Chapter 7- Fats Flashcards
1
Q
where is most fat found ? where is a small amount found ?
A
adipose tissue
small amount found in intramuscular triacylglycerol
2
Q
how many km can you run on fat stores
A
13 000 km
3
Q
why do you want to use fat instead of carbs
A
because you want to spare glycogen since fatigue is most closely related to glycogen depletion
4
Q
total fat approximately how many times more than carb stores ?
A
50 times
5
Q
what are the three sources of fat for energy ?
A
adipose tissue and muscle triacylglycerol
with a little bit of plasma TG from VLDL
6
Q
what are fats stored as ?
A
TG
7
Q
what enzyme breaks down fats ?
A
hormone sensitive lipase
8
Q
what happens to the fats once they are broken down ?
A
some are released into the circulation for reuptake, while some are reesterified.
9
Q
what happens to the glycerol from lipolysis ?
A
circulates in blood, taken up by liver and used for gluconeogenesis
10
Q
fats are the primary source of energy in these three states
A
rest
low to moderate intensity
during recovery between intense activity
11
Q
what does endurance training do to your fat use ?
A
improves it
12
Q
is fat an efficient fuel for muscles ?
A
no, especially at high intensities
13
Q
what will determine the principal source of exercise fuel
A
intensity of exercise
14
Q
the body has large stores of fat, but seems impossible to use fat as fuel. true or false ?
A
true
15
Q
what are the 6 rate-limiting steps of fat oxidation
A
lipolysis rate removal of FA from fat cells transport of fat in blood transport of FA into muscle cell transport of FA into mitochondria oxidation of FA
16
Q
in what form is HSL found in adipocytes ?
A
inactive form converted to active form depending on hormone mediation
17
Q
what hormones stimulate HSL
A
epinephrine (not NE)
18
Q
why does epinephrine stimulate HSL
A
because it is produced in adrenal medulla, especially during exercise
19
Q
what is the most important counter regulatory hormone to HSL activation ?
A
insulin
20
Q
why can’t the adipocyte reuse the glycerol from lipolysis and therefore most glycerol is released into the plasma ?
A
because the enzyme glycerokinase which phosphorylates glycerol for reesterification is very low concentrations
21
Q
what is the percentage of FA that are reesterified at rest ?
A
70%
22
Q
during exercise, is reesterification suppressed ?
A
yes, meaning there is more FA available
23
Q
why does FA availability increase in exercise ?
A
because reesterification is suppressed, and also b-receptors stimulate it (catecholamines)
24
Q
are FA soluble in aqueous environment ?
A
no
25
how are FA transported in plasma ?
bound to albumin
26
does lipolysis still happen in exercise ?
yes, but reesterification is suppressed
27
how can rate of lipolysis be measured?
concentration of glycerol
28
what are the three things which regulate FA reesterification ?
rate of FA removal from adipocyte (need to bind to albumin)
rate of glycerol-3-phosphate production (a byproduct of glycolysis, and related to alpha-glycerol-phosphate which decreases reesterification)
29
what is glycerol-3-phosphate ?
a byproduct of glycolysis, and related to alpha-glycerol-phosphate which decreases reesterification
30
what are 3 factors affecting the binding of FA to albumin ?
```
blood flow (the higher, the more transportation of fatty acids)
albumin concentration (responsible for transporting FA)
free binding sites (only 3 binding sites)
```
31
what enzyme is needed to release FA
lipoprotein lipase
32
what kind of lipoproteins do TG bind to ?
VLDL and chylomicrons
33
what percentage of energy expenditure during prolonged exercise is taken from VLDL ? what does this mean ?
3%
this means that VLDL and chylomicrons are a source of FA, we need lipoproteins to release them but it's a rather slow process and not a major contributor of energy
34
what can increase the use of lipoproteins as a source of energy
training and high fat diet
35
what are the two proteins involved in the transport of FA across the membrane?
```
plasma membrane FA binding protein (FABPpm)
FA transporter (CD36)
```
36
transporters into the membrane become saturated at what concentration of FA?
1.5 mmol/FA
37
how does CD36 work ?
fat transporter into membrane across sarcolemma, works a bit like GLUT4, translocates to plasma membrane.
in exercise, muscle is contracting, increasing presence of CD36 at membrane, meaning an increase of FA transport into the cell
38
how does FABPpm work ?
located at cell membrane across sarcolemma, allows FA to enter the cell but then needs to be bound to FABPc
39
what does muscle contraction do to the concentration of CD36?
increases the plasma membrane CD36 and decreases the CD36 in sarcoplasm (translocation to membrane)
40
what does FABPc do ?
transport of FA from sarcolemma to mitochondria
41
what muscle fibers have a higher content of IMTG?
type I
42
how does the location of lipid droplets of IMTG change with exercise?
in trained muscle, lipid droplets closer to mitochondria and more grouped
43
what does IMTG stand for ?
intramuscular trialglycerols
44
does muscle contain HSL?
yes, lipolysis happens in similar manner
45
if lipid droplets in muscle are closer to mitochondria, what is suggested happens to most of them in terms of energy?
oxidized
46
in what 2 ways does IMTG vary in trained or untrained person
location and size
47
what are FA released from IMTG bound to until they go to mitochondria ?
FABPc
48
what are the two words for CAT/CPT
carnitine acyl transferase
| or carnitine palmitoyl transferase
49
what is the first step for the transport of FA into the mitochondria ?
the binding of activated FA to carnitine
50
how do short chain and medium chain FA get into the mitochondrial matrix ?
they diffuse freely
51
how do long chain FA get into the mitochondrial matrix ?
they use the carnitine shuttle
52
what are the 4 things that affects b-oxidation ?
enzymes in pathway
concentration of TCA intermediates
TCA enzyme activity (many intermediates with NADH and ATP and other things promoting or inhibiting pathway)
presence of oxygen (MAJOR)
53
at rest, what is the overnight energy mostly consisted of ?
fat + most liver glycogen
54
what is the resting plasma FA
0.2-0.4 mmol/L
55
at rest, what happens to most fats after lipolysis?
most are re-esterified
| only half of FA entering blood stream are oxidized
56
during exercise, how does the rate of lipolysis change ? how ?
it increases threefold due to catecholamine stimulation
57
how does exercise catecholamine stimulation influence reesterification ?
decreases it
58
how does exercise catecholamine stimulation influence blood flow to adipose tissue
increases, meaning more of circulating FA
59
first 15 min of exercise, describe the plasma FA concentrations
they usually decrease because the rate of FA uptake by muscle is higher than rate of FA appearance from lipolysis
60
after 15 min of exercise, describe the plasma FA concentrations
FA appearance from lipolysis > oxidation, so there is a greater concentration of FA in blood because we are not utilizing all of it
61
what does increase in plasma FA depend on?
exercise intensity
62
during moderate intensity exercise, how high can the concentration of plasma FA become ?
1 mmol/L
63
during high intensity exercise, what kind of concentration of plasma FA do we see ?
not that high or absent increase in plasma FA since rate of fat oxidation decreases
64
at 25% VO2max, most energy comes from _______
plasma FA
65
at 65% VO2max, where does the energy come from ?
plasma FA contribution declines, increased TG contribution to almost half of fat being oxidized
66
at 86% VO2max, where does the energy come from ?
sympathetic vasoconstriction will decrease fat oxidation but rate of lipolysis still high
67
why does fat oxidation decrease at higher exercise intensities
sympathetic vasoconstriction will decrease blood flow
| lactate accumulation will increase rate of reesterification
68
explain the experiment with injection of lipid heparin
control group and group with injection of lipid heparin
lipid heparin will restore FA level with lipoprotein lipase as if you were in moderate physical activity. therefore, the lipid heparin group will have a higher FA concentration.
however, when it comes to fat oxidation, there is a very small difference. therefore, this shows there are other mechanisms controlling FA availability during exercise, other than simply FA concentration..
69
what are mechanisms that may control FA availability during exercise ?
limitations to transporting (eg long chain is carnitine dependent, can take time in high intensity exercise whereas medium chain oxidation is unaffected)
70
how does training affect lipolysis rate ?
it does not
71
how does training affect fat oxidation?
increase in mitochondrial density, oxidative enzymes, capillary density, CAT increase, binding proteins
72
how will IMTG change with training ?
percentage of energy used from glycogen will decrease after training while proportion of energy derived from fat will be larger
73
how will a high fat diet change fat oxidation
increase it
74
in the study with Burke et al 1999, what kind of diet was consumed ? what happened to RER ?
5 days high fat diet, then 1 day high CHO
baseline RER=0.9
day 5 RER= 0.82
1 day CHO RER=0.87 (still not restored to baseline RER)
therefore body adapts its metabolism to lower RER likely due to metabolic adaptations in muscle
75
what are the 5 factors affecting energy from different sources
```
exercise intensity
diet
duration
activity level
timing of food intake
```
76
what is the fastest way to alter fat metabolism during exercise ? what are the consequences ?
carb feeding
will increase insulin and therefore reduce lipolysis and cause reduction in FA availability and carnitine dependent transport
77
what did the Horowitz et al study do? what kind of diet was consumed? what happened ?
eat carbs 1 hr before exercise
lipolysis and fat oxidation were reduced, with plasma FA reduced too
measured via biopsy
however, when intralipid and heparin was introduced, followed by exercise, no difference in muscle glycogen before exercise but then after exercise at 70% VO2max it was seen that muscle glycogen spared in those who received intralipid
78
what kind of effect does carb feeding before exercise have on fat oxidation ?
reduces fat oxidation by reducing lipolysis and plasma FA(w insulin) and inhibits carnitine transport
79
if you label MCFA and LCFA, what will you see in the uptake of them if you are fasting?
high uptake of LCFA and MCFA
80
if you label MCFA and LCFA and also eat glucose, what kind of uptake of them will happen ?
MCFA uptake doesn't change
| LCFA uptake decreases bc depends on CAT transport
81
glucose intake inhibits uptake of which FA
LCFA
82
what is the classical explanation of the interaction between carb and fat metabolism? how does fat intake affect acetyl coA, pyruvate, PEP, PFK, hexokinase, G6P??
fat regulates carbs
therefore, increase in plasma FA will increase FA uptake and b-oxidation in mitochondria and breakdown to acetyl-coa
increased acetyl coA inhibits pyruvate dehydrogenase which breaks down pyruvate to acetyl coA (accumulation of phosphoenolpyruvate PEP)
increased acetyl coA will also increase citrate, which will inhibit PFK (reducing glycolysis, causing accumulation of G6P, inhibiting hexokinase and reducing muscle glucose uptake)
this also reduces Pi and AMP accumulation which usually stimulate glycogen phosphorylase
83
what is the caveat in the classical explanation of fat and carb interplay in metabolism?
the FFA in control group was <0.2 mmol/L
too low to provide tissues w sufficient fat substrate, so muscle glycogen breakdown may have increased in the control condition. the observed sparing of glycogen with the high FA in the experimental condition could have been biased
84
what compound increases muscle glycogen breakdown during exercise
nicotinic acid
85
what does the modern theory about fat and carb metabolism say in short ?
that it is carbs that regulate fat metabolism
86
increasing the rate of glycolysis ______ fat oxidation in the modern theory of fats and carbs
decreases
87
explain the modern theory about fat and carb metabolism that looks at malonyl coa concentration
increase in glycogenolysis means that there is going to be more acetyl coa in the mitochondria. some of this acetyl coa is converted into malonyl coa which inhibits CAT/CPT transporters and therefore the transport of FA into mitochondria is reduced, as well as the concentration of carnitine.
88
in the modern theory about fat and carb metabolism what are the two things that may inhibit fat oxidation ?
increase in acetyl coa converting to malonyl coa, as well as a reduction in intramuscular pH both inhibit the CAT
89
what is a more modern theory about fat and carb metabolism that depends on carnitine concentration?
the acetyl coa accumulated in an acceleration of glycogenolysis is bound to carnitine, meaning the free carnitine levels drop and less carnitine is availabile to transport FA into mitochondria.
90
what is a more modern theory about fat and carb metabolism that depends on pyruvate ?
pyruvate-derived acetyl coa competes with FA-derived coa for entrance into TCA cycle
91
rate of carb utilization is ___related to energy needs of working muscle, whereas rate of fat utilization is ___ regulated by energy needs of working muscle
carb use tightly related to the needs, unlike fat use, as no mechanisms closely match metabolism of FA to energy expenditure
92
what does fat oxidation depend on more- fat availability or energy needs of muscle ?
fat availability and rate of carb utilization
93
how does the digestion of fats compare to digestion of carbs in speed ?
digestion of fats slower (also slows down gastric emptying)
94
what fat does fish oil contain ?
LCFA omega-3
95
why should the intake of fat during exercise be avoided ?
because the primary roles of LCTG is in replenishing the IMTG stores after exercise, and the rate of breakdown of them during exercise is pretty low (won't be an efficient source)
96
how are MCTG usually consumed as a supplement ?
they have few natural sources, aren't stored in the body so athletes use them for energy to replace normal fat
97
what hormones and mechanism does fasting affect ?
increases plasma catecholamines, which stimulates lipolysis, more plasma FA and less glucose turnover
98
what effect does fasting have on exercise performance at <45% VO2max ?
no effect
99
what effect does fasting have on exercise performance at 50-100% VO2max ?
decreases endurance, in a non-reversible way (even with CHO ingestion during exercise)
100
in the study which looked at performance in fasting athletes, what was the caveat ?
control group had last meal 3 hours before exercise, and therefore it was an unfair comparison bc it would have affected the endurance capacity
101
in a fast of 12 hrs compared to a fast of 24 hrs, what kind of difference was seen in exercise performance
same decrease in performance + acidosis
102
what are the two reasons fasting may decrease endurance ?
depletion of liver glycogen and metabolic acidosis
103
what is metabolic acidosis
ketones lower pH
104
what did a short term high fat diet show in exercise performance if a high fat diet was eaten hours before ?
the research was inconclusive. no effect on endurance capacity or decreased endurance
105
what did a short term high fat diet eaten days before exercise do?
less than 2 weeks on high fat diet found that it is too short of an adaptation, will impair exercise capacity and is therefore ineffective
106
how long does a diet have to be to be considered long term
2 weeks or more
107
what is the rationale behind a high fat diet ?
adaptations for better capacity of fat oxidation: increasing oxidative enzymes, less use of liver glycogen
108
explain the Phinney et al long term high fat diet conditions of study
n=5
| diet was 85% fat vs 65% carbs for 28 days, and exercised submaximally (62-64% Vo2max)
109
explain the Phinney long term high fat diet study conclusions when it comes to exercise time, resting muscle glycogen, and fat oxidation
no difference in exercise time
the HFD brought 50% less resting muscle glycogen
RER was lower in HFD (0.72) which would mean greater fat oxidation at 60% VO2Max
110
explain the 3 caveats in Phinney's long term HFD study
in general, trained subjects can ride for a very long time
small sample size w large variability (one person rode for 60% longer after HFD)
intensity was low, not a competitive intensity and reduced carb stores are not limiting
111
explain the Helge study with HFD and HCD
after 7 weeks of endurance training w a HFD, some switched to a high carb diet. although in the ppl who switched their endurance was better, they still did worse than those who were on a high carb diet for the 7 weeks
therefore, the high carb switch did not reverse the effects, suggesting that the negative effects of HFD caused not only by lack of carb as fuel but also suboptimal adaptations to training
112
a study found reduced pyruvate dehydrogenase after fat adaptation. why?
increase in fat oxidation partly caused by reduction in ability to oxidize carbs
113
what kind of fat recommendations for pre-workout meal
fat is good bc reduces hunger before exercising, but too much can increase GI issues
therefore for snacks <4hrs before exercise choose low unsaturated fats
114
what is the AMDR for fats
20-35% total
115
what is the AMDR for fats for athletes
20-30% of total
116
what are the recommendations of saturated fat for general populations ?
<10% AMDR to reduce CHD risk
117
what are the recommendations of monounsaturated fat for general population ?
10-15% AHA 10% NCEP AMDR
118
what are the recommendations of polyunsaturated fat for general population?
10% AMDR
119
what kind of fat should be eaten post exercise
fat consumption not essential, but minimal fat intake recommended to ensure optimal digestion
120
how many carbons are LC TG
16-18
121
what is the dose limitation for LC TG and MC TG ?
30g max tolerable, more than 50g leads to GI distress
122
in a study by Ivy et al, LCT or MCT were ingested before moderate exercise. what happened ?
LCT increased serum TG but no effect on rate of FA oxidation.
123
in a study by Satabin et al, LCT or MCT was ingested before exercise w isotope tracers. what happened ?
MCT associated w rise in ketone bodies, and small amount of LCT was oxidized
124
why is LCT ingestion during exercise not desirable ?
slow gastric emptying and enter circulation in chylomicrons which is believed to be a negligible fuel source in ezercise
125
why does fasting still bring on fatigue if it increases fat availability
bc glycogen stores depleted, so even if fat oxidation increases, it's compromised
126
so, is MCT supplementation helpful ?
not really
127
what is the supposed benefit of fish oil? is it true
increase VO2max
| not true
128
what is the known benefit of fish oil ?
improves membrane characteristics and function
129
name 6 supplements claiming to increase fat oxidation
```
caffeine
pyruvate
carnitine
vanadium
chromium
dihydroxyacetone
```
130
what is the claim of caffeine to improve fat oxidation
increases epinephrine / decreases adenosine receptors, therefore more lipolysis and more FFA uptake and oxidation and spare glycogen
131
what are the findings on caffeine supplementing fat ozidation
glycogen sparing is a thing but occures with a dose of 6mg/kg at more than 70% vo2max
132
how many mg caffeine in coke ?
46 mg
133
how many caffeine in red bull ?
8 mg
134
how much caffeine in Starbucks ?
250 mg
135
under what form is caffeine more effective ? what is the catch?
caffeine pills but may cause heart palpitations
136
what is carnitine synthesized from (2)?
methionine and lysine
137
what are 3 sources of carnitine ?
meat, poultry, fish
138
what is the effect of carnitine supplementation on fat oxidation ?
no effect, useless
139
so, conclusion; chronic fat diets, yay or nay?
nay
| little evidence the hypothesis is true
