of excess of dietary protein, after absorption, the extra amino acids will be rapidly metabolized, and the nitrogen will be excreted. 64  Absorption – Protein Different sites on intestinal cells specialized in transporting specific amino acids Competitive inhibition consumption of too much of one amino acid (supplementation) may inhibit absorption of another 65  Incomplete protein Protein in foods Complete protein does not contain all nine contains all nine essential essential amino acids considered “low quality” amino acids considered “high quality” plant sources (e.g. legumes) animal sources (e.g. egg) and soy (e.g. tofu, soy milk) 66 Protein in foods Two factors determine protein quality or completeness: 1. Amount of essential amino acids 2. Protein digestibility 67  Protein in foods Amount of essential amino acids (amino acid score) compared against reference (requirements for preschool-age children, age 1 year and older) Do not need to know numbers, 68  Amino acid score - beans Essential Amino acid Amino acid of Score amino acid of food (mg/g reference (mg/g protein) protein) Histidine 30 18 1.67 Isoleucine 42.5 25 1.7 Leucine 80.4 55 1.46 Lysine 69 51 1.35 Methionine (+ 21.1 25 0.84 This is the first cysteine) limiting amino Phenylalanine (+ 90.5 47 1.93 acid tyrosine) Threonine 43.7 27 1.62 Tryptophan 8.8 7 1.26 Valine 50.1 32 1.57 69  Protein in foods Protein digestibility animal foods are highly digestible (90-99%) soy foods are highly digestible (>90%) other plant foods are less digestible (70-90%) 70  Protein in foods Protein digestibility-corrected amino acid score (PDCAAS) PDCAAS = amino acid score (based on amount of essential amino acids) X protein digestibility - The method is based on comparison of the concentration of the first limiting essential amino acid in the test protein with the concentration of that amino acid in a reference (scoring) pattern - Limiting amino acid: an essential amino acid that is present in dietary protein in the shortest supply relative to the amount needed for protein synthesis in the body 71 PDCAAS It is the amino acid score corrected for the digestibility of the protein It is a method of evaluating the protein quality based on both the amino acid requirements of humans and their ability to digest it. The PDCAAS rating was adopted by the US Food and Drug Administration (FDA) and the Food and Agricultural Organization of the United Nations/World Health Organization (FA/WHO) in 1993 as the “preferred best” method to determine protein quality 72  PDCAAS PDCAAS = amino acid score X protein digestibility amino acid score: mg of limiting amino acid in 1 g of test protein / mg of same amino acid in 1 g of reference protein protein digestibility: fecal true digestibility percentage Example: Beans = (21.1/25)* x 0.79 = 0.84 x 0.79 = 0.66 *See Amino acid score-beans table (slide 80) 73 Do not need to know numbers but do need to know the equation calculation  Do not need to know numbers but understand what they m PDCAAS Food item PDCAAS value Casein (milk protein) 1.00 PDCAAS values: from Egg white 1.00 0 to 1 Soybean isolate 0.99 Beef 0.92 Complete Pea flour 0.69 proteins (e.g. Kidney beans 0.68 casein) have Chickpeas 0.66 PDCAAS Pinto beans 0.66 values of Oats 0.57 1.00 Lentils 0.52 Whole wheat 0.40 74  Protein in foods Protein Quality High-quality proteins Provide all essential amino acids to support body’s work Digestibility Depends on protein’s source (e.g. animal source) and other foods consumed together with it Amino acid composition To prevent protein breakdown, dietary protein must supply at least the nine essential amino acids Generally, proteins derived from animal foods 75  Very important to know Protein in foods Mutual supplementation obtain complete amino acid requirements from two or more incomplete protein sources complementary proteins: two or more proteins whose amino acids complement each other - essential amino acids missing from one are supplied by another. 76  Need to know this example - Legumes (e.g. beans, lentils) provide plenty of isoleucine (Ile) and lysine (Lys) but are short in methionine (Met) and tryptophan (Trp). - Grains (e.g. rice) have the opposite strengths and weaknesses, making them a perfect match for legumes. 77  Roles of body proteins Structural components. Proteins form integral parts of most body tissues and confer shape and strength on bones, skin, tendons, and other tissues. Structural proteins of muscles allow movement. Enzymes. Proteins facilitate chemical reactions. Transporters. Proteins transport substances such as lipids, vitamins, minerals, and oxygen around the body. Fluid and electrolyte balance. Proteins help to maintain the distribution and composition of various body fluids. Acid-base balance. Proteins help maintain the acid-base balance of body fluids by acting as buffers. 78  Roles of body proteins Antibodies. Proteins inactivate disease-causing agents, thus protecting the body. Hormones. Proteins regulate body processes (e.g. metabolism). Some, but not all, hormones are proteins. Energy and glucose. Proteins provide some fuel, and glucose if needed, for the body's energy needs. Other. The protein fibrin creates blood clots; the protein collagen forms scars; the protein opsin participates in vision. 79  Protein Turnover and Nitrogen Balance Within each cell of the body, proteins are continually being made and broken down, a process known as protein turnover Amino acids must be available to build proteins of new tissues (e.g. muscle tissue in athletes) 80  Protein Turnover and Nitrogen Balance Protein Turnover When proteins breakdown, their component amino acids are liberated within the cells or released into bloodstream Some of these amino acids are recycled into other proteins Through re-use of amino acids, the body conserves and recycles a valuable commodity 25% of available amino acids are stripped of their nitrogen and used for energy Amino acids from food are needed for new growth and maintenance of cells 81  Protein Turnover and Nitrogen Balance Nitrogen Balance Nitrogen intake from protein in food balances with nitrogen excretion via urine Positive nitrogen status - Body synthesizes more than it degrades - Growing children, pregnant women, and other life stages Negative nitrogen status Occurs in the starving, and people who have severe burns, injuries, infections, or fever (increased excretion of nitrogen) Protein needs can be determined by measuring nitrogen balance 82  How much protein should we eat? AMDR for adults is 10%-35% of daily caloric intake RDA dependents on activity age health status 83  How much protein should we eat? More accurate estimate of protein is based on body weight (0.8 g/kg body weight) NEED TO KNOW People who require more protein include: infants and children – 0.95-1.5 g/kg/day adolescents – 0.85-0.95 g/kg/day pregnant or lactating women – 1.1 g/kg/day vegetarians – 0.9-1 g/kg/day athletes – 1.2-1.7 g/kg/day 84  Calculating energy content With a daily Need to convert g to kcal 344 g X 4 kcal/g = 1376 kcal CHO dietary intake of 100 g X 9 kcal/g = 900 kcal lipids 344 g of CHO, 100 50 g X 4 kcal/g = 200 kcal protein g of lipids, and 50 CHO + lipids + protein = 2476 total kcal g of protein, does the lipid and Compare kcal of individual macronutrient protein intakes meet Health to total kcal Canada’s 1376 kcal CHO / 2476 total kcal = 56% recommendations 900 kcal lipids / 2476 total kcal = 36% ? (above the lipid recommendations of 20%-35% ) 200 kcal protein / 2476 total kcal = 8% (below the protein recommendations of 10%-35%) 85  Dietary protein The risks of too little protein: protein-energy malnutrition when the diet delivers too little protein, too little energy, or both utilize protein for energy children most seriously affected 86  Dietary protein The risks of too much protein may include: high cholesterol and heart disease diets high in protein from animal sources have high saturated fat and cholesterol possible bone loss high protein diets may cause excess calcium excretion leading to bone loss – offset with higher dietary calcium kidney disease high protein diets may be associated with an increased risk of kidney disease (“over-worked” kidneys) especially for people who may be susceptible to kidney disease family history diabetes 87  Vegetarianism Some people choose not to eat meat: religion, ethics, food safety, ecology health reduced risk of overweight (↓ fat and calories) reduced risk of CVD (↓ SFA) reduced GI problems (↑ fibre) reduced risk of cancer reduced risk of kidney disease (moderate protein intake) 89  Be aware of the differing types Vegetarianism Vegetarianism: Type of diet Food consumed Comments restricting the diet to Semivegetarian Vegetables, nuts, grains, legumes, sometimes Typically excludes red meat; sometimes avoids other foods, mostly of plant seafood, poultry, eggs and meat dairy origin Pescovegetarian Similar to semivegetarian Seafood is the only animal there are many but excludes poultry meat consumed as source of protein versions Lacto-ovo- Similar to pescovegetarian Only consumes animal by of vegetarianism vegetarian but excludes seafood products, not meat Dietitians of Canada Lactovegetarian Similar to lacto-ovo- vegetarian but excludes “Vegetarian eating eggs is a healthy Ovovegetarian Similar to lacto-ovo- vegetarian but excludes approach to eating, dairy provided you choose Vegan Only plant-based diet Maybe deficient in vitamin B12, zinc, iron, and calcium well” 90 Vegetarianism-protein Use soy products (e.g. tofu, only complete plant protein source) Eat complementary protein sources (e.g. beans or lentils with rice) Adequate energy source from other macronutrients to spare protein If diet includes animal derived foods such as milk and eggs, there is not a problem with protein deficiency Vegan diet which includes only plant-based foods can provide sufficient amount of protein, as long as energy intake is adequate, and protein sources are varied 91  Vegetarian sources of key nutrients Many plant proteins do not contain all the essential amino acids in the amounts and proportions needed by human beings. To improve protein quality, vegetarians can eat grains and legumes together, for example, although it is not necessary if 92