Transcript Fat Intake and Athletic Performance

Fat Intake and Athletic
Performance
Remember...
• All energy systems are on at all times...
– At higher exercise intensities there is a shift
toward carbohydrate use.
– At lower intensities <65% VO2max, FAT is
oxidized to produce ATP.
But “low intensity” doesn’t mean that
carbohydrate use isn’t occurring...
Plasma Glucose
Energy Expended
Plasma FFA
IMTG
Muscle Glycogen
25%
65%
Exercise Intensity
85%
Ultra-Distance Performance Times
• Endurance exercise performance is limited
by an individual’s ability to sustain the
desired intensity late in exercise.
Example: Marathon Time
Anaerobic
Start of aerobic
CHO oxidation
10s, 30s...1 min
5 min
Beta (fat) oxidation,
level of CHO
oxidation depends
on intensity and
training status and
CHO availability
20min
90min
Almost all
available
glycogen is
gone, aa
breakdown
and liver
glycogen use
One
minute
left KICK
last 15min
Another approach to having “extra”
glycogen – train your body to use less
The alternative to maximizing the availability of CHO is to conserve
CHO by maximizing the capacity to oxidize fat. The essential
theory underlying this strategy is the reciprocal relationship
between FAT and CHO in terms of providing energy for exercise.
Glycogen
Triglyceride
Glucose
Pyruvate
Free Fatty Acid
Acetyl-CoA
Fatty Acyl CoA
TCA (Krebs) cycle
There are several potential sites where the entry of fatty acids
into oxidative pathways can be affected:
1.  entry of FFA into muscle by raising levels of FFA
in blood.
2.  entry of FFA into mitochondria by raising activity
of CPT-I (similar to GLUT4 but transports fat into
the mitochondria).
3.  intramuscular triglyceride stores and/or 
glycogen stores.
4.  capacity of the TCA cycle overall.
Studies of performance after high fat diets
Muoio et al (1994) gave 3 different diets (for seven days) in nonrandom
order to 6 trained runners.
Low CHO (LC): 40% CHO (6.6g/kg/d CHO)
High CHO (HC): 70% CHO (9.7g/kg/d CHO)
Normal (N): 60% CHO
VO2 max and submaximal endurance were highest on low CHO diet BUT
hard to interpret because there were only 6 subjects and diets given
in nonrandom order
Pogliaghi (1999) et al performed a similar study with 14 subjects (and
random order) and found no differences in performance after 4
weeks of diets with varied macronutrient composition.
Burke and Hawley (2001) report that 5-6 days
of a high fat diet (2.4 g CHO/kg/d vs 9.6
g CHO/kg/d) increases fat oxidation (and
glycogen sparing) during submaximal
exercise but results show no clear
benefits nor detriments to the
performance of prolonged endurance
exercise (though rate of perceived
exertion was higher).
High Fat vs. High CHO
p.144
Endurance Performance Time
CHO
FAT
Baseline
2 weeks
7 weeks
High Fat Diet but very low CHO
intake...Ketogenic Diets
Many variations but key elements are:
extremely low in CHO (<10% energy)
extremely high in fat (>60% energy)
protein varies a lot (10-40% kcal)
Theoretical advantages for athletes:
• High fat content may  intramuscular triglyceride storage
• Cellular adaptations to access and oxidize intramuscular
triglyceride may spare glycogen
• Production and utilization of ketones may further
spare CHO use
Improved submaximal performance??
Short Term Low CHO/High FAT and
Performance
Langfort et al (1996)
• 8 untrained men mixed or ketogenic (50% fat, 45 %
protein, 5% CHO) diets for 3 days and measured
performance and metabolic markers.
• Ketogenic diet did not lower VO2 max or lactate
threshold.
Ball et al (1996)
• 6 healthy males cycle until exhaustion (at ~95% of
max) after consuming a normal or ketogenic diet
(33.6% pro, 64.4% fat and 2.2% CHO) for 3 days
• Exercise time following the low CHO diet was shorter
than exercise time after 3 days of normal diet.
Hoppeler et al (2003)
• Highly trained du-athletes
• 5 weeks of high fat (~53%) or low fat (~13%) diets using
a randomized cross over design.
Long Term
They reported no change in:
• maximal aerobic or power capacity
• muscle glycogen levels
But changes in:
• increased intramuscular triglyceride (after high fat diet)
• lower blood lactate and RER (after high fat)
Overall: 2X increase in intramuscular triglyceride without
compromising glycogen stores
• Metabolic data indicate shift toward a larger utilization of
fat for energy: No effect on performance
• Lot of Variability between subjects
Summary of FAT Manipulations and
Endurance Performance Studies
1. How low in CHO depends on total energy.
2. Above a threshold (5g/kg/d??), no benefit of 
CHO on performance.
3. Humans may have greater capacity to oxidize fat
than often appreciated.
4. Adaptations occur fairly quickly (< 7 days)
How can athletes maintain
performance on CHO-restricted HIGH FAT DIET?
1. Increase IMTG = more fat use, conserve glycogen
2. On high-FAT diets (less than 2g CHO/kg/day or >50%
energy from fat), lack of CHO causes ketogenesis
Low insulin levels= very high rates of lipolysis (breakdown of
TG to FFA in adipose tissue). In liver, FFA are oxidized, reesterified, or converted to KETONES
Ketones can replace glucose usually required by brain (and
other tissues).Ketones could help maintain performance by
providing an alternate energy source for brain (and muscle)
that spares glycogen).
Do diets work long-term? Beside the point - athletes do not
use them this way
Is the diet actually low in CHO?
Some yes, some no, depends on the % of the diet that is
CHO but ALSO the total number of calories
2.
Is muscle glycogen lower?
Some yes, some no – depends on how low the diet really
was in CHO and the duration/intensity of the training.
3.
Is performance compromised?
Varies – partly due to lack of controlled studies – some
show improved performance with high fat, others show no
change, and other show worsening.
There may be no “true” response to high fat diets that will
hold true for 99% of the population.
Many studies had very “person-specific” results. The fact that
there were very different results from different subjects is an
important take home points Athletes, coaches, etc should
realize that each athlete may have a different response and
that just because the literature “says so” doesn’t mean that
one diet is the optimal diet for performance for everyone.
Fat Basics
• The average American consumes a diet that is
about 30% fat.
– High fat diet has been associated with an increased
risk of cardiometabolic disease.
– High fat diets are likely high calorie diets and increase
ones chance for weight gain over time.
• Athletes, decrease their risk of cardiometabolic
disease with regular exercise… they likely aren’t
negatively effected by overeating fat.
• In fact, athletic performance could be affected by
under-eating fat...
Fat is good...
• Fats are important for many metabolic processes:
– Energy production
– Transporters of lipid soluble vitamins
– Important in the synthesis of Vitamin D, cholesterol,
and steroid hormones.
– Structurally important in cell membranes
– Fat can be classified by its structure:
– Unsaturated: contain double bonds between carbons
• Includes the essential fatty acids that must be
consumed in our diet.
– Saturated: single bonds between carbons
• Linked with cardiovascular disease, should be
limited to less than 10% of total calories.
To little fat...<10%
• Risk of becoming deficient in essential
fatty acids and fat soluble vitamins.
• Could affect fat mobilization and oxidation,
important in energy production
• Lower circulating levels of hormones
(insulin, testosterone...important ones if
you want to build lean body mass)
Summary and Recommendations
Athletes eating a diet of 55-65% CHO should
consume 20-25% (30%?) fat.
Limit intake of saturated fat
“Good” fat sources:
Olive oil/Canola Oil, Seeds, Nuts, Fish, Avocado
For athletes who require high ENERGY intake,
increasing fat in the diet can be helpful to maintain
energy balance