Download Fat: An Important Energy Source During Exercise

Fats
Chapter 6
Functions of Fat
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Fuel for cells
Organ padding and protection
transport fat-soluble vitamins
Constituents of cell membranes
Constituents of hormones
Categorization of Fats
• Degree of Saturation
– Saturated
– Monounsaturated
– Polyunsatrated
• Chain Length
– Short
– Medium
– Long
Saturated Fat
• Lacks C-C double
bonds
• Saturated with H
• Animal fat & tropical
oils
• Most unhealthy
• Hydrogenated oils
Monounsaturated Fat
• Contains single C-C
double bond
• Most healthy
• Most common
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Olive oil
Canola oil
Peanut(s) oil
Walnuts
Almonds
Polyunsaturated Fat
• Two or more C-C
double bond
• Omega 3
– Flax oil, Fish oil
– -linolenic acid
• Omega 6
– Corn, soyben,
safflower, sunflower
– Linoleic acid
Hydrogenated Fats
• Process used to convert unsaturated oils
into saturated oils
– Increases temp at which oil burns
– Increases shelf life
– Stays in mixture better
• Health impact is same as saturated fats
Trans Fatty Acids
• Formed from hydrogenation process
• May have worst health impact of all fats
TABLE 5.1 Fatty Acids in fats and oils
Oil/Fat Saturated Mono-unsat
Polyunsat
Beef
50
43
4
Chicken
30
46
22
Tuna
27
26
37
Olive
14
74
9
Canola
6
62
30
Tuna
27
26
37
Coconut
87
6
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Fatty Acids by Chain Lengths
• Short Chains
– 6 or less carbon atoms
– Found in butter, coconut oil, palm kernel oil
• Medium Chain
– 8 or 10 carbons
– Absorbed into blood more quickly
• Long Chain
– 12 or more carbons, most are 16 and 18
– Most common in the diet
Key Terms
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Lipolysis
Triglycerides (triacylglycerols)
Glycerol
Gluconeogenesis
– Lactate
– Glycerol
– Alanine
• 3500 kcal = 1 lb fat
Sources of Triglycerides/Fatty
Acids for Fuel
• Adipose tissue
– 140 lb @ 3% fat = 20,000 kcal
– 280 lbs @15% fat = 170,000 kcal
• Muscle Triglycerides
– 2,000 - 3,000 kcal
– Supplies energy at 1/3 rate of CHO
• Plasma triglycerides
– Minimal contribution (40 kcals)
Characteristics of Fat That Make It
Preferential to CHO as a Fuel
Substrate Reserve
• 2+ X as much energy per gram
• Not hydrated when stored
– 3 g H2O per g glycogen
– Equivalent energy as glycogen would
increase body weight by 50% or more
Glycerol-3-phosphate
HSL
EPI
Figure 1. Storage and mobilization of stored
triglycerides.
FFA Availability
• At rest, 70% of all FFA released during lipolysis
are re-esterified.
• During exercise, re-esterification is suppressed
by 50% which increases FFA avaiability.
• Exercise increases lipolysis (300%) which
contributes to the plasma FFA.
• Blood flow to adipose tissue and to muscle is
increased increasing overall delivery of FFA
FFA Transport into Muscle
• Protein carrier mediated process
• Carriers become saturated at high plasma
FFA levels (1.5 mmol/liter)
• Muscle contraction increases the activity
of the carriers which increases the
transport of FFA into the cell.
Intramuscular Triglycerides (IMTG)
• Type I muscle fibers have higher
concentrations.
• Endurance training translocates the IMTG
next to the mitochondria
• Lipolysis of IMTG mediated by HSL and
inhibited by insulin, just like in adipose
tissue.
Training
Fig. 2.
Contribution of
the four major
fuel substrates
to energy after
30 min of
exercise at
25%, 65%, and
85% of VO2max
in fasted
subjects.
Figure 3. Expanded
view of the sources of
fat for oxidation
during exercise at
25%, 65% and 85% of
VO2max in fasted
subjects.
Fig. 4. Substances providing energy during exercise at a
given absolute intensity of 65% VO2max before and after 12
weeks of training.
Fat Oxidation and Exercise
Duration
• Fat oxidation increases as duration
increases
• Maximal oxidation rates are approximately
1.5 g/min.
• Fat oxidation increases probably because
glycogen goes down.
Fat Oxidation and Intensity
• Fat oxidation rates peaks at ~ 60-65%
VO2max and then declines
• At low intensities (25% VO2max), most fat
is from adipose tissue
• At 65% VO2max, most is from IMTGs
• At high intensities, fat oxidation is
suppressed
Why is Fat Oxidation Suppressed
at Higher Exercise Intensities?
• Reduced blood flow to adipose tissue due
to sympathetic constriction of vessels
• Lactate increases re-esterification of FAs
• Transport into mitochondria is reduced
Muscle Adaptations Which
Enhance Fat Use
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Increase in enzymes of beta-oxidation
Increase of ETS capacity
Increase sensitivity of SNS stimulation
Increase in transport mechanism across
sarcolemma and within muscle
Systemic Adaptations Which
Enhance Fat Use
• Decrease in insulin
• Decrease in lactate
• Increase delivery of substrate
– Cardiovascular
– Capillarization
Recommended Consumption of
Dietary Fat
• Essential fatty acids must be supplied in the diet
– Linoleic acid (omega-6 fatty acid)
• 3-6 grams per day
• Supplied if 5-10% of calories are from fat
– Sources
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1 tablespoon of corn oil
2 tablespoons of sunflower oil
2.5 tablespoons of canola oil
5 tablespoons of olive oil
• Alpha-linolenic Acid (omega-3 fatty acid)
– 1-2% of kcal consumption
– 2-3 grams for 2000 kcal diet
– Sources
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1.5 teaspoons Flaxseed oil
1.5 tablespoon canola oil
3 tablespoons soybean oil
12 oz cod, flounder, haddock, halibut, tuna
6 oz salmon
3.5 oz herring, mackerel, sardines
Daily Recommendation for Fats
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Less than 30% of total calories for most
Less than 10% of calories as saturated fat
Adequate essential fats
Most fat should be monounsaturated with
polyunsaturated as second choice
Fat Supplementation During Exercise
• Cannot consume FFA because they are
too acidic and require protein carrier for
absorption
• LCT are slowly absorbed and rate of
uptake by muscle is slow
• MCT are directly absorbed and easily
transported into muscle
– 30 g is limit of tolerance
– Practically can contribute no more than 10%
of total energy
Short-Term Dietary Fat
Supplementation Before Exercise
• Consuming high fat diet increases fat
utilization but reduces exercise intensity
that can be tolerated
• Consuming high GI CHO just prior to
exercise will inhibit fat utilization during
first 50 min of exercise and increase use
of blood glucose
Long-Term High-Fat Diet and
Exercise Tolerance
• Exercise duration may be increased at
intensities <65% VO2max
• Durations at competitive intensities are not
improved
Combined Fat and CHO Loading
• No demonstrated beneficial effect of
combining high fat diet in days before
exercise and CHO loading immediately
before exercise.
Fat Intake During Recovery
• Requires 2gm/kg to resynthesize IMTG
• Take ~ 22 hrs to resysnthesize
• Optimizing IMTG may compromise CHO
Carnitine Supplementation
• Facilitates transport of LCT into
mitochondria
• Found primarily in animal products,
especially meat
• Consensus is that carnitine is not
ergogenic
Caffeine
• Likely will produce a glycogen sparing effect and
direct effect on CNS resulting in reduced fatigue
• Increases plasma FFA levels but not necessarily
fat metabolism
• Effect is greatest in naïve caffeine users
• Effective dosage begins @ 100-300 mg
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Coffee : 100 to 150 mg per cup
Cola: 35-55 mg per 12 oz
Tea: 20-50 mg per cup
Vivarin: 100-300 mg