Chapter 5: Proteins

Question 1

Importance of protein

Answer 1

critical to growth and development
role can be overstated if it is elevated above other nutrients
protein functions optimally only when energy intake from CHO and fat is sufficient

Question 2

Amino acid (AA)

Answer 2

basic component of proteins
contain carbon, hydrogen, oxygen, and nitrogen
20 AA’s are used by the body to make various proteins - 9 are indispensable (essential/body can’t make them); 11 are dispensable (non-essential/can be made by liver or found in food) with 6 being conditionally indispensable (during periods of stress/starvation body can’t make enough)

Question 3

Issue of protein deficiency

Answer 3

in western countries where few healthy adults are at risk for amino acid deficiencies
those at risk for low protein intake include those with eating disorders, the frail elderly, those with food insecurity, and people with liver or kidney disease

Question 4

Protein quality

Answer 4

based on the amounts and types of amino acids and the extent to which the amino acids are absorbed
measure by the digestible indispensable amino acid score

Question 5

Complete proteins

Answer 5

animal sources
contain all the indispensable amino acids in the proper amounts and proportions to each other to prevent amino acid deficiencies and to support growth

Question 6

Incomplete proteins

Answer 6

plant sources
lack one or more of the indispensable amino acids or the proper concentrations
doesn’t have all the essential amino acids

Question 7

Complementary proteins

Answer 7

combining two incomplete proteins
when consumed during the same day they can be nutritionally equal to a complete (animal) protein

Question 8

Peptide

Answer 8

two or more amino acids that are combined
dipeptide = two amino acids
tripeptide = three amino acids
polypeptide = four or more amino acids
most proteins are polypeptides and are made up of many amino acids

Question 9

Functions of protein in the body

Answer 9

1) Enzymes - necessary to catalyze (speed up) reactions; unique structure of each enzyme interacts with its substance; specific to molecule that it must interact with
2) Hormones and other regulators - hormones are compounds that act as chemical messengers to regular metabolic reactions; AA’s regulate critical metabolic pathways
3) Structural proteins - proteins of muscle and connective tissue; proteins found in skin, hair, and nails
4) Transport proteins - like delivery trucks of the body
5) Immune system proteins - immune system is protein-based; deficient in protein = decrease immune response

Question 10

Digestion

Answer 10

begins in the stomach
protein is denatured by gastric juices containing HCl which allows other enzymes to break them down further
HCl activates pepsin which is an enzyme that will breakdown the proteins into smaller unites
generally breaks down very large polypeptides into smaller units that are still quite large

Question 11

Absorption

Answer 11

takes place in the small intestine
2/3 of amino acids are absorbed in the form of dipeptides or tripeptides, and the other 1/3 are absorbed as individual amino acids
different protein carriers have affinity with certain amino acids
indispensable amino acids are absorbed more rapidly than dispensable amino acids
once absorbed, he body does not distinguish between the amino acids originally obtained from exogenous or endogenous sources
once absorbed, the majority of amino acids will remain in the liver for metabolism with a small amount circulating in the blood and being transported to other parts of the body
amino acids that are not absorbed are excreted in feces
some amino acids will not leave the small intestine cells because they will be used to make cellular proteins with those not used being released into the blood via the portal vein

Question 12

Transportation and Storage

Answer 12

after absorption, some amino acids are transported to the liver whereas others circulate in the blood
liver monitors the supply of amino acids and dictates which amino acids will be transported to which tissues (with the exception of BCAA’s due to low amounts of BCAA transferase in liver)
50-65% of amino acids found in liver with the remaining being in amino acid pool
10-25% of resting metabolism is expended each day to synthesize and degrade proteins

Question 13

Amino acid pool

Answer 13

free amino acids that are circulating in the blood or in the fluid found within or between cells
always in flux as a result of food intake, exercise, and the breaking down or building of tissues, especially skeletal muscle
constant flux known as protein turnover
consist of amino acids that are absorbed from food but do not remain in the liver
amino acids in this pool are involved in anabolic and catabolic processes

Question 14

Livers role in metabolism of protein and AA’s

Answer 14

major site for amino acid metabolism by monitoring the body’s AA needs and responds accordingly with anabolic or catabolic processes

Question 15

Anabolic

Answer 15

building complex molecules from simple ones

Question 16

Catabolic

Answer 16

breakdown of complex molecules into simple ones

Question 17

Deamination

Answer 17

comes from first removal of amino group from the amino acids
part of catabolism

Question 18

Transamination

Answer 18

comes second
transfer of the amino group to another carbon skeleton
part of both catabolism and anabolism

Question 19

Amino acid pool

Answer 19

anabolic process = synthesis of skeletal muscle protein that uses amino acids from the pool to synthesize the new proteins
catabolic process = when skeletal muscle proteins are degraded and amino acids are returned to the amino acid pool

Question 20

Anabolic functions (occurs in the liver)

Answer 20

liver enzymes (amino acids are incorporated), plasma proteins (where the remaining amino acids go), synthesis of muscle protein, albumin (protein that circulates in the blood and is made in the liver), manufacturing of compounds (ie. creatine)
many of the proteins made in the liver are synthesized and released in response to infection or injury

Question 21

Catabolic functions

Answer 21

amino acids are not stored for future use like CHO and fats, but the so-called storage site protein is skeletal muscle
in extreme circumstances, protein can be removed from skeletal muscle but the removal of a large amount of AA’s has a negative effect on muscle’s ability to function so the body tries to protect skeletal muscle from being used in this way

Question 22

Amount of energy in protein

Answer 22

protein yields about 4 kcal/g
CHO and fats are used first, then proteins last if needed
known as protein sparing effect

Question 23

Protein metabolism during exercise

Answer 23

proteolysis (muscle breakdown) occurs when the body is stressed (ie. endurance exercise) and is stimulated by cortisol
in endurance exercise as muscle glycogen stores decline substantially, the skeletal muscle uses some amino acids for energy
metabolic response is influenced by the CHO content of athlete’s diet (ie. low CHO diet and CHO depleted = oxidation of amino acids is increased and vice versa)
body prefers to use CHO when exercising, amino acids are back up energy source
3-5% of energy comes from amino acids, but during prolonged exercise that amount is higher
amino acids are also used for gluconeogenesis (convert to glucose for energy) - 18 of 20 amino acids can be converted to glucose

Question 24

Ammonia

Answer 24

by-product of the breakdown of amino acids
must be filtered out in the urine
nitrogen is also lost in urine every day

Question 25

Resistance training

Answer 25

results in muscle protein breakdown at time of exercise, but eating protein during rest and recovery is extremely important as it results in a positive protein balance

Question 26

Breakdown and building of protein

Answer 26

body is constantly doing these processes healthy adults turn over 300g of protein a day 1-2% of total protein in the body is degraded each day (mostly from skeletal muscle) 80% of amino acids are synthesized into new proteins, 20% are broken down 5g of nitrogen (30g of protein) is urinated out

Question 27

Nitrogen balance and Net protein balance

Answer 27

nitrogen balance is the difference between nitrogen intake nitrogen loss exercise temporarily brings body into nitrogen balance during growth phases want the body to be in a positive nitrogen balance overtraining and starvation diets can bring the body into a negative nitrogen balance food and recovery must include protein intake to bring the body back into a nitrogen balance protein turnover is difference between protein synthesis and protein degradation

Question 28

Labile protein reserves

Answer 28

something that is readily or frequently undergoes change found in the liver and other organs allows the body to respond to very short-term changes in protein intake allows the body to protect the skeletal muscle from being used as an amino acid source for short-term emergencies

Question 29

Short and Long-term changes in body protein

Answer 29

labile protein reserves and amino acid pool

Question 30

Starvation state

Answer 30

rate of protein synthesis is decreased by 30% or greater during starvation tissue most affect = skeletal muscle amino acids in skeletal muscle are used to protect the visceral tissues opposite of what happens under normal circumstances (ie. labile protein reserve)

Question 31

Skeletal muscle protein synthesis

Answer 31

many factors influence protein muscle synthesis and degradation - one's genetic potential for cellular protein synthesis; strongly influenced by exercise, specifically strength training strength training stimulates both protein synthesis and protein breakdown (mainly synthesis) with the greatest increase in myofibrillar proteins feeding promotes anabolic state in the muscle, particularly is the meal contains adequate amino acids and is consumed immediately or within 2 hours after exercise insulin plays roles in anabolic process by stimulating protein synthesis and acting to inhibit protein degradation

Question 32

Exercise effect on the immune system

Answer 32

moderate exercise has a positive effect on immune system athletes at risk for immunodepression = prolonged training session 90-120 minutes or more moderate to high intensity exercise strenuous bout of exercise = immune system drops for 3-24 hours athlete susceptibility to infection is multifactorial and more research is needed to isolate the influence of exercise in humans positive effects = reduction in systemic inflammation (good thing)

Question 33

Recommended protein consumption

Answer 33

dietary reference intake (DRI) for adults is 0.8 g/kg/body weight athletes should plan the type (quality), distribution, and timing of protein intake - 1.2-2.0 g/kg/day general guidelines for athletes guidelines are under the assumptions that total energy intake is adequate and the quality of protein is good range for athletes depending on exercise levels (intensity, duration, periodization) intake depends on goals for skeletal mass, muscle growth, etc. sufficiency and appropriate timing for protein intake is required older adults consume at least 1.2 g/kg/day to avoid sarcopenia when energy intake is deficient, protein intake should be minimum 1.8 g/kg/day to prevent decreased skeletal muscle mass

Question 34

Amino acid metabolism

Answer 34

involves the catabolism of amino acids which takes place in the liver during this process ammonia is produced (toxic to body) ammonia must be converted urea for excretion all humans have max rate of urea synthesis, exceptionally high intake of protein could leads to an elevated blood ammonia level (dangerous medical condition) a suggested maximum intake of protein is 2.5 g/kg/day, but healthy adults appear to be able to tolerate protein intakes as high as 3.5 g/kg/day without adverse side effects

Question 35

High-quality proteins

Answer 35

not all proteins are capable of stimulating muscle protein synthesis to the same degree those that maximize muscle protein synthesis are high-quality proteins or proteins with high biological value - found in food like milk and dairy products, meat, fish, eggs, and soy products; protein supplements can also contain high-quality proteins that are derived from whey, casein, soy, and egg proteins

Question 36

How to maximize muscle protein synthesis?

Answer 36

recommended that athletes consume 0.25-0.3 g/kg/day of protein immediately after exercise, if possible, or at least within 2 hours after exercise ends

Question 37

Timing of protein intake

Answer 37

catabolic state is followed by anabolic state, an environment that allows for recovery from the acute effects of exercise and for skeletal muscle growth first hour or two after exercise is referred to as anabolic window intake of protein after resistance exercise increases the amount of amino acids in the blood which activates signalling molecules necessary to promote muscle protein synthesis

Question 38

Protein consumption after resistance exercise

Answer 38

immediately after exercise, when possible, and preferably within 2 hours after exercise consume protein high-quality protein containing a large amount of indispensable amino acids like egg white, whey, casein, and soy ~15-25g of protein as a food, beverage, or protein supplement for maximum protein synthesis, high quality protein source containing ~1.7-2.4 g of leucine (ie. milk, dairy products, eggs, or supplements containing whey protein isolate)

Question 39

CHO-protein consumption after exercise

Answer 39

CHO consumed immediately after exercise are beneficial to restore muscle glycogen and stimulate the release of insulin which increases amino acid uptake and inhibits muscle degradation many athletes will consume beverages with both CHO and protein is most beneficial for recovery

Question 40

CHO-protein consumption during exercise

Answer 40

during resistance training there are thoughts that consuming CHO and protein can offset muscle protein breakdown and enhance muscle protein synthesis

Question 41

Protein consumption before exercise

Answer 41

insufficient evidence to suggest that protein consumption prior to exercise is beneficial for recovery

Question 42

Protein consumption before sleep

Answer 42

at least 40g of protein before sleep can help minimize muscle protein breakdown and help muscle protein synthesis especially if athlete has been resistance training for maximum muscle protein synthesis some athletes may set an alarm midway through their sleep cycle to consume a protein-containing beverage or supplement

Question 43

Athletes and protein consumption

Answer 43

majority of athletes consume sufficient protein no current evidence that high-protein diets result in renal insufficiency no evidence that high-protein diets adversely affect bone health large amounts of protein can result in dehydration because additional water is needed to metabolize protein need to watch CHO, fat and overall caloric intake those at risk for low protein involve athletes struggling with eating disorders or are restricting energy in order to keep body weight or fat level

Question 44

Energy intake effect on protein intake

Answer 44

amount of protein required is related to overall energy intake adequate energy intake from CHO or fat spares amino acids from being used for energy and helps maintain nitrogen balance adjustments to protein intake will need to be made when energy intake is deficient amount of protein needed depends on the magnitude of the energy deficit and whether it is acute or chronic higher protein diet is recommended to the athlete who is dieting as a way to protect against the loss of muscle mass

Question 45

Long-term, substantial energy deficit

Answer 45

typically result in low protein intake chronic energy deficit = more protein is needed to maintain nitrogen balance if energy and protein intake are too low theres a reduction in the synthesis of some body proteins, degradation of skeletal muscle proteins, and returns the body to a balanced state but a lower functional level net protein balance will be achieved but at the expenses of training, recovery, performance and health starvation conditions leads to changes in hormonal balances because food is not being consumed so little insulin is being produced muscle and fat cells become resistant to the insulin that is present without insulin, protein synthesis is further reduced because insulin promotes the uptake of amino acids by muscle cells hormonal status favours the breakdown of skeletal muscle protein to provide amino acids to make glucose

Question 46

Dieting and lean body mass

Answer 46

70-80% of weight lost from adipose tissue 20-30% from lean body mass, almost entirely from skeletal muscle

Question 47

Dieting recommendations for athletes

Answer 47

daily energy deficit should be moderate (~500kcal) resistance exercise must be performed daily protein intake should be at least 1.8-2.7 g/kg high quality protein sources should be consumed post exercise protein consumption = 0.25-0.3 g/kg leucine containing and whey protein sources meals or substantial snack should be distributed evenly throughout the day need adequate CHO for recovery

Question 48

"Making weight"

Answer 48

involves short term energy deficits for competing in a certain weight category substantially reduce caloric intake for a short time, goal to lose body weight through fat and water loss raises serious concerns about hydration status, the potential for heat illness, maintenance of skeletal muscle mass, ability to exercise due to depleted glycogen stores, hypoglycemia, and declines in RMR some sports have enacted regulations based on minimum weight formula to determine the appropriate weight category for each competitor

Question 49

Low protein intake and immune system

Answer 49

immune system highly dependent on protein low protein intake usually accompanies low energy intake and low nutrient intake some immune mechanisms are impaired

Question 50

Impact of injury/infection on protein status

Answer 50

injury or infection has effect on protein status increased loss of nitrogen from the body and negative nitrogen balance which is intensified if a fever is present illness typically results in lack of appetite which creates negative nitrogen balance and leads to body depending on its stores and reserves for amino acids treatment should include restoring protein status bacterial infections takes 2-3 times the duration of the infection to restore the protein that has been lost protein intake of an additional 0.2-0.3 g/kg/day during recovery period

Question 51

Protein sources

Answer 51

found in both animal and plant foods animal source includes meat, fish, poultry, eggs, milk, and milk products plant sources include beans, legumes, nuts, and seeds grains and vegetables contain smaller amounts than other protein-containing foods but are often consumed in large quantities and contribute a reasonable amount to total daily protein intake

Question 52

Vegetarian and vegan diet

Answer 52

vegetarians may consume animal products like eggs vegans do not consume any product derived from animals well-planned vegetarian diets are appropriate for all individuals emphasize protein rich vegetarian foods soy protein isolate is considered comparable in quality to animal protein can support optimal performance if the diet contains the proper quantity and quality of protein and is sufficient in calories

Question 53

Protein supplements

Answer 53

neither more or less effective than food proteins for skeletal muscle growth may be more convenient due to portability, preparation, and easy storage

Question 54

Protein supplement ingredients

Answer 54

contain whey, casein, egg, and soy proteins whey and casein come from milk whey protein concentrate and whey powder contain lactose whey protein isolate is concentrated source of protein because both the CHO and the fat are removed casein high in glutamine

Question 55

Whey

Answer 55

fast-acting protein high percentage of indispensable amino acids

Question 56

Casein

Answer 56

slow-acting protein lower amount of indispensable amino acids

Question 57

AA's supplements

Answer 57

appear to be safe at recommended doses many fall short when it comes to effectiveness complicated physiological processes cannot be affected to a large degree by a single factor

Question 58

Beta-alanine

Answer 58

effective for buffering muscle pH in athletes performing high-intensity exercise lasting 1-40 minutes

Question 59

HMB

Answer 59

not effective in resistance trained athletes small to very small increases in strength in untrained individuals emerging evidence suggests that skeletal muscle breakdown may be reduced with high intensity or prolonged endurance exercise

Question 60

BCAAs

Answer 60

not effective for improving performance little evidence for reduction of postexercise fatigue some promise for immune system support

Question 61

Glucosamine/Chondroitin sulfate

Answer 61

generally not effective for reducing joint pain or increasing functionality in those with osteoarthritis

Question 62

Glutamine

Answer 62

unlikely to be effective

Question 63

Growth Hormone releasers (arginine)

Answer 63

effective for stimulating growth hormone release not effective for increasing muscle mass or strength

Question 64

Nitric oxide (NO)/arginine alpha-ketoglutarate (AAKG)

Answer 64

may be effective at increasing performance in untrained individuals, conflicting results with athletes