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Fat race

Presentation sports nutrition research group March 20th
by

Heleen Evers

on 20 March 2014

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Transcript of Fat race

Current research, claims and practices promoting dietary fat for endurance performance
Source: Paleohacks.com
Source: Behance.net
The CrossFit prescription is a low-glycemic diet and consequently severely blunts the insulin response.
www.crossfit.com
PRO
CHO
FAT
30%
40%
30%
lean
low GI
high MUFA
Avocado
Olive oil
Coconut
http://simplesciencefitness.com
http://www.ketogenic-diet-resource.com
Van Proeyen K, Hesselink M, et al. High-fat diet overrules the effects of training on fiber-specific intramyocellular lipid utilization during exercise.
In: J Appl Physiol 111 (2011): 108–116.
Background
:
Increased pre-exercise dietary fat supply stimulates energy provision via fat oxidation during exercise. Chronic exposure to a high-fat diet (HFD) enhances the use of free fatty acids (FFA) in endurance exercise. Thus FFA oxidation can be stimulated with appropriate
chronic
exercise and/or nutrition (e.g., HFD), which upregulates pivotal steps in FFA catabolism.
However, it is still unclear whether these adaptations are specifically due to the
increased FFA
supply per se or result from
decreased glucose
availability.

Study goal
: to investigate the effects of endurance training in the
fasted state vs. training with carbohydrate intake
before and during training sessions on intramyocellular lipid (IMCL) and glycogen utilization during a
period of a hypercaloric HFD
.
Methods
: a comparison of the effects of endurance training in the fasted state (F) vs. the fed state (ample carbohydate intake) on exercise-induced IMCL and glycogen utilization during a 6-wk period of a hypercaloric fat-rich diet (+ 30% kcal/day; 50 EN% fat)
Fasting: a specific nutritional condition for stimulating FFA supply (relative to carbohydrate supply) to muscles during exercise.
2 classical nutritional interventions have been used to stimulate energy turnover via fat oxidation
A High-Fat Diet: increases energy provision via fat oxidation both at rest and during exercise.
Inadequate carbohydrate intake between training sessions often results in muscle glycogen depletion, which can also alter the metabolic responses to training, independent of increased dietary fat intake.

Therefore, metabolic adaptations elicited by a hypercaloric high-fat diet while maintaining adequate carbohydrate supply, may be different from the effects of isocaloric high-fat and (necessarily) lower-carbohydrate diets.
Previously...
The metabolic processes of substrate utilization during exercise
Muscle glycogen is the primary energy substrate in high-intensity endurance exercise. Success in endurance competitions often depends on the capacity for high-rate ATP production via glycogen breakdown.
E.g. in the decisive episodes of the competition, such as the pace accelerations when approaching the finish line.
# studies have clearly indicated that the consumption of a
high-fat diet
impairs the capacity for energy production via glycogen breakdown, even when muscle glycogen stores are ample.
Such adaptation is detrimental to endurance exercise performance.
This study demonstrated that net muscle glycogen breakdown during exercise in the
fasted state
is enhanced compared with exercise with exogenous carbohydrate supply before and during exercise.
The authors speculated that
fasting exercise may be an effective strategy
for stimulating energy provision via fat oxidation, while maintaining the intact potential for glycogenolytic ATP production.
De Bock K et al. "Type-specific muscle glycogen sparing due to carbohydrate intake before and during exercise." in: J Appl Physiol 102 (2007): 183–188.
Previously...
Diet-training trials
Several recent studies have challenged the idea that a high-carbohydrate eating strategy is the best approach to maximize the outcomes of chronic adaptations to training. These investigations have reduced carbohydrate availability during structured training interventions using two different approaches:
lowering muscle glycogen concentrations by rescheduling training sessions
lowering exogenous carbohydrate supply by undertaking training sessions in a fasted state

These strategies provide evidence of greater training-induced metabolic adaptations with low-carbohydrate availability but deliver inconsistent results with respect to improvements in exercise capacity (intensity) or endurance performance (time to exhaustion).

It has been difficult to apply findings to the preparation of well-trained athletes, partly due to the lack of direct relevance of study protocols to the characteristics and practices of endurance athletes, e.g. using untrained subjects, low-volume training programs and repetitive exercise stimuli instead of working to perceptions of effort or incorporating progressive overload.

A final and important difference is the complexity by which well-trained athletes manipulate carbohydrate availability via combinations of dietary practices, both in training settings and competition (as documented in dietary surveys of endurance athletes, typically reporting the intake of carbohydrate during and after daily workouts.
A critique on diet-training studies: issues with real-life applicability
Chronic diet-training studies investigating different daily carbohydrate intakes: an apparent disparity in research finding
Enhanced performance of prolonged exercise after a period of training on a high daily carbohydrate intake
No differences found between exercise performance on a high or moderate daily carbohydrate intake
E.g. Achten J, Jeukendrup AE, et al. Higher dietary CHO content during intensified running training results in better maintenance of performance and mood state. J Appl Physiol 96 (2004): 1331–1340.
E.g. Vogt M, et al. Effects of dietary fat on muscle substrates, metabolism, and performance in athletes. Med Sci Sports Exerc 35 (2003): 952–960.
1) providing additional CHO in the HC treatment during daily training to maximize carbohydrate availability during exercise
2) normalizing muscle glycogen stores before exercise testing to differentiate between the acute and chronic effects of
consuming a moderate- versus high-carbohydrate diet

Does this have any practical significance?
Yes: endurance athletes typically undertake strategies to normalize muscle glycogen stores before competition.
Protocol: 8 trained subjects performing
Fat-adapt (5d/1d)
HCHO (6d) - isoenergetic diet
Day 7: 1h cycling @ 70% VO2max.

Muscle biopsies immediately b&a exercise
A short-term (1 wk) manipulation of
dietary macronutrient intake

is associated with significant changes in:
skeletal muscle gene expression;
substrate stores;
metabolic flux;
fuel oxidation.

Exercise training
also results in striking modifications in:
muscle gene expression;
energy reserves;
the relative contribution of fuels to the energetic demands of muscle.
The effects of a practical "dietary periodization" strategy in well-trained endurance athletes on selected aspects of metabolism and exercise performance.
A 5-day high-fat diet followed by 1 day high-carbohydrate intake increases rates of fat oxidation and decreases rates of muscle glycogenolysis during submaximal cycling compared with consumption of an isoenergetic high-carbohydrate diet for 6 days.
Background
:
Diet-exercise manipulation that results in low muscle glycogen content is associated with increased resting AMPK activity (compared with high-glycogen stores). Could these diet-exercise strategies also result in significant changes in muscle lipid availability?

Results
:
Fat-adaptation followed by carbohydrate-restoration will increase resting muscle TG concentration, and changes in lipid availability will modify AMPK signaling at rest and during exercise.

Conclusion
:
The changes in AMPK activation observed in the present study could be due to altered fuel status (increased muscle lipid availability), a greater adaptive response when training with low muscle glycogen availability or, most likely, the interactive effects of both of these factors.
Endurance athletes consume large amounts of CHO in the
belief
that training longer and/or more intensely, as a result of increased glycogen availability, will promote superior training adaptations.
Achten J, Jeukendrup AE et al. Higher dietary carbohydrate content during intensified running training results in better maintenance of performance and mood state. J Appl Physiol. 2004;96(4):1331-40.
Hawley JA, et al. Promoting training adaptations through nutritional interventions. J Sports Sci. 2006;24(7):709-21.
Regular endurance training
induces a number of adaptations that enhance performance
Altered gene expression
via an accumulation of specific proteins
Adaptations
increased mitochondrial volume
increased capillary density
greater activity of oxidative enzymes (CS, beta-HAD)
Response
Increased VO2max
substrate metabolism shift from CHO (glycogen) to lipid oxidation

Processes underlying the adaptive response to endurance exercise
Hansen AK, et al. Skeletal muscle adaptation: training twice every second day vs. training once daily. J Appl Physiol. 2005;98(1): 93-9.
Murakami I, et al. Significant Effect of a Pre-Exercise High-Fat Meal after a 3-Day High-Carbohydrate Diet on Endurance Performance. Nutrients 2012, 4, 625-637
Enhanced
performance
Commending an acute bout of endurance exercise with LG induces a greater increase in the transcriptional activity of several metabolic genes*

Untrained subjects who completed 10 wk aerobic training commencing with low muscle glycogen had*

more pronounced increases in resting muscle glycogen content and CS activity
a twofold greater increase in exercise capacity (time to fatigue)
Several research papers dating from 2001-2002
*when compared with (the same volume of) exercise performed with normal muscle glycogen stores.
Research from Hansen et al. (2005)
Under certain circumstances, training with LG can be beneficial
Caveats: # study details make it difficult to extrapolate these findings
untrained subjects --> will "training low" translate into improved adaptations in already well-trained athletes? [unknown]

Fixed amount of work in each training bout even though higher glycogen stores would allow more exercise and/or higher intensities

Results from a single leg kicking exercise are hardly comparable to a competitieve sport
"Further research is clearly needed before glycogen depleted training can be recommended as a practical strategy to enhance training adaptations and performance in already well-trained athletes."
The perfect diet for optimal performance
High CHO diet
Carbohydrate (muscle glycogen) is the predominant substrate utilized during prolonged exercise at intensities above VO2max.
Increased muscle glycogen content
ensuring an ample exogenous glucose supply as fuel for the working muscle
Delayed onset of fatigue
because glycogen depletion is prevented, provided the exogenous carbohydrate source is continuous
Performance can be maintained
even during prolonged periods of intensive training
RESEARCH?
Controlled diet-training trials
using specific training models
The potential role of altered substrate availability on gene regulation?
What makes a great athlete?
Talent
Training
Endurance training?
VO2max
mitochondial & vascular capacity
muscle density
...
Diet
Athletes achieve peak performance by training and eating a variety of foods.
Athletes gain most from the amount of carbohydrates stored in the body.
Fat also provides body fuel; use of fat as fuel depends on the duration of the exercise and the condition of the athlete.
Exercise may increase the athlete's need for protein.
Water is a critical nutrient for athletes. Dehydration can cause muscle cramping and fatigue.
Performance enhancement
Speed: time to completion of set amount of repetitions
Intensity: number of repetitions performed during a set time frame
Stamina: time to exhaustion
Adaptation
exercise-induced
diet-induced
Muscle glycogen: the essential fuel
Glycogen
High muscle glycogen
availability
or "training high"
Lipids
Low muscle glycogen
availability
or "training low"
Substrates for the working muscle
How does muscle substrate utilization relate to dietary macronutrient intake?
2010
2012
2011
2008
"Training low" trial on trained subjects
Hulston C, Jeukendrup AE, et al. Training with low muscle glycogen enhances fat metabolism in well-trained cyclists. Medicine & Science in sports & exercise 42/11 (2010): 2046-2055.
Which are the potential mechanisms underlying shifts in substrate utilization during exercise?
High-Fat meals after Carbo-loading
Colombani et al.
Carbohydrates
and exercise performance in non-fasted athletes: A
systematic review
of studies mimicking real-life. Nutrition Journal 2013, 12:16.
"Training low" trials on untrained subjects
Yeo WK, Burke LM, Hawley JA, et al. Skeletal muscle adaptation and performance responses to once a day versus twice every second day endurance training regimens. J Appl Physiol. 2008; 105(5):1519-26.
Dietary periodization: FA vs. HCHO
Yeo WK et al. Fat adaptation followed by carbohydrate restoration increases AMPK activity in skeletal muscle from trained humans. J Appl Physiol 105 (2008): 1519–1526.
Investigating the effects of different macro-nutrient intakes on exercise performance
and future research
Under certain circumstances, training with low muscle glycogen availability can be beneficial
Hansen AK, et al. Skeletal muscle adaptation: training twice every second day vs. training once daily. J Appl Physiol. 2005;98(1):93-9.
High CHO (n=9)
Low CHO (n=9)
3 week trial
Trial workouts
(1) 90' @ 70% VO2max (aerobic)
(2) 8x5'/1' 90-5% VO2max (HIIT)
! @ self-selected intensities
once daily, alternating workouts (day 1=(1); day 2=(2); repeat)
twice every 2 days, in succession (day 1=(1)+(2); day 2=rest; repeat)
Research Q?
muscle adaptation
substrate metabolism
exercise performance
increased
beta-HAD protein content and smaller change in GLUT4 levels, suggesting:
increased
capacity for fatty acid (muscle TG) oxidation, maybe due to:
enhanced
metabolic adaptations in skeletal muscle
less increased
capacity for CHO oxidation, resulting in changes in substrate metabolism during steady-state exercise
reduced
training intensity (HIIT) & in terms of performance
no more effective
than training with high muscle glycogen.
First study to look at the effect of training with low muscle glycogen on the glucose transporter GLUT4
(the rate-limiting enzyme in muscle glucose utilization).
"Training low" may be
counterproductive
for athletes who compete in
high intensity events
where CHO oxidation plays a significant role in performance, but may be
suited
in preparation for ultra-endurance activities.

"Training low" does NOT appear to be a worthwhile benefit for the well-trained athlete. Whether the
increased capacity for fat oxidation translates into better performance
during a longer duration test or following a longer period of adaptation remains to be seen.
Protocol
: single-leg knee extensor exercises (1h @ 75% VO2max) for 10 wk
Results
: greater time to fatigue in the glycogen-depleted leg
This study used a human model of "dietary periodization" in well-trained athletes to study the effects of diet-exercise interactions on muscle signaling & metabolism.
Burke LM, et al. Effect of
fat adaptation
and carbohydrate restoration on metabolism and performance during prolonged cycling. J Appl Physiol 89: 2413–2421, 2000.
Carey AL, et al. Effects of fat adaptation and carbohydrate restoration on prolonged endurance exercise. J Appl Physiol 91: 115–122, 2001.
Stepto NKCA, et al. Effect of short-term fat adaptation on high-intensity training. Med Sci Sports Exerc 34: 449 – 455, 2002.
Burke LM, et al. Adaptations to short-term high-fat diet persist during exercise despite high carbohydrate availability. Med Sci Sports Exerc 34: 83–91, 2002.
Cameron-Smith D, et al. A short-term, high-fat diet up-regulates lipid metabolism and gene expression in human skeletal muscle. Am J Clin Nutr 77: 313–318, 2003.
Stellingwerff T, et al. Decreased PDH activation and glycogenolysis during exercise following fat adaptation with carbohydrate restoration. Am J Physiol Endocrinol Metab 290: E380 –E388, 2006.
**Current sports nutrition guidelines recommend that endurance-trained athletes undertake their daily training sessions with high-carbohydrate availability.

Burke LM. The IOC consensus on sports nutrition 2003: new guidelines for nutrition for athletes. Int J Sport Nutr Exerc Metab 13 (2003): 549 –552.
Position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine (2009).

However, the results of several recent studies have challenged the idea that this is the best approach to
maximize the outcomes of chronic adaptation to training
.
Let Them Eat Carbs?
Yeo WK, Hawley JA, et al. Fat adaptation in well-trained athletes: effects on cell metabolism. Appl. Physiol. Nutr. Metab. 36: 12–22 (2011)
The fat-adapted group had - compared with HCHO -

increased resting muscle TG stores and AMPK activity;
resulted in higher rates of whole body fat oxidation;
reduced muscle glycogenolysis ("glycogen sparing");
attenuated the exercise-induced rise in AMPK activity.
n=21 M & F endurance-trained runners
Random cross-over trial with controlled isoenergetic diet + training regimen
LFAT (10% fat) for 3 days
MFAT (35% fat) for 3 days
7th day: glycogen normalization protocol
8th day: performance test
1) 90min preload run @ 62 VO2max
2) 10 km time trial run
Low-fat diet & endurance performance
Does the acute consumption of a very-low-fat diet impair endurance performance (relative to a moderate-fat diet) & are lipid profiles unfavorably altered?
Larson-Meyer E, et al. Effect of Dietary Fat on Serum and Intramyocellular Lipids & Running Performance. Med Sci Sports Exerc. 2008;40(5): 892-902.
Even a short-term consumption of a low-fat diet may unfavorably alter serum lipids compared to an isocaloric medium-fat diet, even in healthy, endurance-trained runners.
What is the effect of the macronutrient composition of pre-exercise meals on endurance performance?
Murakami I, et al. Significant Effect of a Pre-Exercise High-Fat Meal after a 3-day High-Carbohydrate Diet on Endurance Performance.
Nutrients 2012, 4, 625-637.
A review of recent short-term diet-training strategies
Trial protocol: cross-over design, wk intervals
Baseline diet: HC @ each meal (3 d)
1000 kcal meal @ 4 h before exercise
HFM (F 55; C 30 EN%) -- intervention
+ maltodextrin jelly (M)
+ placebo jelly (P)
HCM (F 20; C 70 EN%) -- control
+ placebo jelly (P)
Time trial (running) -- until exhaustion
How to explain the finding that the time trial performance was still improved by a similar extent in both groups after the training period?
the amount of work performed during training may not be critical
the additional "stress" of "training low" compensates for a slight reduction in physical performance during training
Future research...
Purpose:
Maintaining a high daily carbohydrate intake while altering carbohydrate availability for exercise.
Protocol: a rescheduling of training times for the intervention training model
Lowering muscle glycogen concentrations for half of the sessions by having subjects perform 2 successive training bouts (2nd bout commences with depleted muscle glycogen stores).
[HULSTON 2010]
Same performance times following the two diet treatments!
"Very low fat"? Purpose: lowering IMCL stores up to approx. 30%, with muscle glyogen stores raised to +22% at the start of performance testing.
LFAT
increased fasting TG
increased total:HDL cholesterol
MFAT
lowered fasting TG
lowered total:HDL cholesterol
CHO fed vs. fasted training on a HF diet
Dietary carbohydrate
Endurance athletes are advised to:
employ the carbo-loading method [SALTIN 1967 & SHERMAN 1981] and,
ingest a high-carb meal on the day of a race to
enhance carbohydrate storage
. [Position statement]
Improved endurance performance
because of the increased glycogen concentration before exercise. Prolonged exercise is associated with the depletion of the muscle glycogen in the working muscle. [BERGSTROM 1967]
Increased muscle & liver glycogen concentrations
following the ingestion of a high-CHO diet approximately 3 h before exercise [WEE 2005, NILSSON 1973] and thereby contributing to normal blood glucose concentrations during exercise.
Glycogen vs. Free Fatty Acids
Glycogen storage levels can
peak
after glycogen loading so that muscle glycogen may not further increase, even if large amounts of CHO are ingested on race day. [SALTIN 1967]
Raised blood insulin
If there is an intake of high levels of carbohydrates before exercise (after glycogen loading) then a rise in blood glucose might occur, resulting in an elevation of insulin that may persist.
Rapid depletion of glycogen during exercise
Inhibition of FFA mobilization
...thereby negatively affecting performance.
The extent to which
acutely altering substrate availability
might modify the training impulse has been a key research area for the past decades among exercise physiologists and sports nutritionists.

Evidence is accumulating that nutrient manipulation can serve as a potent modulator of many of the
acute responses to endurance exercise
.
[HANSEN 2005]
In summary
Dietary Fat
The intake of a high-fat meal before exercise increases blood FFA levels when compared with those levels derived from ingestion of a high-carb meal [OKANO 1996]
Muscle glycogen levels are conserved
during endurance exercise

[COSTILL 1977, DYCK 1993 & 1996, VUKOVICH 1993]
Increased blood FFA concentration
contributes to an increase in lipid metabolism
Hypotheses
:
After maximum muscle glycogen storage by carbo-loading, the intake of a HFM on race day may help to improve performance (compared to a HCM).
Carbohydrate intake just before starting to exercise has a conservation effect on muscle glycogen, thereby further enhancing performance.

Purpose
:
To investigate the effects of a HFM and a HCM 4 h prior to exercise after ingesting a high-carbohydrate diet for 3 days, based on previous studies (OKANO 1996 & WHITLEY 1998);
To demonstrate the effects on endurance performance from ingesting CHO immediately before exercise in subjects that have ingested a pre-exercise HFM.

Results
:
a High-Fat meal consumption is more favorable for endurance performance (longer time until exhaustion and higher total fat oxidation);
a High-Fat meal + maltodextrin ingestion following 3 days of "carbohydrate loading" enhances endurance running performance.
*American College of Sports Medicine; American Dietetic Association; Dietitians of Canada. Joint Position Statement: Nutrition and athletic performance. Med. Sci. Sports Exerc. 2000, 32, 2130–2145.
Conclusion: following 3 days of glycogen loading, a HFM and subsequent ingestion of a small portion of carbohydrate jelly prior to exercise enhances the performance of athlete endurance running.
This diet pattern is favorable for physical conditioning of athletes preparing for and competing in a marathon race.
Problem:

(1) The performance of prolonged, continuous, endurance exercise is limited by endogenous carbohydrate stores.
(2) The acute ingestion of exogenous substrates (carbohydrate) during exercise has little effect on the rates of glycogenolysis.

Opportunity:

Different diet-training strategies have the potential to
increase
fatty acid availability and rates of lipid oxidation, and
reduce
the rate of glycogen utilization during exercise.

Recent studies have focused on
short-term diet-training interventions that increase endogenous substrate stores
&
alter patterns of substrate utilization
(muscle glycogen and lipids) during exercise.

Example: "Fat Adaptation with carbohydrate restoration"
A dietary periodization protocol in which well-trained endurance athletes consume a high-fat, low-carbohydrate diet for up to 2 weeks while undertaking their normal training, immediately followed by the consumption of a high-carbohydrate diet and tapering off for the 3 to 1 days before a major endurance event.

Result:

A high-fat, low-carbohydrate diet intervention increases rates of whole-body and muscle fat oxidation while reducing the rate of muscle glycogenlysis during sub-maximal exercise, compared with an isoenergetic control diet. These metabolic perturbations favoring the oxidation of fat persist even in the face of restored glycogen stores and increased exogenous carbohydrate availability.
Background:

There is a consensus claiming an ergogenic effect of carbohydrates ingested in the proximity of or during a performance bout. However, in performance studies, the
protocols
that are used are often highly standardized (e.g. fasted subjects, constant exercise intensity with time-to-exhaustion test modes), and
do not necessarily reflect competitive real-life situations
. [TEMESI 2011, VANDENBOGAERDE 2011]

Strategy:
A review of 17 articles describing 22 carbohydrate interventions covering tests durations from 26 to 241 min.
Main inclusion criteria: trained subjects exercising in a postprandial state and a performance test similar to a competitive event (time-trial-like performance tests);
Excluded: fasted subjects and time-to-exhaustion tests.

Results:

Half of the carbohydrate interventions showed no performance improvement, while the other half had significant improvement between 1% and 13%.

Conclusion:

When considering only studies with a setting mimicking real-life competition, there is a
mixed general picture
about the ergogenic effect of carbohydrates ingested in the proximity of or during a performance bout with an unlikely effect with bouts up to perhaps 70 min and a possible but not compelling ergogenic effect with performance durations longer than about 70 min.
A few of the major players in de Low-Carb field: authors, proponents, ...frauds?
Drs Eades MD: experience with treating patients;
Dr. Cordain: professor-scientist @ Colorado State University (Dept. Health & Exercise Sc.), wrote over 100 peer-reviewed articles and abstracts;
Dr. Thompson MD: board certified in internal medicine and cardiology;
Dr. Westman: professor or medicine @ Duke University Health System, clinical researcher & care provider;
Dr. Phinney: a physician-scientist, has written more than 70 peer-reviewed papers and book chapters;
Dr. Volek: a professor and author, leads a research team @ the university of Connecticut;
Mark Sisson: an American fitness author and blogger, and a former distance runner, triathlete and Ironman competitor.
To quote Dr. Campbell (co-author of
The China Study
) in
The Low-Carb Fraud
(2014): "the authors of low-carb books and diets have no experience in scientific research, and generated a vast fortune by the sales of their shakes, powders, extracts, oils, bars, and even chocolates."
}
Low-Carbohydrate Nutrition & Metabolism
Am J Clin Nutr 2007;86:276 – 84.
"Recent studies (2003-2007) show that,
under conditions of carbohydrate restriction, fuel sources shift from glucose and fatty acids to fatty acids and ketones
, and that ad libitum fed carbohydrate-restricted diets lead to appetite reduction, weight loss, and improvement in surrogate markers of cardiovascular disease."
Further research
on exercising under conditions of LCDs is needed. These studies may be optimized by careful attention to the time needed for keto-adaptation, to mineral supplementation, and to the daily protein dose.
Therapeutic use
of ketogenic diets should not limit most forms of physical activity.
Diet??
Recommendations according to bodybuilding.com
... or is it?
Introduction
wholehealthsource.blogspot.com
www.bodybuilding.com
20-50 g carbs/day
energy balance
Practical Nutritional Recommendations for the Athlete?
2010
2011
2013
2011
2008
2007
late 19th century
1930s
1950-60s
1970s onwards
An experimental approach to the field of human muscle energy metabolism
Laboratory experiments: fuel sources for the contracting muscle
demonstrating clearly that lipids could be used by human skeletal muscle without first being converted to a sugar

Field studies: Polar explorers searching for the optimal diet
gave support for this notion, as it could be established that up to 60 – 70 % of the energy intake could come from fat while the subjects could maintain a high daily exercise output.
Studies responsible for most of our knowledge on sports nutrition today
Findings from these studies are currently accepted as true, but still not understood in great depth, e.g.:

carbohydrate usage is intensity-dependent
muscle training improves fat utilization and reduces lactate accumulation
"carbo­hydrate loading" elongates time to exhaustion.
Methodological improvements
E.g.: the use of isotopes, the re-introduction of the biopsy needle to take muscle biopsies, which brought about new tools for more direct measurements of both substrates used and metabolites produced by muscles.
The key role of fatty acids was recognized as was the storage and usage of muscle glycogen.
A wealth of training studies
Primary goals:
to establish the relative importance of glucose and lipids for the energy turnover;
to pin point limiting factors and the regulatory mechanisms in handling these substrates.

There is a consensus of the larger role of LIPIDS after training (but to what extent serum and/or muscle triglycerides contribute is intensely debated).

There is some debate about where the limitation is for the lipid utilization during the exercise (e.g. transport of FA into the muscle, mitochondrial FA respiratory capacity, the regulation of the FA uptake by the mitochondria).
A short history of sports nutrition
Since these early days there has been a continuous progress in our understanding of the importance of intensity, diet and training status for the substrate choice by skeletal muscle when exercising.
All available results on linking diet to performance points at
carbohydrates
being essential.

Equally clear is that a
high capacity for lipid oxidation
in the active muscles of an endurance athlete is a requirement for optimal performance. This phenomenon is only partly explained by
limited glycogen storage capacity
.

The full explanation is not really known today but worthwhile to look for as it will provide the insight needed to guide the athlete both in regard to
the ideal diet and the best training.
B. SALTIN (University of Copenhagen, Denmark), in an introduction for the Sport Nutrition conference in Birmingham in 2007, sponsored by Nestlé Nutrition & PowerBar.
Conclusion
Spreading the word
How Nestlé's Sport Nutrition Conferences communicates current research
Hansen, A. K., Fischer, C. P., Plomgaard, P., Andersen, J. L., Saltin, B., & Pedersen, B. K. (2005). Skeletal muscle adaptation: training twice every second day vs. training once daily. J Appl Physiol, 98(1), 93-99.

Hargreaves, M. (2004). Muscle glycogen and metabolic regulation. Proc Nutr Soc, 63(2), 217-220.
[HANSEN 2005] have shown that 10 weeks of training in a glycogen-depleted state resulted in an 85% greater increase in time to exhaustion compared with training with high glycogen.

These results have now been confirmed in highly trained cyclists suggesting that, regardless of the athlete’s training state, training in a glycogen-depleted state results in an increased capacity to use fat as a fuel during exercise.
Altered whole body substrate metabolism
Glycogen sparing effect during competition
Improved capacity for fat oxidation
Improved long-duration endurance performance
& improved recovery afterwards: beneficial effects on subsequent performances
(Olympics, world championships)
(triathlon, marathon, road cycling)
in a manner that stimulates the activation of cellular signaling pathways that might be involved in the muscular adaptation to training. [STEENSBERG 2002]
Glycogen depletion training @ low intensities (< 70% VO2max)
Burke LM, Hawley JA. Effects of short-term fat adaptation on metabolism and performance of prolonged exercise. Med Sci Sports Exerc 34(2002): 1492-1498.
chronic LCD
acute carbohydrate restriction through fasting
Untrained subjects undergoing a short-term (10 wk) training intervention
Conclusion: adaptation and endurance performance is augmented by lack of substrate availability
(glycogen).

‘train-low, race-high’
Well-trained subjects undergoing a 3 wk training intervention
LOW: one leg was trained twice a day, every second day in which the second training session was commenced with low glycogen content
HIGH: the contra-lateral leg trained daily under conditions of high glycogen availability every session.
self-selected power output was compromised when trained cyclists started high-intensity interval training sessions with low glycogen stores;
tracer-derived measures of fat oxidation during submaximal cycling were increased after ‘train-low’.
Hawley JA, Burke LM. Carbohydrate availability and training adaptation: effects on cell metabolism. Exerc Sport Sci Rev 2010 38: 152-60, 2010.
Yeo WK, Paton CD, Garnham AP, Burke LM, Carey AL, Hawley JA. Skeletal muscle adaptation and performance responses to once a day versus twice every second day endurance training regimens. J Appl Physiol 105: 1462-70, 2008.
lower ‘training impulse’ (max. self-selected power output)
higher resting muscle glycogen concentration, enzyme activity (CS, beta-HAD, cyt C IV)
Approach #1: altering endogenous muscle glycogen stores

[see earlier]
Subjects who commenced interval training with low muscle glycogen content had:
Approach #2: manipulating exogenous glucose availability
training after an
overnight

fast
,
prolonged training
with or without an overnight fast
withholding carbohydrate intake
during the training
session
, and/or
withholding carbohydrate during the
first hours of
recovery
.
Hawley JA, Burke LM. Carbohydrate availability and training adaptation: effects on cell metabolism. Exerc Sport Sci Rev 2010 38: 152-60, 2010.
Hawley JA, Burke LM, Phillips SM, Spriet LL. Nutritional modulation of training-induced skeletal muscle adaptations. J Appl Physiol (in press).
after 6-10 week intervention periods, a range of training-responsive metabolic markers are increased by a similar extent with or without carbohydrate supplementation.
subtle differences in muscle adaptation after reducing carbohydrate availability during training.

interactive effects on training adaptation
Collective conclusions
Manipulated variable #1: carbohydrate
different methods of training (e.g. training once-a-day versus twice every second day)
range in number of sessions & differences in recovery time between workouts
variable intervention periods
Manipulated variable #2: exercise
Are all results directly attributable to differences in CHO availability per se?
Workout portion
with
low GLYCOGEN
stores
Workout portion
with
low GLUCOSE
availability
Short-term (3-10 wk) training program
Diet intervention
Control
All workouts
with
normal or elevated
muscle GLYCOGEN
Independent of prior training status
Augmentation of training adaptation
increase the maximal activities of selected enzymes involved in carbohydrate and/or lipid metabolism
promote mitochondrial biogenesis
(diet protocol)
(training protocol)
There is no evidence of impaired adaptation
(a decline in performance outcomes)
after short-term training with low carbohydrate availability.
'train-low’
How do researchers translate dietary periodization strategies to
recommendations for coach, athlete and sports practitioner?
Changes in
selected cellular events
Mechanistic
variables being measured
Effects on isolated muscle characteristics
Changes in
training capacity
Whole body
functional
outcomes
athletic performance?
> mismatch <
NO relationship
seems unlikely...
Performance is determined by the integration
of whole body systems! Factors include:
muscle function
central nervous system workings (e.g. for pacing strategies, choice of workload or intensity following perceptions of fatigue & effort,...)
We may currently lack the appropriate tools to accurately measure exercise/sports performance (in particularly the ability to detect small changes that are worthwhile to a competitive athlete in order to change the outcomes of real world events).
Do some 'train low' strategies (i.e. training with low carbohydrate availability) have negative effects on an athlete’ s health or performance which counteract the positive effects on muscle characteristics?
You can't run on muscle alone
Is the toolbox still incomplete?
Does the bad outweigh the good?
!!
acute impairment
consequences over the long-term
"This impairment to carbohydrate metabolism would be expected to reduce high-intensity exercise performance, which is indeed the case"
complex reciprocal interactions b/w pathways of substrate utilization
up-regulating one



down-regulating others
Short-term fat-adaptation
Well-trained athletes on a 5 day high-fat diet + strenuous training regimen
robust enhancement of fat oxidation during sub-maximal exercise

NO benefits across a range of endurance exercise protocols.
Burke LM, Hawley JA. Effects of short-term fat adaptation on metabolism and performance of prolonged exercise. Med Sci Sports Exerc 34:1492-1498, 2002.
Stellingwerff T, Spriet LL, Watt MJ, Kimber NE, Hargreaves M, Hawley JA, Burke LM. Decreased PDH activation and glycogenolysis during exercise following fat adaptation with carbohydrate restoration. Am J Physiol Endocrinol Metab 290:E380-8, 2006.
Demonstrated a reduction in
the calculated rate of muscle glycogenolysis
the activity of the PDH complex
(even with CHO restoration before/maximization availability during workout)
(the rate limiting enzyme in carbohydrate metabolism)
Havemann L, et al. Fat adaptation followed by carbohydrate loading compromises high-intensity sprint performance. J Appl Physiol 100:194-202, 2006.
initial?!
decreased training stimulus
impaired muscle fibre recruitment
[Van Proeyen, et al. 2011]
reduced immune function
increased risk of illness and/or injury
???
"It may simply be the case that current studies have not been sophisticated enough to integrate various combinations and permutations of 'train low' strategies into the periodized training programs of highly-trained athletes. Perhaps 'training low' needs to be carefully integrated into parts of the complex system of training elite athletes, to allow performance benefits to be achieved in concert with the measurable cellular changes."
[Hawley, 2010]
Colombani P. Nutrition in the context of physical (in)activity and health. Nestlé Nutrition Institute, 2010.
[ref: WHO, FAO. Diet, nutrition and the prevention of chronic diseases. Geneva, 2003.]

Several
nutritional recommendations
have been delivered for such a long time that one could easily define them general knowledge. Among these, we have the limitation of total fat intake to about 30 EN%, of saturated fatty acids to not more than 10 EN%, (...)

Before the emergence of Evidence-Based Medicine, and correspondingly of Evidence-Based Nutrition, general recommendations were very often derived
merely from expert consultations
, which often do not rely on systematic assessments of the scientific literature.

A paradigm shift
While by no means a novel nutritional ergogenic, carbohydrate loading (or ‘glycogen supercompensation’) remains the foundation of nutritional preparation for optimal performance in endurance sports and, to a large extent, should underpin all other race day nutritional practices.

The dietary-exercise protocols recommended for carbohydrate loading and the subsequent effects on metabolism and exercise capacity have been reviewed elsewhere [Hawley et al. 1997].

Glycogen supercompensation improves endurance performance (in which a set distance is covered as quickly as possible) by 2 to 3%.

Why recommend Low-Carb to athletes?
Low-carb diets on the shelves
How does the athlete benefit from dietary fat?
Fueling tactics that emphasize CHO-based diets and sugar-based supplements bias your metabolism towards carbohydrate while simultaneously inhibiting fat mobilization and utilization, lasting for days after CHO consumption. This becomes problematic during prolonged exercise when body CHO sources (i.e. muscle & liver glycogen) are exhausted.

The transition from sugar to fat burning - turning blood glucose & muscle glycogen into secondary fuels - allows you to train harder, perform longer and recover faster.

A growing body of literature now points to the merits of reducing dietary carbohydrate to optimize fat metabolism (cf. selection of trials)

A decade of human research on diets lower in carbohydrate, and physiological adaptation to such diets, have shown:
<-> current majority opinion & sport nutrition "group think"
"a HCD locks a person into a
dependence
on carbohydrate as the dominant fuel for exercise"

"You can train your body to burn fat by
simply
changing your diet over a period of a few weeks"

"This strategy has
worked
for us and many people we know (...) we have conducted human research supporting this approach"
Shifting the High-Carb paradigm
Introducing: the keto-adapted state
In order to
sustain
a high level of performance under conditions of glycogen depletion and decreased glucose availability,
cells must adapt
to using fat fuels.
Previously held
beliefs
about the optimum diet for athletes need to be reconsidered in the context of
data
obtained after keto-adaptation.
Keto-adaptation has the potential to
improve
human performance and recovery. This strategy allows rapid mobilization and utilization of “non-carbohydrate” lipid fuel sources. Keto-adapted athletes show marked increases in fat burning, indicating that
peak rates
of human fat oxidation have been significantly underestimated.
Understanding how to use CHO to optimize metabolic response to physical activity
Developing nutritional approaches to prevent fatigue and improve exercise tolerance
Focussing on ways to enhance glycogen levels and CHO oxidation: carbo-loading, multiple sugar sources, etc.
methods to decrease?
confirmation bias!
carbs are... an obligate component




an optional nutrient in an endurance athlete's diet
if you're consuming lots of them, but given the time to adapt,
they can be reduced to...
The 65% VO2max threshold
Exercise intensity is a determining factor for the proportion of fat used as fuel.

There is a specific intensity where fat burning peaks -- exercise at higher intensities increasingly depends on glucose (blood) & glycogen (muscle)
(in a moderate to high-carb diet)
an intensity most endurance athletes can easily maintain for several hours
Is it justified to teach away from low-carb/high-fat diets for these athletes?
the "switch" is not a gradual process but a coordinated set of metabolic events
in a keto-adapted athlete, specific mechanisms allow for significantly
higher rates of peak fat oxidation at higher exercise intensities
the minimum time for keto-adaptation to occur has been largely ignored in metabolic studies on the effect of high-fat diets on endurance performance (cfr. trial overview: 2 weeks or less!)
the authors published studies of 4 to 6 weeks demonstrating a
progressively increased capacity to mobilize and oxidize fat at the 65% VO2max threshold
Phinney SD, et al: The human metabolic response to chronic ketosis without caloric restriction: preservation of submaximal exercise capability with reduced carbohydrate oxidation. Metabolism 1983, 32(8):769-776.
"ketone body": lipid-based fuel source
when carbs are restricted (esp. brain)
Carb-rich diets are are vigorously promoted to endurance athtes, b/c maintaining a high muscle glycogen level is essential to achieve optimal performance.
less oxidative stress during exercise and more rapid recovery during exercise sessions
greater reliance on body fat at rest AND during exercise, meaning less dependence on glycogen and less need to carbo-(re)load
accelerated use of saturated fatty acids for fuel, allowing for a risk-fee high saturated fat intake
the practical possibility of effective training with desirable changes in body composition and body-to-weight ratios
neither required nor desired for many athletes!
short-term studies comparing LCM vs. HCM using brief periods of intense exercise argue the superiority of a high-carbohydrate diet

recent
research data
supports the conclusion that using a > 2 week adaptation period for a well-formulated LCD, humans can deliver equal or better endurance performance compared to the best HCD strategy






observational evidence
of ultra-endurance athletes performing at consistently high levels using varying degrees of CHO-restriction to optimize fat burning
how to optimize
fat oxidation
in athletes
benefits of
keto-adaptation
on exercise performance
significant progress in understanding &
a number of nutritional strategies aimed at increasing fat burning during exercise
caffeine, carnitine, ephedra, MCT oils, green tea extract, hydroxycitric acid, ...
[by S. Phinney]
Keto-adaptation experiments
Phinney's
in endurance athletes
Phinney SD, et al. The human metabolic response to chronic ketosis without caloric restriction: preservation of submaximal exercise capability with reduced carbohydrate oxidation. Metabolism 1983, 32(8):769-776.
Venables MC, et al. Determinants of fat oxidation during exercise in healthy men and women: a cross-sectional study. J Appl Physiol 2005, 98(1):160-167.
Highly trained cyclists performed an endurance test to exhaustion on their usual HCD & again after being fed a VLCD (>80en% fat, <10 g CHO) for 4 weeks
a complete preservation of endurance performance after 4 weeks on a diet that contained virtually no carbohydrate
a dramatic shift in metabolic fuel from a heavy dependence on carbohydrate to nearly complete reliance on fat in the keto-adapted cyclists
On average keto-adaptation in Phinney et al. (1983) resulted in peak fat oxidation rates of 90 g fat/hour – 50% greater than the highest recorded value for any participant in Venables et al. (2005)
"These highly
trained athletes
, who already had very high fat oxidation rates, were able to dramatically increase them further – not by changing their training, but
by changing their diet
. It is apparent that a
low carbohydrate diet
that allows you to optimally access your
fat stores
and increases mitochondrial
fat oxidation
is a fully rational approach."
provides a steady and sustained source of fuel for the brain
may improve insulin sensitivity and recovery from exercise
spares protein from oxidation, preserving lean tissue
decreases lactate accumulation
How to fatten up your diet
Implementing a well-developed
keto-adaptation diet plan
Carbohydrate
Can athletes actually maintain a diet high in fat and low in carbohydrate for extended periods of time?
Fat
Key to successful keto-adaptation is figuring out ways to specifically increase fat intake without over-consuming carbohydrate and protein

Emphasize the fuel sources the body prefers to burn



Limit foods with a high proportion of the vegetable (n-6) polyunsaturates, with a balanced intake of n-6 and n-3 fats
Protein
"enough": DRI values - developed for the average weight stable, unstressed individual - are inadequate during weight loss, physical or emotional stress
"not too much": extra amino acids from protein over-consumption can be converted to glucose, raising insulin levels, suppressing fat burning.

Focus on small to moderate portions of meat (or other protein foods) and combine them with generous portions of good sources of fat
This carb-restriction level (<50g CHO/day) is safe, sustainable, and satisfying
An appealing variety of meals can be consumed even at this low level
Fast-digesting carbohydrates such as commonly recommended after exercise are counter-productive in the keto-adapted state.
NO "carbage" (ketone-suppressing carb-dense foods):
e.g. cereals, breads, pasta, potatoes, pastry, candy, juices
meat, hard cheeses & cream
vegetables @ every meal
< 2 oz./day: nuts & seeds
< 100g/day: berries, avocados, olives, tomatoes
(A guide on how to restrict)
is necessary, in moderation
your most important fuel
"The widespread belief that dietary saturated fat is harmful turns out to be an out-dated paradigm. A low-carb, high-fat diet has been recently shown to significantly decrease circulating levels of (serum) saturated fat."
Forsythe CE, Phinney SD, et al. Comparison of low fat and low carbohydrate diets on circulating fatty acid composition and markers of inflammation. Lipids 2008, 43(1):65-77.

Forsythe CE, Phinney SD, et al: Limited effect of dietary saturated fat on plasma saturated fat in the context of a low carbohydrate diet. Lipids 2010, 45(10):947-962.


olive, canola, high oleic safflower, coconut & palm oils, butter, tallow, lard;
meat, eggs, olives, avocados, heavy cream, sour cream, nuts, seeds, cheese;
salmon, tuna, sardines, herring & other cold water fish.
= Foods containing mostly mono-unsaturated and saturated fats
This is why I am and plan to remain a low-carb athlete:

1. I can easily remain weight stable.
2. I breathe slower when exercising.
3. I don’t need to eat even during long exercise.
4. I need less water during long exercise.
5. I recover faster and have less post-exercise pain.
6. My performance is equal to or better than when carb-fueled.
7. My general health is better.
8. I can exercise for several hours at a high level of effort without bonking.
David Dreyfuss — Observations of an Older Low-Carb Recreational Athlete
Diet-training strategies in real life?
Reviewing the scientific evidence for the hypothesis that
training undertaken with low carbohydrate availability promotes endurance-training adaptation
to a greater extent than when training undertaken is with high carbohydrate availability.
Carbohydrate loading - glycogen supercompensation
clinicaltrials.gov
sports drinks
Multiple
transportable
carbohydrates
A thematic review suggesting carbohydrate restriction as a promising nutritional approach to overcome the epidemic of obesity and type 2 diabetes.
Anecdotal "evidence"
[COSTILL 1977]
According to research between 1997-2007:
MACRO-
Cox GR, Burke LM, et al. Daily training with high carbohydrate availability increases exogenous carbohydrate oxidation during endurance cycling. J Appl Physiol 109: 126–134, 2010.
Subjects: 8 M long-distance athletes (trained)
Discussion
Previous studies investigating the effects of a high-fat diet on exercise metabolism have consistently used
isocaloric fat-rich diets
. The implication of this is that increased dietary fat intake may be compensated by reduced energy intake from carbohydrate.
Van Proeyen et al. Training in the fasted state improves glucose tolerance during fat-rich diet. in: J Physiol 588.21 (2010): 4289–4302.
Follow-up
Mechanisms of the Effect of Physical Activity on the Adaptation to a High-Fat Diet (Pennington Biomedical Research Center)
It has been shown that high level of physical activity can accelerate the adaptation to a high fat diet by increasing fat oxidation. In this study we will determine the mechanism involved in this adjustment.

Our hypotheses are:
High fat diets
decrease skeletal muscle glucose metabolism
and decrease mitochondrial biogenesis
A high fat diet will increase hepatic and
skeletal muscle lipid
Increased physical activity will prevent both these deleterious effects
How to overcome methodological differences?
[cfr. multiple studies on diet patterns and meal frequency of elite endurance athletes, e.g. BURKE 2003 Int J Sport Nutr Exerc Metab 13]
Translating Sports Science Research to Practice in the Field
Sports practice is radically different from a laboratory-based intervention. Indeed, the measurement of sports performance is a highly challenging area, with most scientific investigations being unable to detect the changes or differences in performance that would be worthwhile in the world of competitive sport, where millimeters and milliseconds can separate the winners from the rest of the field.

Enhanced access to scientific reports, via media such as
PubMed or sports science websites and blogs
, means that there is rapid communication of ‘breakthrough’ studies of nutrition and exercise interaction to sports scientists, coaches and athletes themselves. All these factors interact to create enthusiasm in the sports world for the results of diet-exercise studies, but they can also make it
difficult to find a direct application of the results to the athlete.

The final analysis will require consideration of the practicality or logistics of the intervention:
can the athlete afford it
is it accessible and available
does it integrate with the athlete’s other nutritional goals
is it safe and ethical
...

Understandably, this ‘ideal world’ is too intricate to be realistic. Therefore, the translation of most sports science research into practice relies mostly on interpolation and extrapolation of the available studies as well as individual
experimentation in the field
.
1997-...
2002-2006
Conclusions
: in endurance exercise, a hypercaloric High-Fat diet:
elevates IMCL content
increases the contribution of IMCL to energy provision
stimulates exercise-induced IMCL breakdown
does not impair exercise-induced muscle glycogen breakdown;
provides adequate amounts of dietary CHO
to maintain high muscle glycogen content during training
(i.e. prevent a training-induced glycogen drop).
http://www.ext.colostate.edu
A recap of key concepts
Fat and carbohydrate have a reciprocal relationship as substrates for exercise.
A well-known adaptation to training is to increase the capacity for fat utilization
Athletes should consider strategies other than training that might further enhance fat use during exercise.
an increased use of fat to sustain low-moderate intensity exercise may spare glycogen as a substrate
Potential opportunities include: acutely increasing FFA concentrations during exercise, or chronic strategies to increase muscle capacity for fat oxidation
Increasing the plasma concentrations of FFAs and their delivery to the muscle can be achieved by fasting or restricted carbohydrate intake, as well as by high-fat meals) before exercise
Longer term exposure to a high-fat, low-carbohydrate diet has been shown to cause chronic adaptations in the muscle to increase its capacity for fat oxidation
The majority of studies have reported no benefits to exercise endurance or performance, and a longer term study (7 week) actually found a compromised adaptation to the training process
Because the ability to train at high intensities is impaired by a low-carbohydrate diet, and for general health concerns, long-term exposure to a high-fat diet is not recommended to athletes.
Instead, the concept of dietary periodization has been proposed, involving rapid adaptation to a high-fat diet followed by carbohydrate loading and carbohydrate feeding during exercise; this offers the potential benefits of the combination of high carbohydrate availability with spared use.
The practical implication of the finding of impaired rather than spared glycogen use is a reduction in performance of high-intensity bouts
This is likely to be of major practical importance in the world of sport in which the decisive moments in even ultra-endurance events lasting many hours involve high-intensity activities.


There appears to be a sophisticated reciprocal relationship between fat and carbohydrate utilization during exercise that can be manipulated to show interesting outcomes in terms of exercise metabolism. However, the practical outcomes do not favor performance benefits and may even impair critical aspects of sports performance.
In summary
Burke LM, et al. Effect of
fat adaptation
and carbohydrate restoration on metabolism and performance during prolonged cycling. J Appl Physiol 89: 2413–2421, 2000.
Carey AL, et al. Effects of fat adaptation and carbohydrate restoration on prolonged endurance exercise. J Appl Physiol 91: 115–122, 2001.
Stepto NKCA, et al. Effect of short-term fat adaptation on high-intensity training. Med Sci Sports Exerc 34: 449 – 455, 2002.
Burke LM, et al. Adaptations to short-term high-fat diet persist during exercise despite high carbohydrate availability. Med Sci Sports Exerc 34: 83–91, 2002.
Cameron-Smith D, et al. A short-term, high-fat diet up-regulates lipid metabolism and gene expression in human skeletal muscle. Am J Clin Nutr 77: 313–318, 2003.
Stellingwerff T, et al. Decreased PDH activation and glycogenolysis during exercise following fat adaptation with carbohydrate restoration. Am J Physiol Endocrinol Metab 290: E380 –E388, 2006.
De Bock K et al. "Type-specific muscle glycogen sparing due to carbohydrate intake before and during exercise." in: J Appl Physiol 102 (2007): 183–188.
Van Proeyen et al. Training in the fasted state improves glucose tolerance during fat-rich diet. in: J Physiol 588.21 (2010): 4289–4302.
Burke LM, Hawley JA. Effects of short-term fat adaptation on metabolism and performance of prolonged exercise. Med Sci Sports Exerc 34:1492-1498, 2002.
Stellingwerff T, Spriet LL, Watt MJ, Kimber NE, Hargreaves M, Hawley JA, Burke LM. Decreased PDH activation and glycogenolysis during exercise following fat adaptation with carbohydrate restoration. Am J Physiol Endocrinol Metab 290:E380-8, 2006.
Havemann L, et al. Fat adaptation followed by carbohydrate loading compromises high-intensity sprint performance. J Appl Physiol 100:194-202, 2006.
Yeo WK et al. Fat adaptation followed by carbohydrate restoration increases AMPK activity in skeletal muscle from trained humans. J Appl Physiol 105 (2008): 1519–1526.
Larson-Meyer E, et al. Effect of Dietary Fat on Serum and Intramyocellular Lipids & Running Performance. Med Sci Sports Exerc. 2008;40(5): 892-902.
Hansen AK, et al. Skeletal muscle adaptation: training twice every second day vs. training once daily. J Appl Physiol. 2005;98(1):93-9.
Yeo WK, Burke LM, Hawley JA, et al. Skeletal muscle adaptation and performance responses to once a day versus twice every second day endurance training regimens. J Appl Physiol. 2008; 105(5):1519-26.
Hulston C, Jeukendrup AE, et al. Training with low muscle glycogen enhances fat metabolism in well-trained cyclists. Medicine & Science in sports & exercise 42/11 (2010): 2046-2055.
Van Proeyen K, Hesselink M, et al. High-fat diet overrules the effects of training on fiber-specific intramyocellular lipid utilization during exercise.
In: J Appl Physiol 111 (2011): 108–116.
Murakami I, et al. Significant Effect of a Pre-Exercise High-Fat Meal after a 3-day High-Carbohydrate Diet on Endurance Performance.
Nutrients 2012, 4, 625-637.
Cox GR, Burke LM, et al. Daily training with high carbohydrate availability increases exogenous carbohydrate oxidation during endurance cycling. J Appl Physiol 109: 126–134, 2010.
Achten J, Jeukendrup AE, et al. Higher dietary CHO content during intensified running training results in better maintenance of performance and mood state. J Appl Physiol 96 (2004): 1331–1340.
Colombani et al.
Carbohydrates
and exercise performance in non-fasted athletes: A
systematic review
of studies mimicking real-life. Nutrition Journal 2013, 12:16.
Yeo WK, Hawley JA, et al. Fat adaptation in well-trained athletes: effects on cell metabolism. Appl. Physiol. Nutr. Metab. 36: 12–22 (2011)

http://www.nestlenutrition-institute.org/Resources/Library/Free/workshop/booknniw69/Pages/SportsNutritionMoreThanJustCalories
http://www.nutritionandmetabolism.com/
http://www.artandscienceoflowcarb.com/
Bibliography
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