Protein and Amino Acids in Sports Nutrition Rookie Module 1.

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

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

Leucine Tryptophan MethionineIsoleucine Threonine LysineValine Histidine Phenylalanine


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


+

–

R Groups for Some Amino Acids

H-

CH3-

H3C

H3CCH-

H3C

H3CCH-CH2-

CH2

CH2

CH-

CH3

Glycine

Alanine

Valine

Leucine

Isoleucine

HO-CH2- Serine

Threonine

Cysteine

Methionine

Aspartic acid

CH3-CH-

OH

CH2-

SH

CH2-CH2-

S-CH3

-OOC-CH2-


Protein Digestion and Absorption

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Protein Digestion

Gastric phase (stomach) Hydrochloric acid (HCl) from cells in stomach unfolds protein

Pepsinogen (chief cells)HCl

Pepsin (enzyme)

Pepsin digests proteins 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


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

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 bloodBerg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.

Lumen

Amino acids

Oligopeptides TripeptidesDipeptides

Intestinal cell Blood

Cellular membrane

Peptidases

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Transporters

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.

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Nutrition and Cellular Synthesis of Protein

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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

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.

Nucleus

DNA

mRNA

Rough ER

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Translation of DNA for Making Cellular Proteins

mRNA at ribosome

A U G

U A C

MettRNAs

Rough ER

Initiator codon

U G U

A C A

Cys……..

Peptide bond

U A U

A U A

Tyr

Ribosome

Direction of ribosome movement

U U U C A A

A A A G U U

Phe GlnAmino acid

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

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.


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

Phillips SM, et al. J Am Coll Nutr. 2009;28(4):343-354.

MuscleMusclesynthesissynthesis

MuscleMuscleproteinprotein

MuscleMusclebreakdownbreakdown

AminoAminoacidsacids

Amino acidsAmino acidsBlood

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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

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

H3C

H3CCH-

H3C

H3CCH-CH2-

CH2

CH2

CH-

CH3

C COO-

NH3+

H

C COO-

NH3+

H

C COO-

NH3+

H

Tom A, et al. J Nutr. 2006;136(suppl 1): 324S-330S.

Leucine Isoleucine Valine

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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.

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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.

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Determining Protein Recommendationsfor Athletes

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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.

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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.

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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


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


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

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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.

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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)

30Pennington JAT. Bowes and Church’s Food Values of Portions Commonly Used. 17th ed. Philadelphia PA: Lippincott Williams & Wilkins; 1998:30,318.

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.

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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.

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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)

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A Potential Distribution of Macronutrients Over the Course of 6 Meals/Day

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Meal Time Carbohydrate, g Protein, g Fat, g

Breakfast 7:00 AM 90 15 15

Mid-morning snack 10:00 AM 25 10 5

Lunch 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

TOTALS 600 130 120

Protein Content of Various Foods

Pennington JAT. Bowes and Church’s Food Values of Portions Commonly Used. 17th ed. Philadelphia PA: Lippincott Williams & Wilkins; 1998.

Protein Content, g1 egg, 2 egg whites, or 1/4 cup egg substitute 6-71 cup of milk 8-10¼ cup cottage cheese 71 cup of yogurt 8-131 oz. of chicken, fish, pork, or beefa 71 oz. of cheese (except cream cheese) 71 slice of bread or ½ bagel 31 cup of cereal 3-62 tablespoons peanut butter 71/2 to 2/3 cup of dried beans or lentils 81 cup miso 84 oz. raw, firm tofu 9½ cup peas or corn 3½ cup of non-starchy vegetables 28 oz. soy milk 5-6Protein drinks and powders/serving 10-45a3-ounce portion (21 g protein) is the size of a deck of cards.

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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

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Protein and Amino Acids in Sports Nutrition Rookie Module 1.

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