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Sport nutrition (EXCI 445) > Chapter 6- Carbohydrates > Flashcards

Chapter 6- Carbohydrates Flashcards

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1
Q

what is the most important fuel for the CNS ?

A

carbs

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2
Q

to optimize carb availability, what should an athlete do?

A

carb feeding before exercise and carb feeding during exercise

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3
Q

explain the Krogh and Lindhart experiment recognizing the importance of carbs as fuel for exercise.

A

high fat diet for three days (bacon, butter, eggs) and then high carb for 3 days (potatoes, flour, bread, sugar) w 2h exercise test. exercise reported as easy on carb diet, and as inducing fatigue on fat diet.
RER also decreases on a high fat diet

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4
Q

what did Levine, Gordon, and Derick observe when they measured blood glucose in some participants in the Boston Marathon

A

most runners, glucose concentration declined markedly after the race. then, recommended carb snacks to runners in next years marathon to reduce hypoglycemia and fatigue

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5
Q

what did Dill, Edwards, and Talbott do to their dogs ?

A

didn’t feed them carbs before running, dogs were fatigued after 4-6 hrs
when they were fed carbs, ran for 17-23 hrs

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6
Q

what did Christensen show about exercise intensity and carb utilization ?

A

that with increasing intensity, the proportion of carb used increases.

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7
Q

what did muscle biopsies in the 1960s show ?

A

that high carb diets (70 percent) increased endurance capacity and muscle glycogen

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8
Q

how is glycogen measured , in what units ?

A

mmol glucosyl units (glucose) / kg dry or wet mass

dry mass determined by freeze drying muscle sample

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9
Q

muscle contains how much water ? what does that mean ?

A

75-80% water, so dry mass will be 4.5 x wet mass concentrations

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10
Q

at rest, how much muscle glycogen do we have ?

A

300-400g CHO

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11
Q

how does hepatic glucose output depend on exercise intensity?

A

the higher the intensity, the more glucose output

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12
Q

what is the main determinant of the rate at which muscle glycogen is oxidized ?

A 
exercise intensity (used a lot more at higher intensity)
at lower intensity, utilizing more acetyl coA from carb or fat
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13
Q

what is the main role of the liver ?

A

regulation of blood glucose to maintain homeostasis

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14
Q

why can’t muscle glycogen be used to regulate blood glucose ?

A

because once glucose is inside the muscle, phosphorylated by hexokinase to G6P and muscle doesn’t have the enzyme that turns it back to glucose

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15
Q

which enzyme does muscle lack which would technically turn G6P back into glucose ?

A

glucose 6 phosphatase

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16
Q

which has the higher quantity of glycogen- liver or muscle ?

A

muscle

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17
Q

which has the higher concentration of glycogen- liver or muscle ?

A

liver

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18
Q

after an overnight fat, what is the mass of liver glycogen ?

A

<20g

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19
Q

what is the weight of the liver ?

A

1.5 kg

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20
Q

what is the rate of brain glucose usage in sleep

A

0.1g/min

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21
Q

during exercise, how does the rate of glucose utilization by tissues other than muscle change ?

A

doesn’t change much

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22
Q

at rest, what is the liver output of glucose and from which sources ?

A

150 mg/min
40% from gluconeogenesis
60% from glycogenolysis

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23
Q

what is the liver output of glucose during high intensity exercise and from which sources ?

A

1000 mg/min (almost 10-fold than at rest)
<10% from gluconeogenesis
>90% glycogenolysis

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24
Q

what will be the concentration of blood glucose desired ?

A

4-4.5 mmol/L

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25
Q

when is there less gluconeogenesis ?

A

with food intake

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26
Q

when is there more gluconeogenesis ?

A

starvation, and high duration of exercise

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27
Q

what is the most important glucoregulatory hormone ?

A

insulin

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28
Q

in exercise, how does insulin concentration change ?

A

decreases

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29
Q

what are 4 hormones that promote glycogen breakdown?

A

glucagon, cortisol, epinephrine, norepinephrine

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30
Q

in exercise, there is less insulin secretion but glucose uptake by muscle still occurs, enhanced by what ?

A

muscle contraction

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31
Q

when is it considered hypoglycemia ?

A

<3 mmol/L

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32
Q

what is hypoglycemia ?

A

insufficient uptake of glucose by brain

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33
Q

what kind of breath one may have in hypoglycemia ?

A

acidosis (fruity)

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34
Q

what can happen to HR in hypoglycemia

A

increased HR

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35
Q

what kind of food do you give someone with hypoglycemia ?

A

high GI and fast absorption, like juice

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36
Q

explain in more detail what insulin does ?

A

promotes uptake and storage of glucose

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37
Q

what two enzymes does insulin regulate

A

glycogen synthase increases and glycogen phosphorylase decreases

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38
Q

what happens at about 80%Vo2MAX when it comes to the mismatch glucose uptake and production ?

A

the liver produces more glucose than is uptaken

(increased hepatic release), probably due to feedforward mechanism resulting in elevated high blood glucose

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39
Q

what happens in later stages of exercise when it comes to the mismatch of glucose uptake and production ?

A

rate of glucose production may become insufficient as glycogen is depleted

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40
Q

what does pre-exercise carb consumption induce ?

A

reactive/rebound hypoglycemia

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41
Q

what are the two reasons for reactive hypoglycemia ?

A

1) preexercise CHO feeding, with increased insulin levels and decreased glucose output
2) muscle contraction leads to GLUT4 translocate and glucose uptake, meaning less in blood

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42
Q

2 ways to reduce reactive hypoglycemia

A

low GI preexercise CHO feeding

warm up exercise

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43
Q

how will repeated running bouts influence muscle glycogen concentration if you are on a high CHO diet vs a low CHO diet

A

if you are on a low CHO diet, there will be a marked decreased and you will slowly deplete your stores

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44
Q

in what exercise type do carbs help ?

A

every type: endurance, intermittent, short-duration high-intensity

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45
Q

how will muscle glycogen relate to fatigue during an activity??

A

on a graph, it will look like an x with the two lines intersecting as muscle glycogen decreases and fatigue increases
after 1.5 hours, liver glycogen starts being converted into glucose

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46
Q

what is the crossover point ?

A

when exercise intensity increases and more carbs start being used than fats

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47
Q

with training the crossover point between carb and fats usage changes in what manner ?

A

you start sparing more glycogen and using more fats

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48
Q

SNS stimulation will promote usage of which energy source ?

A

fats

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49
Q

what are the Olympic recommendations for carb intake per day?

A

5-12g/kg bw/d

up to 10-13 g/kg bw/d if you exercise for 3+ hours daily

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50
Q

during training what kind of food intake should you have ?

A

sports drink within the first hours

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51
Q

what kind of carbs should athletes be consuming ?

A

high GI

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52
Q

why is it important to eat nutrient rich carb foods ?

A

to provide a good source of protein (promoting muscle recovery) and other things

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53
Q

for recovery, what are the recommendations for food when the period between exericse sessions are less than 8 hours?

A

athlete should begin carb intake as soon as practical after the workout, to maximize the recovery time between sessions

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54
Q

for recovery, what are the recommendations for food when the period of recovery is 24 hours or more

A

organize pattern and timing of CHO rich meals and snacks

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55
Q

what is the difference in glycogen synthesis when you ingest a solid or a liquid ?

A

no difference

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56
Q

which foods have high GI? (>85)

A

potato, pancakes, bread, cereal, watermelon, gatorade

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57
Q

which foods have moderate GI? (60-85)

A

rice, ice cream, candy bars

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58
Q

which foods have low GI? (<60)

A

honey, carrots, apples, bananas, grapes, beans

59
Q

what is GI?

A

area under curve of blood glucose over 2h after 50g of food

60
Q

how do you calculate GI?

A

AUC test food/ AUC ref food (usually white bread) x100

61
Q

what is glycemic load?

A

GI of food or meal x g available CHO in the meal / 100
meaning food affects other foods’ absorptin
the glycemic load

62
Q

what is a low, med, high GL ?

A

low: 0-10
med: 11-19
high: 20+

63
Q

what are the 6 things that may alter the glycemic index?

A 
type of CHO 
fiber content
protein and fat content
timing of meal 
other foods
total amount eaten
64
Q

how will fiber content affect GI ?

A

high fiber decreases GI

65
Q

how will protein and fat content affect GI?

A

increased protein and fat decreases GI

66
Q

how will the timing of the meal affect GI ?

A

empty stomach means there will be increased absorption

67
Q

what kind of GI for pre exercise meal ?

A

low GI

68
Q

what kind of GI during high intensity or long duration exercise

A

med-high GI

69
Q

what kind of GI after exercise ?

A

high GI

70
Q

as exercise intensity increases and muscle glycogen gets depleted, hepatic glucose output ______

A

increases

71
Q

what is the main glycogen that maintains blood glucose concentrations ?

A

liver

72
Q

as exercise intensity increases, how will the contribution of maintaining blood glucose change between glycogenolysis relative to gluconeogenesis ?

A

more glycogenolysis will happen relative to gluconeogenesis

73
Q

what are the three variables of CHO availability

A

timing, amount, GI of food

74
Q

what are the goals of carb intake 24h before training or right before ?

A

24h before: replenish muscle glycogen

right before: optimize liver stores

75
Q

describe the original supercompensation protocol ?

A

days -7 to -4 no carbs, high protein high fat followed by days -3 to competition high carb (75%)
glycogen-depleting exercise bout on -7 and -4 and then competition

76
Q

describe the modified supercompensation protocol ?

A

days -6 to competition slowly increasing carb intake, and slowly decreasing training

77
Q

what were the gender differences in supercompensation protocol ?

A

if you abide by the protocol there aren’t supposed to be any gender differences

78
Q

why is it important to eat familiar foods ?

A

because you can tolerate them well

79
Q

24h prior to exercise, what should you eat ?

A

high CHO meal (60-70% total kcal), familiar food `

80
Q

3-5h prior to competition, what should you eat ?

A

1-4.5g CHO/kg body weight

easily digestible food with low to moderate in fiber, and low GI

81
Q

what are CHO-rich protein sources that can be eaten 3-5 h before an event ?

A

yogurt, soy products, small amount of legumes

82
Q

is it ok to eat food 1h before an event ?

A

yes!

83
Q

what are 3 factors determining the glycemic response in exercise ?

A
  • insulin+ contractile activity increases glucose uptake
  • balance of inhibitory and stimulatory effects of insulin and catecholamines on liver glucose output
  • magnitude of intestinal absorption ongoing of ingested CHO
84
Q

intake of CHO 1h before exercise could lead to what ?

A

increase in CHO oxidation and glycogenlosys, suppression of fat metabolism as energy source.

85
Q

when is reactive hypoglycemia more prevalent ?

A

when you eat 75 min prior to exercise

86
Q

with ingestion 45 min or even 15 min prior to exercise, how does the risk of reactive hypoglycemia change ?

A

decreases

87
Q

how can reactive hypoglycemia be prevented ?

A

ingestion 5 min prior and warm up

88
Q

if a high GI food is ingested before exercise, what kind of effect does a CHO ingested during exercise have ?

A

it means that there will be little to no effect on metabolism- potential harmful effect of high GI food is reduced.

89
Q

what is the convincing evidence that carb feeding during exercise improves endurance capacity?

A

if you eat in exercise >45 min, it helps maintain blood glucose and CHO oxidation, spares glycogen in the liver and possibly in muscle, promotes glycogen synthesis, and affects the CNS

90
Q

does the frequency of CHO ingestion during exercise >45 min matter?

A

no, it doesn’t matter if it’s a bolus or several small amounts

91
Q

what is the optimal amount of exercise CHO feeding ?

A

needs to be the amount that brings maximal exogenous oxidation rates without any GI disturbance
up to 70g/h

92
Q

how many gCHO/l do sport drinks have

A

60-80 g/L

93
Q

solutions up to what % of CHO in sport drinks are tolerated during exercise w/o any GI disturbance ?

A

8% CHO

94
Q

70g CHO is in what quantity of sport drink ?

A

1 L

95
Q

70g CHO is in what quantity of bananas ?

A

3 bananas

96
Q

70g CHO is in what quantity of wine gum ?

A

120-150g

97
Q

70g CHO is in what quantity of powerbars with high protein and high CHO

A

1.5 bars

98
Q

how do you spare endogenous sources of CHO ?

A

by ingesting exogenous CHO

99
Q

true or false: rate of oxidation depends on whether it is a mono or disaccharides

A

false

100
Q

which monosaccharide is oxidized at a high rate

A

glucose

101
Q

what is a high rate of CHO oxidation ?

A

1g/min

102
Q

high rate of oxidation: 1M, 2D, 2P

A 
glucose
maltose
sucrose
maltodextrin
amylopectin (branch type)
103
Q

which will be broken down faster: branched CHO or single line ?

A

branched

104
Q

what will be broken down faster? amylopectin or amylose ?

A

amylopectin bc it is branched

105
Q

low rate of oxidation: 2M, 2D, 1P

A 
fructose
galactose
isomaltose
trehalose
amylose
106
Q

why are monosaccharides not all rapidly oxidated ?

A

galactose and fructose have to first convert to glucose

107
Q

where would you find trehalose ?

A

fungi, plants, invertebrate animals

108
Q

where would you find isomaltose

A

honey and sugarcane

109
Q

where would you find maltodextrin ?

A

starch breakdown

110
Q

how is exogenous carb oxidation related to exercise intensity

A

exogenous carb oxidation rate will increase with increasing exercise intensity to up to 50% VO2max
after that, may decrease

111
Q

why is it a good idea to combine 2-3 different CHO?

A

because if there is a lot of glucose, the transporters are saturated but fructose has a different transport mechanism. this enhances the rate of oxidation up to more than 1g/min

112
Q

what is a light solution if you’re likely to get hungry while exercising ?

A

gels slowing gastric emptying with 2+ CHO in them

113
Q

what could limit exogenous CHO oxidation in general ? (6) what is the main one ?

A
  • gastric emptying rate
  • digestion rate
  • ABSORPTION RATE in small intestine (main)
  • retention in liver
  • muscle glucose uptake
  • metabolism in muscle
114
Q

in exercise, why would there be a reduced digestion and absorption of CHO ?

A

because of reduced blood flow to gut

115
Q

how does exercise stimulate glucose uptake ?

A

for 1-2 hrs post exercise, due to increased insulin sensitivity

116
Q

high insulin stimulates glycogen synthesis by which enzyme ?

A

glycogen synthase

117
Q

what are the two post-exercise phases of glycogen synthesis ?

A

the initial insulin independent rapid phase

and then the insulin dependent slow phase

118
Q

what is the rate limiting enzyme of the rapid phase of glycogen synthesis ? what are its forms ?

A

glycogen synthase, existing in inactive D-form and active I-form

119
Q

when is glycogen synthase in what form ?

A

when glycogen concentrations are low - active I form

when glycogen is high- inactive D form

120
Q

what does exercise do to glycogen synthase

A

excites it

121
Q

after exercise, what proportion of glycogen is in the active I form ?

A

80%

122
Q

what is the rate-limiting substrate of glycogen in the rapid phase ?

A

UDP-glucose (activated glucose) availaibility

123
Q

what mineral enhances the rapid phase of glycogen synthesis

A

Ca2+ increases GLUT4 translocation

124
Q

when does the slow phase of glycogen synthesis begin ?

A

when the effect of the exercise-induced increase in glucose transport wears off, approximately 2h after exercise

125
Q

what does the glycogen synthesis rate in slow phase mainly depend on ?

A

insulin concentrations

126
Q

why is insulin with a more significant role in the slow phase of glycogen synthesis ?

A

because at this pt it is no longer suppressed by catecholamines

127
Q

muscle contraction enhances which phase of glycogen synthesis

A

both ! the effect lasts several hours

128
Q

glycogen: branched chained or line ?

A

branched

129
Q

what enzyme makes glucose into a branched chain ?

A

branching enzyme

130
Q

what does glycogen synthase do ?

A

combines excess glucose residues one by one into a polymeric chain for storage as glycogen.

131
Q

what does the branching enzyme do ?

A

adds branches to the growing glycogen molecule during the synthesis of glycogen

132
Q

what 3 main things does glycogen synthesis depend on ?

A

glucose availability,
transport of glucose into cell (exercise stimulation, insulin, muscle glycogen)
enzyme activity

133
Q

what is the effect of muscle glycogen on glycogen synthesis

A

when muscle glycogen concentrations are low, the enhanced glucose uptake has to last longer

134
Q

why is it better to eat CHO immediately post exercise vs 2hrs post exercise ?

A

because there will be a much more significant rate of glycogen synthesis in the first two hours

135
Q

what is the correlation between muscle glycogen resynthesis and carb intake ?

A

positive

136
Q

why does fructose take more time to result in glycogen synthesis ?

A

bc it has to be converted to glucose in the liver first

137
Q

what is the relative rate of glycogen synthesis post exercise from fructose, glucose, or sucrose ?

A

fructose takes more time

138
Q

will a high GI meal or a low GI meal post exercise result in more glycogen synthesis ?

A

high GI (higher absorption rate and availaibility of glucose)

139
Q

why can it be beneficial post exercise to include protein in the meal ? what is more important, though ?

A

some aa have an effect on insulin secretion

glycogen storage increases more when carbs ingested w protein, but adequate CHO is more important

140
Q

could caffeine positively affect carb ingestion after exercise ?

A

maybe

141
Q

what form of CHO post exercise is preferable

A

solid= liquid

142
Q

before exercise, what will mostly happen to carbs eaten ?

A

some will go to muscle glycogen but most to liver

143
Q

what is the best GI schedule for an athlete

A 
low GI (balanced meal w protein) in morning
high GI in competition and in evening
144
Q

what is the rate of CHO ingestion post exercise per min ? per hour ?

A
  1. 4g/min

1. 2g/kg bw /h for 3-4 h

Sport nutrition (EXCI 445) (17 decks)

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