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Protein and Amino Acids in Sports Nutrition Rookie Module 1 Functions of Proteins Enzymes – All biological enzymes are made of protein • For example, the digestive enzymes trypsin and amylase Hormones (some) – Insulin and glucagon – Not all hormones are proteins • Testosterone is a steroid Structural – Actin & myosin (muscle) – Collagen (skin) Lesk AM. Introduction to Protein Science: Architecture, Function, and Genomics. 2nd ed. New York, NY: Oxford University Press USA.; 2010. 2 Functions of Proteins (cont’d) Immunologic – All antibodies Transport and storage – Carriers of fatty acids, oxygen (hemoglobin), iron, vitamin A, copper, and other nutrients – Cholesterol and triglycerides carried by lipoproteins pH buffering – In blood, muscle, essentially everywhere Energy source – When carbohydrates are limited (gluconeogenesis) Lesk AM. Introduction to Protein Science: Architecture, Function, and Genomics. 2nd ed. New York, NY: Oxford University Press USA; 2010. 3 Structure of Proteins Proteins are made of individual “building block” units called amino acids (AAs) that are linked together – A chain of AAs is called a peptide – Long peptides are proteins The order of the AAs allows different proteins to have different functions Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002. 4 What Are Amino Acids? Building blocks of proteins – Body uses 20 different amino acids to make proteins 9 of the 20 amino acids must be consumed in the diet (essential amino acids; EAA) – Body cannot make them on its own Leucine Isoleucine Tryptophan Threonine Methionine Lysine Valine Histidine Phenylalanine Other 11 amino acids are not essential (NEAA) – Can be made from other amino acids in the diet Some NEAAs can become EAAs under certain conditions – Infants have different needs for growth – Defects in amino acid metabolism • Tyrosine can become essential in individuals with phenylketonuria (PKU), an inborn error of phenylalanine metabolism Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002. 5 Basic Structure of an Amino Acid Central carbon atom (alpha carbon [Cα]) linked to – – – – Amino group (positive) Carboxylic acid group (negative) Hydrogen Distinctive side chain (R) • Makes each AA different – + Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002. 6 R Groups for Some Amino Acids H- Glycine CH3- Alanine H3C HO-CH2CH3-CH- Serine Threonine OH CH- Valine H3C CH2- H3C SH CH-CH2- Cysteine Leucine H3C CH2-CH2Methionine S-CH3 CH2 CH2 CH- Isoleucine -OOC-CH 2 Aspartic acid CH3 Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002. 7 Protein Digestion and Absorption 8 Protein Digestion Gastric phase (stomach) Hydrochloric acid (HCl) from cells in stomach unfolds protein Pepsinogen (chief cells) Pepsin digests proteins HCl Pepsin (enzyme) Large peptide fragments Small intestine phase Cholecystokinin (hormone released in upper small intestine) triggers pancreas to secrete digestive enzymes once digestion products leave the stomach Digestive enzymes are activated and continue to break down peptides into di-/tripeptides and free amino acids, which are taken up by intestinal cells Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002. 9 Amino Acid and Peptide Absorption Intestinal cells have various transport proteins at both the luminal side and the blood side to give AAs and peptides access to the circulation Lumen Transporters Intestinal cell Blood Amino acids Peptidases Oligopeptides Tripeptides Dipeptides Cellular membrane Transporters can carry – Free AAs – Di- and tripeptides • For example, can transport carnosine, a dipeptide – Nonprotein AAs • For example, can transport creatine from intestine to blood Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002. 10 Fast Versus Slow Digestion of Proteins Proteins are digested at different rates – Similar to glycemic index concept for carbohydrates Whey versus casein – Whey is rapidly digested and results in quick rise in plasma AAs (fast protein) – Casein forms a curd and takes longer to empty from the stomach (slow protein) • Less dramatic, but more sustained rise in plasma AAs after consumption Soy protein – Digested faster than whole milk protein, which contains both whey + casein • Overall, more like a fast protein, but slower than whey Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002. Boirie Y, et al. Proc Natl Acad Sci U S A. 1997;94(26):14930-14935. Rossi AL, et al. J Nutraceuticals, Functional and Medical Foods. 2000;3(1):33-44. 11 Nutrition and Cellular Synthesis of Protein 12 Transcription of DNA for Making Cellular Proteins Transcription of DNA – Makes the template (mRNA) for synthesizing proteins – Sequence of mRNA bases (A, C, G, & U) arranged in units of 3 that “code” for specific amino acids Nucleus DNA Rough ER mRNA A, adenine; C, cytosine; G, guanine; U, uracil; ER, endoplasmic reticulum. Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002. 13 Translation of DNA for Making Cellular Proteins Translation of mRNA – Actual building of new proteins by the ribosome – tRNA brings a specific AA to the ribosome, which matches the mRNA template and adds the AA to a growing peptide chain Amino acid tRNAs Rough ER Peptide bond Met …….. Cys U AC A CA A U G U GU Tyr Phe Gln A UA AAA GUU U AU U UU C AA mRNA at ribosome Initiator codon Ribosome Direction of ribosome movement Base pairing of mRNA is always A with U and G with C. A, adenine; C, cytosine; Cys, cysteine; ER, endoplasmic reticulum; G, guanine; Gln, glutamine; Met, methionine; Phe, phenylalanine; Tyr, tyrosine; U, uracil. Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002. 14 Protein Turnover There is a constant flux between making new muscle protein and breaking down old muscle protein – Known as “protein turnover” Goal for increasing muscle size is for muscle protein synthesis to exceed breakdown Muscle protein Muscle breakdown Muscle synthesis Amino acids Blood Phillips SM, et al. J Am Coll Nutr. 2009;28(4):343-354. Amino acids 15 Fast- Versus Slow-Digested Proteins in Protein Turnover In general, milk proteins are superior to soy for stimulating protein synthesis – Whey (fast protein) stimulates protein synthesis to a greater extent than casein (slow protein) and soy (moderate-fast protein) – Casein reduces muscle protein breakdown better than whey protein Mixed protein sources provide benefits of all Phillips SM, et al. J Am Coll Nutr. 2009;28(4):343-354. 16 Branched Chain Amino Acids (BCAAs) BCAAs are H3C CH-CH2- C H3C CH2 H COO- NH3+ Leucine H CH2 CH- C CH3 H COO- NH3+ Isoleucine H3C H3C CH- C COO- NH3+ Valine Unlike other amino acids, most BCAA metabolism occurs in skeletal muscle – Liver lacks first 2 enzymes in the pathway that break down BCAAs Leucine is also unique among AAs in its ability to stimulate synthesis of new muscle proteins Tom A, et al. J Nutr. 2006;136(suppl 1): 324S-330S. 17 BCAAs and β-hydroxy-β-methylbutyrate (HMB) What is HMB? – Derived from breakdown of leucine – Hypothesized to inhibit muscle protein breakdown and increase muscle synthesis, especially in combination with resistance training – Some evidence in humans that doses of 3 g/day may be effective • Additive benefits with creatine – Some studies suggest that HMB may provide greater benefit to untrained people who start weight training compared with previously conditioned athletes Nemet D, et al. Isr Med Assoc J. 2005;7(5):328-332. Nissen S, et al. J Appl Physiol. 1996;81(5):2095-2104. 18 Protein Quality Complete protein – Contains all the essential AAs in amounts that meet or exceed the amounts needed by humans • Animal proteins (except gelatin) • Soy protein Incomplete protein – Too low in one or more of the essential AAs to support human growth and development • Cannot serve as a sole source of protein in the diet • Most plant proteins are incomplete proteins (except soy) McDonald L, et al. The Protein Book: A Complete Guide for the Coach and Athlete. 1st ed. Salt Lake City, UT: Lyle McDonald Publishing; 2007. 19 Protein Quality (cont’d) Complementary proteins – Combinations of incomplete proteins that, when added together, result in a complete protein • Legumes: methionine, lysine • Grains: methionine, lysine • Example: rice and beans – Usually, combining a complete protein with an incomplete protein is considered complementary • Exception is milk and legumes – Although milk has a greater amount of sulfur-containing AAs (eg, methionine and cysteine) per gram compared with legumes, • Not enough sulfur-containing AAs are present for an ideal AA profile when the 2 foods are consumed together – Combining complementary proteins at each meal for vegetarians is not necessary • What matters is total intake of complementary proteins spread over the course of the day McDonald L. The Protein Book: A Complete Guide for the Coach and Athlete. 1st ed. Salt Lake City, UT: Lyle McDonald Publishing; 2007. Gropper SS, et al. Advanced Nutrition and Human Metabolism. 5th ed. Belmont, CA: Wadsworth Publishing; 2009:237. 20 Determining Protein Recommendations for Athletes 21 Protein Requirements Current RDA for protein is 0.8 g/kg body weight per day – ~65 g/day for a 180-lb (82-kg) individual – ~47 g/day for a 130-lb (59-kg) individual The RDA for protein is set to prevent deficiency (ie, maintain protein balance) in healthy adults Does not consider potential benefits that might be obtained from amounts beyond RDA – For example, the optimal protein intake for muscle function and athletic performance Most Americans appear to consume adequate protein by this definition USDA National Agricultural Library Food and Nutrition Information Center. Available at: http://fnic.nal.usda.gov/nal_display/index.php?info_center=4&tax_level=3&tax_subject=256&topic_id=1342&level3_id=5140. 22 Protein Intake Recommendations American College of Sports Medicine (ACSM) / American Dietetic Association (ADA) – Endurance athletes, 1.2 to 1.4 g/kg per day • Accounts for greater use of protein as fuel for energy – Strength athletes, 1.2 to 1.7 g/kg per day • To support muscle growth, particularly during early training phase when gains are greatest and protein utilization is less efficient Clinical studies suggest there is no apparent benefit at intakes above 2.0 g/kg per day American Dietetic Association, et al. Med Sci Sports Exerc. 2009;41(3):709-731. Tarnopolsky MA, et al. J Appl Physiol. 1992;73(5):1986-1995. 23 Vegetarian Diets Most vegetarian athletes meet the RDA for protein of 0.8 g/kg per day – Protein quality of non-animal / non-dairy sources is lower ACSM/ADA recommends 1.3 to 1.8 g/kg per day for vegetarian athletes American Dietetic Association, et al. Med Sci Sports Exerc. 2009;41(3):709-731. 24 How Much Protein Are Athletes Eating? Many athletes may already meet or exceed protein recommendations – Definition of “high protein” can be the absolute amount of protein, % of total energy (calories), or protein ingested per kg of body weight Strength athletes in particular may believe that much higher protein intakes are needed for muscle building – Intakes at 4- to 6-g/kg range are not uncommon – Unlikely to provide benefit beyond 2.0 g/kg – It is possible that this much protein intake could adversely affect the nutrient quality of the overall diet Protein intake below 2 g/kg per day is safe in healthy individuals Protein intake above 2 g/kg per day is not recommended due to lack of proven benefit and potential for adverse health effects Tipton KD. Proc Nutr Soc. 2011;70(2):205-214. 25 Potential Downside to “High-Protein” Diets Hydration status – Nitrogen that is obtained from consuming protein must be excreted in the urine as urea – Increased urinary output due to high protein load may increase chances of dehydration Diets very high in protein may lack appropriate amounts of carbohydrate, fiber, and some vitamins/minerals – Could impair exercise performance – Could increase long-term risk of diseases such as colon cancer • Possibly due to lack of fiber or increased intake of red meat Excessively fatty protein sources could increase risk of cardiovascular disease – Choose mostly lean protein sources • For example, salmon is more desirable than a ribeye steak Tipton KD. Proc Nutr Soc. 2011;70(2):205-214. 26 Potential Downside to “High-Protein” Diets (cont’d) Kidney disease – No good evidence of damage in individuals with healthy kidneys – Protein-rich diets are high in phosphorus, which can be harmful to individuals with kidney disease • Primarily a concern with elderly or sick individuals, as opposed to healthy athletes Bone health – Higher protein diets may increase calcium loss in urine • However, gut absorption of calcium is likely improved, so there may be no net difference – Elevated protein diets appear to have either no or a slightly beneficial effect on skeletal health Tipton KD. Proc Nutr Soc. 2011;70(2):205-214. 27 Summary of Protein Recommendations Daily Recommended Intake is 0.8 g/kg per day (2002) – No recommendation for increase in athletes American College of Sports Medicine – Strength athletes: 1.2 to 1.7 g/kg per day – Endurance: 1.2 to 1.4 g/kg per day Vegetarians may have higher dietary supplementation protein needs than omnivores Protein intakes up to 2.0 g/kg per day are generally safe in healthy adults and may be beneficial – Many athletes may already unconsciously eat this amount of protein Few convincing data show that > 2 g/kg per day is helpful – May actually increase risk of adverse events 28 What About Amino Acid Supplements? As long as the complete protein requirements are met, the individual AA requirements will be met as well – No need for additional AA supplements to prevent deficiency Because vegetarians eat few complete sources of protein, they should be cognizant of complementary protein sources throughout the day to prevent deficiency of particular AAs Branched chain amino acids are popular as a supplement among athletes – Claims mainly center on decreasing muscle soreness and improving either performance or recovery from exercise – Doses can range from 2 to 7 g/day to more than 20 g/day There are potential risks associated with AA supplements – Large doses of single AAs can prevent the absorption of other AAs, which may lead to diarrhea – Can indirectly cause deficiency of other AAs as a result American Dietetic Association, et al. Med Sci Sports Exerc. 2009;41(3):709-731. Sharp CPM, et al. J Strength Cond Res. 2010;24(4):1125-1130. Jackman SR, et al. Med Sci Sports Exerc. 2010;42(5):962-970. Harper AE, et al. Physiol Rev. 1970;50(3):428-558. 29 Example: Quantity of Amino Acids in Food 1 cup of low-fat cottage cheese (2%) has 31 g of protein – Translates to 31,000 mg of AAs – The branched chain amino acid content of the cottage cheese (leucine + isoleucine + valine) is 6,942 mg (6.9 g) Whole protein sources are best (may be less expensive) Pennington JAT. Bowes and Church’s Food Values of Portions Commonly Used. 17th ed. Philadelphia PA: Lippincott Williams & Wilkins; 1998:30,318. 30 Is Protein Used for Energy in Athletes? In general, the body prefers to spare its own protein stores from use for energy production – Skeletal muscle, in particular, will be protected in order to allow crucial fight or flight response – Only in conditions of starvation or extreme energy requirements (eg, ultramarathons) will the body break down muscle for energy However, dietary protein is commonly used as a fuel source in certain situations (eg, during endurance exercise, which can deplete carbohydrate stores in muscle) – 6 of the 20 amino acids can be metabolized for energy in resting muscle (frequent during exercise) Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002. Wagenmakers AJ. Exerc Sport Sci Rev. 1998;26:287-314. 31 Timing of Ingestion and Macronutrient Content of Meals There is increasing agreement that immediate post-exercise ingestion of protein and/or carbohydrate has beneficial effects on – Muscle glycogen replenishment (particularly carbohydrate) – Muscle protein synthesis (particularly protein) A combination of both protein and carbohydrate seems to work better than either carbohydrate or protein alone – Proportions of carbohydrate/protein vary based on individual needs • Endurance athletes prioritize carbohydrate intake for glycogen replenishment • Bodybuilders prioritize protein intake for muscle growth Zawadzki KM, et al. J Appl Physiol. 1992;72(5):1854-1859. Ivy JL, et al. J Appl Physiol. 2002;93(4):1337-1344. 32 Putting a Meal Plan Together Example: 70-kg athlete requiring 4,000 kcal/day who is exercising 120 min/day, 4 to 6 times/week Macronutrient target recommendations – Grams/kg body weight/day • Carbohydrate 7-10 g/kg (490-700 g/day) • Protein 1.5-2.0 g/kg (105-140 g/day) • Fat Typically use percentage of energy – Percentage of energy • Carbohydrate 55-65% of energy (550-650 g/day) • Protein 10-15% of energy (100-150 g/day) • Fat 20-30% of energy (88-133 g/day) Target recommendations for this athlete − Carbohydrate 600 g/day (60% of energy) − Protein 130 g/day (13% of energy) − Fat 120 g/day (27% of energy) 33 A Potential Distribution of Macronutrients Over the Course of 6 Meals/Day Meal Time Carbohydrate, g Protein, g Fat, g Breakfast 7:00 AM 90 15 15 Mid-morning snack 10:00 AM 25 10 5 Noon 75 20 20 Pre-exercise meal 1:30 - 2:00 PM 90 10 5 During exercise 3:00 - 5:00 PM 100 0 0 Post-exercise meal 5:00 PM 75 30 25 Dinner 6:30 PM 120 30 35 Evening snack 9:00 PM 25 15 15 600 130 120 Lunch TOTALS 34 Protein Content of Various Foods 1 egg, 2 egg whites, or 1/4 cup egg substitute 1 cup of milk ¼ cup cottage cheese 1 cup of yogurt 1 oz. of chicken, fish, pork, or beefa 1 oz. of cheese (except cream cheese) 1 slice of bread or ½ bagel 1 cup of cereal 2 tablespoons peanut butter 1/2 to 2/3 cup of dried beans or lentils 1 cup miso 4 oz. raw, firm tofu ½ cup peas or corn ½ cup of non-starchy vegetables 8 oz. soy milk Protein drinks and powders/serving a3-ounce Protein Content, g 6-7 8-10 7 8-13 7 7 3 3-6 7 8 8 9 3 2 5-6 10-45 portion (21 g protein) is the size of a deck of cards. Pennington JAT. Bowes and Church’s Food Values of Portions Commonly Used. 17th ed. Philadelphia PA: Lippincott Williams & Wilkins; 1998. 35 Summary Adequate protein intake is critical for athletic performance and good health For most athletes, protein intakes of 1.5 to 1.8 g/kg/day (0.68-0.81 g/lb/day) will meet protein requirements High-quality protein sources (eg, dairy products, meats, fish, chicken, soy, eggs) should be included in the diet Eating a combination of carbohydrate and protein soon after exercise can help with muscle recovery and muscle building There are potential disadvantages to excessive protein intake above 2 g/kg/day – In general, no additional benefit for strength or muscle building – Increased water loss from the body that may lead to dehydration – High-protein intake may replace carbohydrates and other vital nutrients for athletic performance and good health • Decreased overall diet quality 36