Protein is made up of amino acids and is an important macronutrient that provides structural support and energy. There are essential and non-essential amino acids. Animal proteins contain all essential amino acids and are considered complete, while plant proteins may be lacking in one or more essential amino acids. Athletes need more protein than non-athletes to support muscle growth and recovery. Creatine and protein supplements may help increase muscle mass and strength in resistance-trained individuals, while protein likely does not improve aerobic endurance. Branched chain amino acids and glutamine supplements do not appear to provide performance benefits. Creatine can improve high-intensity exercise performance.

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Chapter 6
Protein

2. What is protein?
• Protein is a complex structure containing carbon,
hydrogen, oxygen, and nitrogen, and in some cases
sulfur. These elements combine to form amino acids.

3. Formation of peptides and protein

4. Amino Acids
Two types:
1) Essential (9)
• Must be obtained from foods in the diet
2) Nonessential (11)
• May be formed in the body

6. Animal vs. Plant Protein
• Complete proteins
– Contain adequate amounts of all 9 essential AA
– Are found in animal foods
– Contains a higher concentration of protein
• Incomplete proteins
– Limiting AA: A deficiency of one or more essential AA
• Legumes (methionine) Grains (Lysine)
– Plant foods are incomplete proteins
– Contains a smaller concentration of protein

7. What are some common foods that are
good sources of protein?
• The Food Groups
– High
• Meat and meat substitutes (legumes)
• Milk
– Lower
• Starch
• Vegetable
• Fruit
• Fat

8. Figure 6.4

10. How much protein do I need?
• Humans need enough protein to provide adequate
amounts of nitrogen and essential amino acids
• Recommended Dietary Allowance (RDA)
– Based on age and body weight
• Acceptable Macronutrient Distribution Range (AMDR)
– Based on percentage of daily energy/calorie intake

11. Protein RDA

12. Protein RDA and AMDR
• Adult RDA is 0.8 g pro/kg body Wt
• Protein AMDR is 10-35% of daily energy intake
Example - Female, 135 lbs (60 kg), eating 2,000 cal/d
• RDA is 48 grams of protein (60 x 0.8)
• AMDR of 10% provides 50 grams of protein
– 2,000 x 0.10 = 200 protein Calories
– 200/4 Calories per gram of protein = 50 grams of protein
AMDR of 35% provides 175 grams of protein

13. Summary of protein functions in the
human body
• Structural
• Transport
• Enzyme
• Hormone and neurotransmitter
• Immune
• Acid-base balance
• Fluid balance
• Energy
• Movement

16. Dietary protein needs:
Strength-Type Athletes
• Additional protein is often recommended to
help support or promote increases in muscle
tissue

17. Dietary protein needs:
Endurance-Type Athletes
• Need to recognize that carbohydrate is the
main fuel for endurance-type athletes
• More dietary protein is recommended to
– Restore protein used for energy
– Promote synthesis of oxidative enzymes and
mitochondria
– Help prevent sports anemia

18. What are some general recommendations
relative to protein intake for athletes?
1. Obtain the RDA for protein
– All athletes should obtain at least their RDA for
protein
– About 0.95 to 0.85 g/kg for young athletes
– About 0.80 g/kg for adult athletes

19. Recommendations for protein intake in athletes
2. Increase the protein RDA by 50 to 100 %
– Will increase an adult’s protein intake to 1.2 to 1.6
grams/kg body weight, and a young athlete to
about 1.7 to 1.9 grams/kg body weight
– These values are within the AMDR of 10-35% of
daily energy intake

20. Recommendations for protein intake in athletes
3. Obtain about 15 percent or more of daily energy
intake from protein
– Some athletes may need more protein than
others
• Athletes in weight-control sports
• Female endurance athletes with low energy intake
– Protein intake is within the AMDR

21. Protein intake in a wrestler
• College wrestler of 132 pounds (60 kg)
• RDA is 48 grams of protein/day
• Diet of 1,600 Calories to maintain body weight
• A diet with 12% protein will provide the RDA
– 0.12 x 1,600 = 192 Calories; 192/4 = 48 g of protein
• A diet with 20% protein will provide about 1.7 grams
of protein/kg body weight, which is near the
recommendation for strength athletes
– 0.20 x 1,600 = 320 Calories; 320/4 = 80 g of protein
– 80/48 = 1.66 grams of protein/kg

22. Recommendations for protein intake in athletes
4. Consume protein, preferably with carbohydrate,
before and after workouts: The concept of Nutrient
Timing.
– There appears to be little difference in anabolic
responses if protein is consumed either before or
after exercise
– The protein source should contain all essential
amino acids
• About 0.1 gram per kg body weight is recommended
• 7 grams for a 70-kg individual

23. Recommendations for protein intake in athletes
– Consuming carbohydrate with the protein may
also enhance the anabolic effects after exercise,
possibly attributed to increase insulin secretion
– Whole foods, such as a turkey breast sandwich,
appear to be as effective as amino acid solutions
– The carbohydrate: protein ratio should be about
3:1 or 4:1
• Commercial products such as Endurox
• Chocolate milk

24. Recommendations for protein intake in athletes
5. Be prudent regarding protein intake.
– There is insufficient evidence that increased protein intake
will enhance exercise performance
– Experts contend that given sufficient energy intake, lean
muscle mass may be maintained within a wide range of
protein intakes
– There is a metabolic rationale for increasing protein intake
if muscle hypertrophy is the goal, but the intake need not
be excessive and may be within the AMDR of 10-35% of
daily energy intake

26. Protein: Ergogenic Aspects
• Three of the top 5 most popular sport supplements
– Protein
– Amino acids
– Creatine

27. What types of protein supplements are
marketed to physically active individuals?
• Variety of products, but the protein source is usually
natural protein from milk, eggs, or soy
– Special high protein foods or diets
– Commercial liquid meals such as Nutrament
– Sports drinks and shakes; sports bars
• Whey and colostrum
– Whey protein isolates from cheese-making process
– Colostrum is first milk form cows (Theory: IGF-1)
• Other protein sources
• Protein/carbohydrate solutions

29. Do high-protein diets or protein supplements
increase muscle mass and strength in
resistance-trained individuals?
• High-protein diets
– Research data are equivocal, but suggest additional
protein may increase lean body mass but has no effect
on measures of strength
– Consuming protein after strenuous resistance exercise
may enhance muscle repair

30. Do high-protein diets or protein supplements
increase muscle mass and strength in
resistance-trained individuals?
• Whey
– Research findings are mixed, but in general show positive
effects of whey protein supplementation, about 1.2-1.5
grams per kg body weight daily, on lean body mass and
muscular strength. In one study, soy protein was also
effective.
• Colostrum
– Several studies suggest colostrum supplementation may
increase lean body mass, but effects on strength are mixed
• Additional research is recommended to evaluate the
ergogenic potential of whey and colostrum

31. Do high-protein diets or protein supplements
improve aerobic endurance performance in
endurance-trained individuals?
• High-protein diets or meals
– The Zone Diet (40:30:30), a high-protein diet, has been
advocated for endurance athletes
– Studies do not support an ergogenic effect of high-protein
diets on aerobic endurance
– Several studies suggest that a Zone Diet eating plan over
the course of a week may actually impair aerobic
endurance performance, particularly if protein replaces
carbohydrate in the diet

32. High-protein diets and aerobic endurance:
Protein/Carbohydrate Preparations
• Effects on aerobic endurance performance
– Early studies have shown increased endurance with
protein/carbohydrate versus carbohydrate alone;
however, the protein/carbohydrate solutions contained
more energy
– More recent studies balanced the energy content of both
solutions and report no difference between the two

33. High-protein diets and aerobic endurance:
Protein/Carbohydrate Preparations
• Effects on recovery from exercise
– Recent studies find that when energy content is balanced,
protein/carbohydrate solutions provide no advantage over
carbohydrate alone on subsequent exercise performance
– Some data suggest protein/carbohydrate solutions may
prevent muscle soreness, while other research does not

34. Arginine, Lysine, and Ornithine
• Theory
– Infusion of these amino acids may increase human growth
hormone (HGH); may increase IGF-1
• Main research findings:
– Arginine may decrease HGH response to exercise
– Early, poorly controlled research found ergogenic effects
– More recent well controlled studies report
• No significant increases in HGH
• No favorable changes in body composition
• No increases in strength

35. Tryptophan
• Theory
– Needed to form serotonin, a neurotransmitter in the
brain, which has been theorized to decrease pain
perception and delay fatigue during exercise
• Main research findings:
– Findings from studies are somewhat equivocal, but in
general suggest that tryptophan supplementation is not an
effective ergogenic aid for either strength or aerobic
endurance exercise

36. Branched Chain Amino Acids (BCAA)
• Leucine, isoleucine, and valine are three major amino
acids in muscle tissue
• Theoretical ergogenic mechanisms:
– Use as a fuel during exercise and spare muscle glycogen
– Decrease the rate of muscle tissue degradation
– Prevent adverse changes in brain neurotransmitter
function

37. BCAA and the Central Fatigue Hypothesis
• Main research findings:
– Some human research suggests increases in serotonin may
be associated with fatigue, but other neurotransmitters,
like dopamine, are also involved
– BCAA supplementation may be used for energy and may
help maintain serum BCAA levels

38. BCAA and the Central Fatigue Hypothesis
• Main research findings:
– Mental performance: Results of field studies are equivocal,
but several have found enhanced mental alertness in
prolonged sport events, such as tennis and soccer
– Perceived exertion: Results of laboratory studies involving
intense endurance exercise are equivocal.

39. BCAA and the Central Fatigue Hypothesis
• Main research findings:
– Physical performance with acute supplementation
• Study with 193 marathon runners suggested improved
performance in slower runners (3:05-3:30) but not faster runners
(<3:05) when consuming 7-12 grams during running
• Suggested slower runners may have depleted muscle glycogen
earlier and thus benefited more from supplementation
• Criticism of the study
– Unorthodox statistical procedure

40. BCAA supplementation
• Additional research findings:
– BCAA supplementation not necessary if
carbohydrate is available
• Carbohydrate is the best fuel for endurance athletes
• Carbohydrate helps attenuate decreases in fTRP:BCAA
– BCAA supplementation may be an effective
protocol for athletes in weight-control sports who
are on a diet
– Research is needed to help clarify the role of BCAA
supplements, or protein in general, on muscle
tissue recovery following strenuous exercise

41. Glutamine Supplementation and Endurance
Performance
• Theory
– May promote muscle growth
• Stimulate HGH
• Increase cell volume
– May stimulate glycogen synthesis
• Glutamine is gluconeogenic
– Major fuel for key cells in the immune system
• Prevent infections associated with overtraining

42. Glutamine Supplementation and Endurance
Performance
• Main research findings
– Recent studies and reviews indicate that
glutamine supplementation will increase plasma
glutamine levels but will not
• Increase muscle mass or strength
• Provide any advantage over adequate carbohydrate on
muscle glycogen levels
• Prevent the effects of overtraining
• Decrease the frequency of respiratory infections

43. Aspartates
• Theory
– Potassium and magnesium aspartates hypothesized to
• Spare muscle glycogen
• Reduce accumulation of ammonia
• Improve psychological motivation
• Main research findings
– Studies are equivocal, finding
• Either increased or decreased ammonia levels
• Laboratory cycling tests to exhaustion
– Additional research recommended: Dosage may be a
factor

44. Glycine
• Theory
– Glycine is used in the formation of creatine
• Main research findings
– Contemporary research reveals no ergogenic effect of
glycine supplementation
– Glycine is part of a multicomponent supplement
containing arginine and alpha-ketoisocaproic acid that has
been found to enhance sprint power in one study.
Additional research is needed for confirmation.

45. Glucosamine and Chondroitin
• Dietary supplements
– Glucosamine derived from shellfish; chondroitin from cattle cartilage
• Theory
– Glucosamine helps form the structural basis of cartilage
(proteoglycans), and chondroitin helps provide resiliency
– May help prevent joint pain associated with exercise training

46. Glucosamine and Chondroitin
• Research findings
– Limited research with highly trained individuals; most are
with older, arthritic individuals
– A substantial number of studies and reviews indicate
supplementation reduced joint pain and improved
mobility
– Large NIH study (GAIT) found no overall reduction in knee
pain in osteoarthritic individuals, but the supplement did
provide relief to a subset of individuals with moderate to
severe knee pain

47. Glucosamine and Chondroitin
• Research findings
– Beneficial effects were minimal in two studies with
younger, physically active males
– Glucosamine sulfate appears to be the most effective
form; chondroitin is not effective

48. Glucosamine and Chondroitin
• Precautions and recommendations for use
– Considered safe, but may cause bloating and diarrhea
– Consult with your physician as there may be
complications, such as with blood glucose control in
diabetics
– Reasonable dose would be 1,500 mg of glucosamine and
1,200 mg of chondroitin for 2-4 months. If pain symptoms
have not improved, they probably are not going to.

49. Creatine
• Creatine is found naturally in animal foods,
especially meat
• Creatine may also be synthesized by the liver
and kidney
Food g/Kg
Milk 0.1
Tuna 4.0
Salmon 4.5
Beef 4.5
Pork 5.0

50. Creatine
• Discovered 1927
• Synthesized in 1990s as
a dietary supplement
• Research as an
ergogenic aid
progressed rapidly

51. Creatine Supplementation
• Theory
– May increase muscle levels of PCr
– May increase performance in very high intensity
exercise
– May enhance performance in prolonged
endurance events which incorporate short sprints
– May enhance interval training

52. Loading phase
Fast protocol: 20-30 grams/day for 5-7 days
Slow protocol: 3 grams/day for 30 days
Maintenance phase
2-5 grams/day
Recommended Protocol
Creatine Supplementation
(20g/day for 5 days) with and
without Carbohydrate (360g)
Adapted from Green, A., et al. ACTA Physiol Scand, 1996.

53. Creatine Supplementation
• In general, research findings also indicate that creatine
supplementation may enhance performance in very high-
intensity exercise tasks, such as the 100-meter sprint in track
and sprint cycling

54. Creatine Supplementation
• Of seven recent well-controlled studies using a standard
creatine-loading protocol and evaluating the effect on single
or repetitive sprint-run or sprint-cycle performance ranging
from 5 to 100 meters, creatine supplementation improved
performance in five of the trials, but had no effect in the
other two.
• For example, one study reported significant improvements in
male sprinters in 100-meter sprint velocity and time to
complete six intermittent 60-meter sprints.
• A meta-analysis of 57 studies revealed an effect size of 0.24
favoring creatine over the placebo treatment

55. Creatine Supplementation:
Effect on body mass
• In general, research indicates increases in body mass, mainly
as muscle tissue, in both males and females, including both
trained and untrained
• Studies report increases in myosin and myonuclei
concentration

56. Creatine supplementation: Safety
• Kidney and liver function
– Consuming recommended dose does not appear to
increase health risks
– Those with liver or kidney disease may be at risk
• Gastrointestinal distress
– Large doses may cause nausea, vomiting and diarrhea
• Dehydration, muscle cramps and tears
– Appears to cause few problems with exercise in the heat
– Possibility of anterior compartment syndrome
• Overdoses and contaminants
– Creatine appears to be safe at 5 grams per day
– Some products may contain contaminants, like ephedrine

57. Creatine supplementation:
Medical applications
• Increased strength in some conditions
– Muscular dystrophy
– Patients with heart disease
– Injury to the spinal cord
• Facilitate rehabilitation from musculoskeletal injury
• Reduce the loss of muscle mass (sarcopenia) with
aging

58. Beta-Hydroxy-Beta-Methylbutyrate
(HMB)
• Theory
– Beta-hydroxy-beta-methylbutyrate (HMB), a by-product of
leucine metabolism, is theorized to inhibit the breakdown
of muscle tissue during strenuous exercise

59. Beta-Hydroxy-Beta-Methylbutyrate
(HMB)
• Main research findings with strength-trained athletes
– Overall, research findings are equivocal regarding the
ergogenic effect of HMB supplementation on muscle mass
and strength in untrained individual
– The available data indicate that HMB supplementation
does not appear to affect muscle strength, body
composition, or anaerobic exercise performance in
resistance-trained individuals
– Research does not support any protective effects against
muscle tissue damage during resistance training

60. Beta-Hydroxy-Beta-Methylbutyrate
(HMB)
• Main research findings with endurance athletes
– One study with distance runners reported HMB
supplementation (3 g/day for 6 months) decreased
markers of muscle damage following a 20K run
– One recent study found HMB could increase VO2max
during 5 weeks of interval training in active college
students
– No studies have shown improvement in endurance
exercise performance following HMB supplementation

61. Beta-alanine and Carnosine
• Theory
– Beta-alanine may increase intramuscular stores of
carnosine, which can serve as an antioxidant or as a buffer
of hydrogen ions, reducing acidity, and increasing the
lactate threshold
– Beta-alanine may also form another peptide, anserine,
which may function as an antioxidant in muscles

62. Beta-alanine and Carnosine
• Main research findings
– Anserine supplementation increases muscle
carnosine
– Research findings are equivocal relative to
ergogenic effects on anaerobic-type exercise
performance
• Improved performance cycling @ 110% VO2max
• No effect on 400-meter run time
– No ergogenic effect on aerobic-endurance
• No effect on maximal aerobic power

63. Tyrosine
• Theory
– Tyrosine is a precursor for the catecholamine hormones
and neurotransmitters epinephrine, norepinephrine, and
dopamine; augmentation may have an ergogenic effect
• Main research findings
– Research is very limited
– No effect on aerobic endurance, anaerobic power, or
muscular strength

64. Taurine
• Theory
– Taurine is synthesized from amino acids, but is not
classified as an amino acid
– Theorized to help prevent muscle tissue damage during
exercise; may function as an antioxidant
• Main research findings
– One study has shown ↑ stroke volume during exercise
– One study reported ↑ VO2max and exercise time to
exhaustion associated with antioxidant effects
– These preliminary findings need further research

65. Inosine
• Theory
– Inosine is a nucleoside, not an amino acid
– Theorized to improve ATP production and also to improve
oxygen delivery to muscles during exercise
• Main research findings
– Well-controlled studies indicate inosine supplementation
• Does not increase VO2max or related physiological
variables
• Does not improve 3-mile treadmill run time
• Has no effect on cycling tests of the three energy
systems
• May impair anaerobic energy production

66. Does a deficiency of dietary protein
pose any health risks?
• Protein-Calorie malnutrition is a worldwide problem
– Political and economic problems
– Impaired immune functions
• The elderly may be prone to protein undernutrition
– May impair immune functions; increase infections
– May hamper optimal bone development
• Young athletes in weight-control sports
– Loss of muscle mass and hemoglobin

67. Does excessive protein intake pose any
health risks?
• Excess amounts of specific proteins may cause
allergic reactions in some individuals
• AMDR range is 10-35% of energy intake
• No UL has been established for protein intake
– High protein intake poses no health risks to most persons
– NAS indicates the source of protein may be related to
various health risks

68. Excessive protein intake and health risks
• Cardiovascular disease and cancer
– Dietary protein itself does not appear to cause CHD or
cancer
• High meat diets may be rich in saturated fats
• AICR indicates there is convincing evidence that red and processed
meats contribute to colorectal cancer
– High protein diets may actually help promote weight loss,
a preventive measure against CHD
– Soy protein in natural, whole foods may have beneficial
health effects

69. Excessive protein and health risks
• Liver and kidney function
– The liver processes ammonia and the kidneys excrete urea
and ketones, which are formed on high protein diets
– In general, high-protein diets do not have adverse effects
on individuals with normal liver and kidney functions
– Individuals prone to liver or kidney disease should use
caution with protein intake
• Chronic kidney or liver disease
• Diabetics
• Individuals prone to kidney stones

70. Excessive protein and health risks
• Bone and joint health
– Excessive protein intake may increase urine acidity, which
may increase calcium excretion
– Calcium loss is predicted to be 1 mg of calcium for an
average increase of 1 gram of dietary protein
– A diet low in calcium and high in protein may promote
bone loss
– The key is to obtain adequate calcium and protein because
both are needed in adequate amounts for bone formation

71. Excessive protein and health risks
• Heat illnesses
– The excretion of urea and ketone bodies in urine could lead
to excessive fluid losses and dehydration
– A high-protein diet could increase resting energy
expenditure
– Both of these effects could compromise temperature
regulation during exercise in the heat, which will be
discussed in chapter 9

72. Does the consumption of individual
amino acids pose any health risks?
• No UL has been established for specific AA, but the
NAS notes caution is warranted in using any single
AA in amounts greater than normally found in food
• Free AA are manufactured to serve as drugs or
dietary supplements
• Excessive amounts may cause health problems
– Interfere with absorption of other AA
– Cause gastrointestinal distress
• Sound advice is to obtain your AA through foods