A scientist’s dilemma

I would like to consider myself a scientist – or at the very least a man of science. I do science for a living, although admittedly I don’t actually know what science is.

When I talk to people about nutrition, whether in person or in front of a class, I make an attempt at presenting nutrition from what I believe to be a scientific standpoint.
But there invariably comes a point during my rambling monologues when the listeners who aren’t sleeping realize that my advice on nutrition is roughly the opposite of what everybody else say, the opposite of what their textbooks says and the opposite of what the government recommends.

Eat fat,” I say, “preferably saturated fat. Butter is great. Avoid sugar and eat proteins. In fact, just make sure that most of what you are eating was also once eating something. Don’t eat grains, at least no wheat. If you don’t like seafood you might want to supplement with omega 3.” You get the picture.

At this point, a hovering hand usually catches my attention.

Are you telling us the government is wrong?

Yes, that is correct,” I think to myself. But I don’t say it.

Instead I try my best at working around question and feeling very much like a greased up politician I effectively avoid the question by saying something about how scientific results are often disagreed upon, how it takes time to change scientific paradigms, how textbooks are slowly updated, how science is not immune to the ways of money and how even scientists rarely admit to being wrong even though the evidence calls for it.

But, what I would like to say is, “Yes, that is correct.” In fact, what I would like to say that it is hard to be more wrong than the official guidelines.

I dodge the question, because I know I will lose credibility by asserting myself. Claiming to possess a knowledge that has escaped most everybody but me will drive my audience away and luckily so. It is after all a sign of healthy skepticism in my audience.

If I succeed in getting across the message that even the government might get it wrong, there invariably is a follow-up question.

Who then should we listen to?”

Me,” I think.

But I don’t say it.

Instead I talk about how, if you really want to know the truth, if you really want to know about nutrition and health, you have to read. You have to read and study and accumulate your own knowledge. Only then can you make sensible decisions about whom to listen to.

If however, you don’t want to spend your time learning about nutrition and navigating the maze of confusing information, you’ve got three more or less sensible choices:

1. You can trust your experience and the experience of those around you. A lot can be learned from listening to the body, cleaning out the senses and having a keen eye for the obvious. Humans however, are prone to deceiving themselves.

2. Find any random person or organization that promote a dietary strategy and follow it. This strategy is commonly used in religion and judging by the number of religious people around, I would say it’s an easily followable approach.

3. Don’t give a crap and eat whatever you want to eat.

I hate that there are no better options. When asked about whom to trust I would like to give people a name. Preferably the government, as it should be their responsibility to make correct and important knowledge available to the public. But I can’t give a name. In truth, the only option for those who really seek the truth is to find it themselves.

And how bloody ineffective it all is. But as I claim that those who should be trusted can’t be trusted there is no way people will or should blindly trust me.

And who’s to blame for this sticky situation? Much of the blame lies with scientists; the very group of people I would like to consider myself a part of.

Scientists have disagreed far more than the evidence permits. They have been led by money, fame and feelings and are in general guilty of being just like ordinary humans.

I do not think nor hope that the day comes when I can teach a nutrition- and health approach that everybody agrees upon. After all, the progress of science rests entirely on disagreement. But it should be possible to agree about the important issues. It is possible, but agreement honors us with its absence. And in the meantime everything is so much more difficult than it has to be and the obvious question poses a dilemma where there should be none.

Exercise Zen

When I’m in this state everything is pure, vividly clear. I’m in a cocoon of concentration. And if I can put myself into that cocoon, I’m invincible. . . . I’m living fully in the present. I’m absolutely engaged, involved in what I’m doing. . . . It comes and it goes, and the pure fact that you are out on the first tee of a tournament and say, «I must concentrate today,» is no good. It won’t work.

Tony Jacklin 

For a good proportion of us humans, our body is nothing more than a way of getting the brain from A to B. We have become a brain transporter tool – a way of moving the “ego” around. Although this does not necessarily strike everybody as problematic, It very well can be.

It can limit our happiness.


Not because you have to have a magazine cover body and put down miles on the treadmill to be happy.

I do not wish to be considered as one of those hyperactive, overly positive, too good looking individuals, often observed at any local gym, that truly believe they can change the world by getting everybody to exercise more and eating healthy. I don’t want everybody to be fit or thin – what a horrible thought and what a depressingly boring world it would be.

But, I would like people to be able to get the information they want and need so that they can do what they want with their bodies and their lives.

The reason why the body becoming a brain carrying tool can be problematic, is because the mind and the body are impossible to differentiate. It is problematic to talk of them as two separate things as it is equally problematic to consider them to be one (René Decartes is much to blame for our dualistic view of ourselves).

Just as our thoughts and feelings affect the functions of our body and the bodily milieu, our body greatly affects our thoughts, feelings and personality.

Our oversized human brain and the concomitant great ability to imagine situations, to plan ahead and to consider multiple situations and outcomes can be a curse. For example, I can sit in quiet surroundings with a body at rest and still have an overactive mind. Because I can picture possible future outcomes, I can stress myself silly and sick while being totally at rest. Adrenaline and cortisol can go up.  My heart is beating faster and stronger, I start sweating and breathing heavily, all while sitting perfectly still.

Most tragic of all is that I can make my body respond like this by thinking of things to come that most likely will never happen. Let’s face it, as humans we are great at considering multiple future situations, but not necessarily any better at predicting the actual future to be. How often does a situation turn out to be exactly how you pictured it would be?

This stress can gradually destroy my body from the inside out. My cells function more poorly and are broken down to a greater degree. Stress is a catabolic state. While sitting perfectly still and wrenching my mind I am effectively weakening my own body.

We do not need to have a higher than normal heart rate to be stressed. Feeling bad is also stress. Depression seems to be as deteriorating as anxiety. Over time, feeling bad can reduce a body to ruins.

As negative thought patterns is detrimental to the body, a poor physical health and poorly functioning body can be detrimental to the mind. Luckily for us, both the body and the mind are ours to mold. Neither is unchangeable.

There are many reasons why being physically active can improve our mental health and well being. The secreting of hormones that increase our well being is one effect. A more effective vasculature, improved transportation potential and even the forming of new cells are other. There is also an anthropologic aspect worth considering. As humans, our bodies are made for (have involved into) activity and unless the body are given the stimuli it is made for, we will feel unfulfilled.

Last but not least, physical activity or exercise can give our minds much needed rest. Exercise is distraction for the mind.

While it is easy to fill the mind with multiple thoughts and feelings at rest, it is much harder to concentrate on multiple things while being active.

One of the greatest ways of giving the mind a rest is by giving the body the opposite. Once you step on a treadmill, jump on bike, go for a run/swim/walk or whatever, the body takes over. While intensity is gradually increasing, while the muscles work harder and harder, while you sweat more and the heart beats faster, there is no longer room for thoughts and feelings.

The body forces the mind to focus on one thing. The head is no longer filled with thoughts about annoying colleagues, what to eat for dinner, how to get a job, how to pay the loan or what to do with your life. The exercise forces the mind to let go of all of this and to simply focus.

Although I admittedly spend most of my time sitting on my ass, I do go out for the occasional exercise. In particular, I like jumping. I like landing too, but not nearly as much as I like jumping.

The wonderful thing about jumping is that it freaks the hell out my mind. The higher the fall and the bigger the challenge, the less my mind is involved. It is uninvolved not because of panic or fear, but because there is no room for thoughts. A difficult physical situation requires my body to do what it does best. To react to stimuli and to adjust quickly. There is no time for thinking.

Photo: Jon Lucas 

This feeling is independent of activity type. Some people report that they get lost in the activity during a spinning class. With pounding hypnotic music, heart racing and lungs screaming they let the body take over and they become the cycling. You can lose your self in your Grok workout or when going for a quick walk.

A Japanese Zen Buddhist would probably call this “Mushin”- simply translated; “no mind.” A sport psychologist would probably call it flow or possibly runners high.

No matter the name it is given, giving the mind a break while making the body a little more fit is a wonderful experience – an experience in which, even for just a second, the line between the body and the activity is eliminated. Making a distinction between myself and the activity no longer make any sense. In this state I am the jump.

In fact, some of my most peaceful moments are in situations where my heart is racing and my muscles aching.

If one puts his mind in the action of his opponent’s body, his mind will be taken by the action of his opponent’s body.
If he puts his mind in his opponent’s sword, his mind will be taken by that sword.
If he puts his mind in thoughts of his opponent’s intention to strike him, his mind will be taken by thoughts of his opponent’s intention to strike him.
If he puts his mind in his own sword, his mind will be taken by his own sword.
If he puts his mind in his own intention of not being struck, his mind will be taken by his intention of not being struck.
If he puts his mind in the other man’s stance, his mind will be taken by the other man’s stance.
What this means is that there is no place to put the mind.

Takuan Soho

High fat diets and endurance exercise performance

«When first thrown wholly upon a diet of reindeer meat, it seems inadequate to properly nourish the system, and there is an apparent weakness and inability to perform severe exertive fatiguing journeys. But this soon passes away in the course of two or three weeks.«

The above excerpt is from the journal of Lt. Frederick Schwatka who covered over 3000 miles on foot over ice, snow and tundra, along with 17 other expedition members and 44 dogs, returning to Hudson’s Bay in March of 1880. Once the initial provisions were depleted, the expedition’s only source of food was hunting and fishing.

Many people go low carb/high fat for better health and vitality and at the same time exercise quite a lot. There is little to indicate that recreational physical activity performance is impaired by low carbohydrate feeding. However, the case for low carb/high fat diets for competition exercise is somewhat different.

There are highly skilled sportsmen who admit to following a low carbohydrate lifestyle who still perform world class.

In the recent 2010 Winter Olympics, Swedish biathlon performer Bjørn Ferry won the gold medal in12.5km pursuit. Ferry proclaimed following the gold medal that he would celebrate with some champagne and cream. He is known for following a low carb diet strategy.

Fellow countryman and triathlon world champion Jonas Colting, was quoted in Swedish Runners World saying the carbohydrate supremacy is a brainwashing scheme that would have made George Orwell proud. He also explained that;

Not until the mid 90’s when I came in contact with foreign influences and new findings did I make changes that so far have produced four European and World Championship medals and two victories in the Ultraman World Championship.

Colting follows the “train low-race high” principle where high carbohydrate intake is reserved for the immediate time around competition.

There are many athletes who follow a more or less strict low carb dietary regimen with great success. However the scientific data to support this strategy is actually poor and close to non-existing.

During the 80s and 90s and up until a few years ago there was a big interest in examining diets with different macronutrient composition as a means to enhance exercise performance. High fat diet (HFD) studies seem to have been especially popular during the nineties up until about 4 years ago, when the interest subsided. The declined interest came after several reviews concluded that high fat diets did not enhance performance and sometimes even caused a decreased performance and suboptimal adaptations to exercise. The foundation for these conclusions was poor. The fact is that there is a lack of well controlled longitudinal studies to conclude either way.

The theory 
In theory the performance enhancing effect of high fat diets is simple. Our body is fueled by two sources: food and stored energy. During exercise food is not an option so the required energy must be supplied by energy stores. These stores are either carbohydrate stored as glycogen in liver and muscles or fat stored in fat tissue and muscles. The amount of energy stored as glycogen isn’t really that much and after a brief bout of exercise the stores are emptied. The normal muscle glycogen stores of well trained athletes are generally sufficient to fuel activities up to 60–90 min.

If we eat carbohydrate rich diets the body will get most of its energy from glycogen during exercise. If we on the other hand eat high fat the body will get a greater proportion of its needed fuel from fat.

Moreover, the point of fatigue during exercise closely correlates with the reduction of glycogen stores beneath a certain point. If however we can make the body use fat as the primary energy source during exercise, glycogen can be spared and performance increased. The energy stored as fat also does not get depleted and so is not a limiting factor.

The amount of glycogen stored in muscles are often estimated to be 300-900g and the amount in the liver about 80-100g.

Although glycogen obviously is a short term energy source, the reliance on glycogen and carbohydrate for fuel is the norm in most forms of exercise. When exercise duration increases athletes simply keep consuming carbs during exercise and competition to keep glycogen stores from depleting.

Many of us who have been involved in sports for some time are familiar with the concept of carbohydrate loading. It has been a part of sports literature from 1939. The concept stems from the1920 data of Krogh and Lindhard, who build themselves a homemade chamber where they were able to measure how different diets caused different respiratory exchange ratio (RER).

The carb for sports supremacy came about following a 1939 study by Christensen and Hansen who did a crossover study with a low carb diet, a moderate carb diet and a high carb diet, each for a period of 1week. After each diet, time to exhaustion was measured on an ergometer bike. Compared to the low carb time of 81min the subjects cycled for 206min on the high carb diet.

Since then, the consensus has been to feed athletes large amounts of carbohydrates to fill glycogen stores to the max, and this is still the norm. Close to everything about exercise performance and diet has been about trying to increase glycogen stores, because glycogen depletions and fatigue coincide. Athletes are commonly recommended a diet of 60 – 70% carbohydrate for optimal performance. In addition, during prolonged activity it is common to consume large amounts of sugary beverages to stock up on carbs.

Last, but not least there is an important physiological mechanism behind the whole “carbs for competition.” Unlike carbohydrates, fat cannot be oxidized under anaerobic conditions. This means that as soon as we reach high intensities, as we commonly do during competition speeds, carbohydrates has to be our primary energy source.

As seen in the above figure, carbohydrates are the main fuel source during high intensities while fat dominates at lower intensities. When exercise intensity increases the body cannot take up and supply sufficient oxygen to support the oxidation of fat. During prolonged low intensity activity the blood flow in the adipose tissue increase. This increases the rate of fat delivery from fat tissue. During high intensity exercise sympathetic vasoconstriction decrease adipose tissue blood flow, fatty acids accumulate in the fat tissue and the amount of fat transported to muscles decrease. This also contributes to the low fat oxidation rates at high intensities.

I know this last bit seems a crucial point. No competition exercise is performed at low “fat burning” intensities. Even in marathons or triathlons intensities goes up and down and an athlete need the ability to sprint or to rely on glycogen for shorter periods of time. But maximal fat oxidation rates differ immensely and in some fat oxidation is not suppressed until intensities reach well above 80% VO2max.

Muscle glycogen and plasma glucose can contribute 130kJ of energy per min (32kcal/min) during high intensities. Fat is more slowly used and can supply in the area of 6-7kcal/min. The carbohydrate stores are quickly depleted during prolonged high intensity exercise, but the stores are also quickly refilled when carbohydrates are eaten.

In the end carbohydrates can supply more energy per time unit. It can supply energy even at high intensities, but the depletion of glycogen is when exhaustion sets. Fat on the other hand is burned slowly. It cannot supply energy during high intensities, and eating a high fat diet may lead to smaller glycogen stores. However, the amount of fat stored is never a limiting factor for performance.

I’ll admit that, based on the above, the case for going high fat is not strong. But there is still hope. The rules governing the human metabolism are not set in stone. They can be bent and stretched to better suit our needs. The body is adaptable, very adaptable.

Adaptation to high fat eating and maximal fat oxidation
A chronic high fat diet cause a marked shift in substrate use compared to high carbohydrate diets. Interestingly, the adaption in substrate use caused by high carbohydrate intake is close to instantaneous, whereas the adaptation to a high fat diet can take weeks.

In addition, the adaptation persists for some time after carbohydrate intake is increased and glycogen stores refilled. It is possible to maintain an increased fat oxidation while having full glycogen stores. This strategy, though similar to carbohydrate loading is actually more of a fat loading and very much like the “train low-race high” principle.

When we start eating high fat we gradually get better and better at burning fat. If we are well trained, we also burn more fat at higher intensities. Fat is released faster and in greater amounts from the fat tissue, it is also transported faster into the muscles and the mitochondria. The muscles also store more energy as fat and get better at using this fuel as well. Full adaptation takes time tough, and it is likely that optimal adaptation need >4 weeks. High fat diets cause a shift in the expression of our genes into coding for several of proteins involved in fat metabolism.

After adapted to high fat diets we can oxidize more fat during exercise and we get a higher maximal fat oxidation. Endurance trained athletes are particularly adept at burning fat. An endurance athlete adapted to a high fat diet is a fat burning machine. Still, endurance trained athletes are not a homogenous group and may differ greatly in their fat burning capacity.

Achten and Jeukendrup tested 55 endurance trained athletes to find maximal fat oxidation and at what level of intensity it occurred. Maximal fat oxidation averaged 0,52g/min at an intensity level of 63% VO2max. But there were large variations in both maximal fat oxidation and the rate of fat oxidation. Although the average intensity for maximal fat oxidation was at 63% VO2max some athletes cycled at more than 85% VO2max before fat oxidation declined, while in others it went downhill when reaching 50% VO2max. This study used a high carb diet and the exercise was performed after an overnight fast.

Knechtle and coworkers found a higher fat oxidation at 75% VO2max than at 65% and 55% VO2max for both men and women and in both running and cycling. This intensity was related to the lactate threshold for both sexes in cycling.

Achten and Jeukendrup also showed that the first increase in lactate coincided with maximal fat oxidation.

Studies of HFD and performance
Venkatraman et al (2001) examined the effects of increasing dietary fat on endurance exercise as measured at 80% VO2max. 14 trained runners serially consumed a 15% fat diet, a 30% fat diet and 40% fat diets for four weeks each. In the last week of each diet period the subjects ran to exhaustion at 80% of their VO2max. On the 15% diet, the women ran 39.2 min. and the men ran 44.3 min. Increasing dietary fat to 30% significantly increased the running time to exhaustion by 19% for women (46.6 min) and 24% for men (54.9 min). Increasing the dietary fat to 40% did not significantly increase endurance time, compared to the 30% diet.

30% fat is not a high fat diet, but the results mirror many similar studies that indicate a negative effect of reducing fat to below “normal” levels. For example, in 2000 Horvath et al examined 12 male and 13 female runners who ate diets providing 16% and 31% fat for four weeks. In addition, six men and six women increased their fat intakes to 44%. Endurance and VO2max were tested at the end of each diet period. Although the diets were designed to be isocaloric the runners on the low fat diet ate 19% fewer calories than on the medium or high fat diets. The endurance test was a run to exhaustion at 80% VO2max.

The table below shows the timed run to exhaustion after the different diets.

From Horvath et al 2000

The endurance time to exhaustion in the subjects on the medium fat diet increased 20% in females and 8% in males compared to the low fat diet.

Muio et al (1994) examined the effects of dietary manipulations on six trained runners. The runners were given diets of 38%, 24% and 15% fat each for 7 days. Running time to exhaustion at 75- 85 % VO2max was greatest after the 38% diet with 91.2min as compared with the 15% diet with 75.8min and the 24% diet with 69.3min. VO2max was also higher on the 38% diet. The results imply that restriction of dietary fat may be detrimental to endurance performance.

A much quoted study is one from Stephen D. Phinney from 1983. He put 5 endurance trained athletes on a ketogenic (85% fat) diet for 4 weeks. After the diet period the athletes did not have a significant reduced performance on a 150min test at 62-64% VO2max, and the results almost seemed to point to an advantage. However, four of the cyclists showed little change while one participant had an almost abnormally large improvement. It is difficult to say if this improvement was caused by diet or whether this athlete just had a very good day.

In 1999 Silvia Pogliaghi and Arsenio Veicsteinas had fourteen untrained men sequentially submitted to 4 weeks eucaloric diets (30%, 15%, 55% fat). After each diet period, VO2max and endurance (time to exhaustion at 75% VO2max) were measured. Neither VO2max nor endurance time were significantly modified by the different diets. Although time to exhaustion was greater during high fat than low fat the difference was not statistically significant.

Vogt et al (2003) also saw no decrements in performance after a HFD. 11 athletes did 5weeks of HFD (53%) or low fat diet (17%) and were tested at both moderate and high intensities. Half marathon running time differed only 12sek between diets. Vogt also showed that glycogen stores were maintained on the HFD.

In contrast to Vogt, Lambert and colleagues (1994) who used a 2 week 67% fat or 12% fat diet, showed reduced glycogen stores in 5 trained cyclists. But unlike Vogt they observed an improved performance measured as time to exhaustion at 60% VO2max. The study shows that a diet with more than 60% fat may make it hard to maintain full glycogen stores, but also that these stores do not necessarily play an important role at these intensities. The same study observed no differences between the diets when tested at 85% VO2max. The actual time to exhaustion on the 60% VO2max test was 79.7min in the HFD and 42.5min in the low fat group.

In 2003, Fleming and coworkers, assigned twenty non-highly trained men to either a HFD (61% fat) or control (25% fat). The men were tested before and after 6 weeks. The HFD group lost on average 2.2kg, but also showed small decrements in peak power output and endurance performance. The HFD group also reported increased ratings of perceived exertion. Interestingly, the average reported energy consumption in the two groups was 2335kcal and 1815kcal in the HFD and low fat groups respectively.

Rowlands and Hopkins (2002) compared the effects of 2 weeks HFD (66% fat), high-carbohydrate (16% fat) and a 11.5-day high-fat diet followed by 2.5-day carbohydrate-loading, on metabolism and short- and ultra-endurance. Participants were tested for 5 hours and all groups ingested carbohydrates during testing. The diets had no statistically significant effect on 15-minute performance, although the high-fat condition tended to reduce distance covered by -2.4% (not significant) relative to the fat with carbo-loading condition. In a 100-km time trial, the HFD and the HFD with carbohydrate loading attenuated the decline in power output observed in the high-carbohydrate condition. The corresponding improvement in performance time of 3% to 4% was not statistically significant. The authors concluded that “…there was some evidence for enhanced ultra-endurance cycling performance relative to high-carbohydrate.

It is important to remember that although some averages are not statistically significant, an improvement of for example 4% during the last 42km of a triathlon would equate to a 6min 36sek improvement in a goal time of 2h 40 min.

Although many studies show only small or no performance improvements, not many studies show an obvious decrease in performance.

In 1989 Kathleen O’Keefe and colleagues had seven highly trained female cyclists follow a low carbohydrate diet (13% carbs), a medium carbohydrate diet (54% carbs) or a high carbohydrate diet (72% carbs). The diets were isocaloric and followed for one week. After each week the subjects exercised at 80% VO2max to fatigue. Average time to fatigue was 60min for low carb, 98min for medium carb and 113min for high carb. Thus a low carb diet in this case caused a marked decrease in exercise performance. However, mark the 1 week intervention.

In 1999 Julia H. Goedecke and colleagues tested a 15 day HFD period in 16 endurance trained cyclists. They were randomly assigned to control diet (30% fat) or HFD (69% fat). The cyclists were tested on a 2.5hour constant load ride at 63% VO2max followed by a 40km time-trial. 90min before each trial subjects consumed 400ml 4.3% MCT solution. At the start of the trial the same solution was ingested containing 10% glucose. Thereafter 200ml of the glucose+MCT was consumed every 20 min until 40 min into the time-trial. 40km time trial went from 69.9 min to 65.6min in the control diet (-3.3min) and from 69.3 to 63.4min in the HFD group (-5.9min) indicating an advantage of HFD.

Several studies have examined the effects of HFD periods followed by carbohydrate loading on performance. One of these studies was performed by Burke and coworkers. The strategy was 5days HFD followed by 1 day high carb. Average time trial time was 8% faster with this strategy compared to constant high carb. More interesting is the observation that the increased performance was mostly due to two participants who improved greatly following the HFD. The same subjects showed symptoms of severe fatigue and hypoglycemia toward the end of testing on high carb diet.

This observation might indicate that HFD can be especially effective in individuals who may experience hypoglycemia during prolonged activity where carbohydrates are not ingested during exercise.

Neither high fat diets, nor high carbohydrate diets, have shown consistent improvements in scientific studies. All in all the results indicate that HFD have a greater positive effect in trained athletes than in untrained.

This was also the finding in a meta-analysis by Erlenbusch and colleagues who concluded that; “…endurance performance is enhanced following a high-carbohydrate diet, compared to a high-fat diet, in untrained individuals, while the performance response in trained individuals appears to be blunted.

But there are major weaknesses with many of the studies if we want to know whether HFD actually work. First of all is the time to adaptation. Often studies are done with less than 4 weeks intervention which is not much time for the body to fully adapt. There are also many other nutritional factors which are little controlled for, e.g. protein intake, vitamin and mineral status and fatty acid composition, carbohydrate type, etc.

There is little clear evidence of a performance enhancing effect of high fat diets. However, there are too few longitudinal studies to conclude sufficiently and the studies we do have differ in their results. Although the big picture looks inconclusive there exist definite findings of performance enhancement. In addition there is some circumstantial evidence from studies – individual performances, and there are the stories from athletes using the approach.

The studies we have to base our conclusions on are generally not designed to optimize all conditions and are often of too short duration.

There are many nutritional factors beyond macronutrient composition that affects fat oxidation during exercise. The existence of these influencing nutritional factors make it difficult to interpret results, but make it likely that conditions can be optimized and, if so, yield better results than the observed averages in many of the studies. It is natural that any performance enhancing effects of high fat diets are most likely to be seen in long duration sports such as marathon or triathlon. The “train low-race high” strategy, where carbohydrates are used at specific times to enhance performance, is likely a good strategy and also make physiological sense.