Protein and Amino Acids in Sports Nutrition

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Protein and Amino Acids in Sports Nutrition

• Rookie Module

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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.
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Functions of Proteins (contd)

• 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.
4
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.
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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

Berg JM, et al. Biochemistry. 5th ed. New York,
NY WH Freeman Co. 2002.
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Basic Structure of an Amino Acid

• Central carbon atom (alpha carbon Ca) 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.
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R Groups for Some Amino Acids
H-
Glycine
HO-CH2-
Serine
CH3-
Alanine
Threonine
H3C
CH-
Valine
H3C
Cysteine
H3C
Leucine
CH-CH2-
H3C
Methionine
CH2
CH2
Isoleucine
Aspartic acid
CH-
-OOC-CH2-
CH3
Berg JM, et al. Biochemistry. 5th ed. New York,
NY WH Freeman Co. 2002.
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Protein Digestion and Absorption
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Protein Digestion
Gastric phase (stomach)

• Hydrochloric acid (HCl) from cells in stomach
  unfolds protein

HCl

• Pepsinogen (chief cells)

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

Berg JM, et al. Biochemistry. 5th ed. New York,
NY WH Freeman Co. 2002.
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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 blood

Transporters
Berg JM, et al. Biochemistry. 5th ed. New York,
NY WH Freeman Co. 2002.
11
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. 199794(26)14930-14935. Ross
i AL, et al. J Nutraceuticals, Functional and
Medical Foods. 20003(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

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.
14
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

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.
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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

Muscleprotein
Musclebreakdown
Musclesynthesis
Aminoacids
Phillips SM, et al. J Am Coll Nutr.
200928(4)343-354.
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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.
200928(4)343-354.
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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

CH2
H3C
CH2
H3C
CH-
CH-CH2-
CH-
H3C
H3C
CH3
Leucine
Isoleucine
Valine
Tom A, et al. J Nutr. 2006136(suppl 1)
324S-330S.
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BCAAs and ß-hydroxy-ß-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.
20057(5)328-332. Nissen S, et al. J Appl
Physiol. 199681(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.
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Protein Quality (contd)

• 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 2009237.
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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?inf
o_center4tax_level3tax_subject256topic_id13
42level3_id5140.
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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. 200941(3)709-731. Tarnopolsky MA,
et al. J Appl Physiol. 199273(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. 200941(3)709-731.
25
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. 201170(2)205-214.
26
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. 201170(2)205-214.
27
Potential Downside to High-Protein Diets
(contd)

• 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. 201170(2)205-214.
28
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 gt 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. 200941(3)709-731.Sharp CPM, et
al. J Strength Cond Res. 201024(4)1125-1130.Jac
kman SR, et al. Med Sci Sports Exerc.
201042(5)962-970. Harper AE, et al. Physiol
Rev. 197050(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)

Pennington JAT. Bowes and Churchs Food Values of
Portions Commonly Used. 17th ed. Philadelphia PA
Lippincott Williams Wilkins 199830,318.
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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. 199826287-314.
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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.
199272(5)1854-1859. Ivy JL, et al. J Appl
Physiol. 200293(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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Protein Content of Various Foods
Pennington JAT. Bowes and Churchs Food Values of
Portions Commonly Used. 17th ed. Philadelphia PA
Lippincott Williams Wilkins 1998.
36
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