MdS Nutrition Research

Time flies, and the Kalahari Augrabies Extreme Marathon (KAEM) is getting closer. This means that there are many who are starting to take a closer look at nutrition and in specific what to take with and how much. I hope this entry will answer some questions for you.

The data was extracted from the Marathon des Sables (MdS) 2013 research I conducted.

Energy

There are a number of models that can be used in determining an individual’s energy requirements. Among the various approaches there is the Harris-Benedict equation, the revised Harris-Benedict equation, the Mifflin St Jeor equation, Katch-McArdle formula and the Cunningham formula, to name only a few. Various factors are taken into consideration such as gender, heart-rate, body weight, activity etc. However, their end result is the same, to determine an accurate figure that represents the energy requirement for a person given a certain level of activity. What is more significant is that all of these formulas deliver different results for, essentially, the same set of bio-data. New research continues to refine the calculations and with each step we are getting closer in determining a more accurate answer.

But calculating energy is only one factor in the energy requirement ‘basket’, other factors such as energy conversion efficiency (which may differ from one person to the next), and an individual’s ability to extract usable energy efficiently from fat reserves are once again only some of the factors to consider. Biological functions such as organ functions (including the brain), respiration and digestion all consume part of the energy that is ingested. Stephen Seiler, in his 2005 book entitled – Efficiency, Economy and Endurance Performance – notes that the efficiency of converting available energy (from food) into mechanical energy (muscle action) in humans are somewhere between 18% and 26%. Then the energy absorption rate for different foods is also an additional compounding factor that could have a huge impact on an individual who participates in an endurance activity.

With an energy conversion efficiency of between 18% and 26% the energy requirement variance is significant. If we assume 100% absorption for two individuals of the same weight, gender, height, fitness level etc. with the one functioning at 18% energy conversion efficiency and the other at 26% efficiency the energy requirement would look vastly different.

Most of the formulas and calculations make use of various factors that, to some extent, accommodate for the energy conversion efficiency variance between individuals, but even with these factors a median approach is followed. This means that given the best calculation approach there will always be individuals who fall above and below the ‘average’. I, therefore, turned to measuring the actual energy consumed by the various MdS runners and related this to individual performance. I did assume that the energy absorption for the diversity of foods consumed during the event by the various individuals would be similar across the data sample.

What I found was that the calculations has a significant margin of ‘error’ in that it over inflates the requirement for an event like the MdS or KAEM. As these events are isolated and differs significantly from ‘normal’ everyday life the results of the sample data should not be applied to everyday life but should be limited to an endurance event. Factors such as carbo-loading prior to the event and general lifestyle prior to the event plays a role and should not be discarded.

Energy Requirement

The most comprehensive calculation approach results in a broad view that an individual would require around 44.11kCal’s per kilogram of body weight per day, of if related to a 250km race distance around 1.18kCal’s per kilogram of bodyweight per kilometre. These calculations balance the high metabolic activity with a resting metabolic rate to derive at a result. I was interested to see how this compares to the runners in a real race environment.            

At first I only looked at the average for all men and women independently. From the initial data view woman who had completed the MdS consumed only 37.1kCal’s per kilogram of bodyweight or related to distance consumed 0.83kCal’s per kilogram of bodyweight per race kilometre. Men on the other hand consumed slightly more at 37.9kCal’s and 0.85kCal’s respectively.

I then proceeded to view the data in-terms of performance. Keeping to the top 10%, next 20%, next 40%, next 20% and last 10% methodology which I started-off with at the beginning of this series.

Position	kCal’s per kilogram of body weight per day	kCal’s per kilogram of body weight per race kilometer	kCal’s per kilogram of body weight per day	kCal’s per kilogram of body weight per race kilometer
	Female		Male
Top 10% 1 to 100	34.7	0.78	40.7	0.91
Next 20% 101 to 300	40.7	0.91	37.9	0.85
Next 40% 301 to 700	29.4	0.66	38.6	0.86
Next 20% 701 to 900	40.8	0.92	36.0	0.81
Last 10% 901 to 1000	39.8	0.89	36.0	0.81

Amongst the male runners it seems to indicate that the top runners consumed more energy than the rest of the field. This, however, does not hold true for the female runners. What is important to note here, is that the relationship between adequate energy input and race performance continues to be supported. Men and women seems to respond slightly different, men seems to respond positively to an increase in calorie consumption whereas women seems to reach a performance levelling in relation to an increase in calorie consumption much quicker. Yet again the figure seems to be more fluid than expected, or indeed what I have hoped for.

Energy Consumption Variance within the Data Population

I then considered the minimum and maximum variance amongst each of the performance groups. What this means is that I identified within a particular performance group the minimum and maximum variance given, from this I determined the average variance within the particular group. The aim of this is to find the energy consumption across the entire performance group. With this in-hand sufficient provision is made to accommodate individual tolerance. This was done across the gender spectrum. With this variance in-hand it is possible to extrapolate the particular energy requirements for each performance group, taking into consideration the absolute minimum energy consumed as well as the absolute maximum. 

For both male and female runners performance seems to decline once the optimal boundary is exceeded. On the one-hand to little calories means that a runner might be running on “empty” for large parts of the day. This would obviously impair performance. On the other hand to much calories contributes nothing additional to the runners performance and represents ‘dead’ weight as far as running weight goes. Please note I definitely do not advocate cutting race weight by taking too little nutrition, as a matter of fact I, personally, carry between 5 and 10% additional calories to ensure that I have sufficient reserves to accommodate for any margin of error. In previous years some runners have lost the trail and ended up running an additional 10 or 20km on a particular day. For a 70kg male a 20km mistake, based upon an optimal calorie count, would result in an additional 1,274kCal (or 5,223kJ). If no reserve was included in the initial calculation this would represent a substantial shortfall.

Psychological Effect

We must not discount the psychological effect of nutrition. Perception pays as much a role as anything else. MdS finishers were asked, after completing the race, whether they felt they had enough calories during the race.

Amongst the top 10% of runners those that fell below the 0.87kCals (male) and 0.63kCals (female) mark, all indicated that they felt that they did not have enough calories. Amongst most other finishers those that responded that they did not have sufficient calories seem to have less tolerance for deficiency, here male runners indicate insufficient calories at around the 40kCals mark (0.90kCals) while women mostly touched on the 28.1kCal mark (0.63kCals). From this it seems as if women typically have a greater perception tolerance, whereas men seem to respond negatively to nutritional shortfall even when the shortfall is not realised yet.

Type of Food

Over the past two years I have repeatedly seen exchanges between runners pertaining to the use of re-hydrated food versus off the shelve food. During the MdS research runners were asked to class their food stuffs. Amongst the group 48% indicated that they make use of a mixture of re-hydrated and supermarket food, 46% indicated that they only made use of re-hydrated food while the remaining 6% indicated that they only took with supermarket food.

Post race a second question assessed the runners own experience with the food they had taken. 73% indicated that they had mostly the right type of food, 4% indicated that they had taken mostly the wrong type of food while 23% indicated that the food they had taken was totally the right type of food. What was interesting is that the only group where 100% of the respondents indicated that they had taken the right type of food was the group that only purchased supermarket food. My personal view on this is that it may be a case of familiarity. The dissatisfaction with re-hydrated food may simply be that many runners don’t adequately test their food pre-race. This has nothing to do with the actual food but rather, relates to personal preference and how an individual’s body responds to nutrition.

The survey neglected to ask whether food was tested prior to the event and to what extent it had been tested. Hopefully this can be assessed during the 2014 MdS which may provide more clarity on the issue.    

Food Group Composition

Fat, Protein and Carbohydrate composition seems fairly normal across the entire respondent sample with Carbohydrates coming in at 67%, Protein at 25% and Fat at 8%. There were some notable exceptions among these, the following might be noteworthy.

Race Position	Protein (%)	Fat (%)	Carbohydrate (%)
Top 10 Position	20	25	55
Top 300 Position	25	20	55

I am aware that it is problematic to deduce or infer anything from such an insignificant sample, so no claim is made as to the link between performance and food composition. What is interesting, however, is that both runners had a significantly reduced carbohydrate diet (12% less than the usually recommended norm, yet both completed the race and one, at least did so with a high level of performance). This warrants additional research and I hope to identify a larger group of predominantly fat / protein based runners whose performance can be tracked.

Sports Drink
     

Not all runners take sports drinks during a race or event. During the MdS 65% of finishers did make use of sports drinks during the event while 35% drank only water. There is no clear indication that links sports drinks during the event to performance.

Amongst the runners who did make use of sports drinks 57% drank it throughout the day, 34% only drank it at the end of the day, 7% at the start of the day and 2% when they felt they needed it. Even among this group there is no noticeable advantage that links drinking methodology to performance.  

Carbo-Loading

57% of MdS runners did carbo-load prior to the event while 43% indicated that they did not. The type of carbo-loading was not determined. Those that make use of carbo-loading are spread throughout the field as is the group that don’t. Even among the top runners there is no conclusive trend that links carbo-loading to performance. Unfortunately, what is understood by the term carbo-loading might also play a significant role in the responses. As many of the runners live on a predominantly carbohydrate based diet, they are in actual fact carbo-loading although they don’t interpret it as such or actively set-out to do so. I do suspect that once the concept of carbo-loading is better defined we might find that a much larger percentage actually engage in the stocking-up on carbohydrates.

Sodium, Potassium and Hydration

During events like the MdS or KAEM most runners and all medical personnel is acutely aware of dehydration and sodium depletion. This is actively managed and to a large extent supplemented through the sodium content of race food. Often the sodium intake through food, sports drinks and snacks provide more than sufficient sodium so addition sodium intake through tablets may not be needed.

Water will always be in short supply and some level of dehydration is expected, this is why these events is classed as extreme. It is, however, not the lack of water that causes many runners to become dehydrated but rather their water intake regime. Many of the runners who became dehydrated did not drink constantly during the day but drank large amounts of water at the check-points.

Potassium on the other hand is not that easily recognised and managed. Many of the symptoms associated with potassium depletion and/or even reduced potassium levels are similar to sodium depletion and dehydration. The notable exception is that once a race is over runners return to a normal eating regime whereby hydration is paramount and sodium levels are increased through normal food intake. Sodium levels stabilise and return to normal, as do fluid levels, this typically happens within a day or two. I therefore asked runners during the post-race assessment to indicate whether they continued to experience, up to two weeks after the event, a number of symptoms, all of which are the typical symptoms that is associated with reduced sodium levels and dehydration.       

A total of 4.4% of finishers continued to experience typical dehydration and reduced sodium level symptoms up to two weeks after the MdS. However, there are a number of very significant symptoms that need mentioning: 14% indicated a general feeling of depression, 10% a general lack of energy, 12% leg severe involuntary muscle cramping during the night, and 27% reported sleepiness and tiredness.   

Without additional testing such as blood-tests, urine analysis and ECG to name a few possible measurement methodologies, it would be impossible to definitively state that extreme runners experience a significant potassium level decline, however, the post symptoms provides a strong indication that this may be so. Additional research would be required to confirm my preliminary observation. In the meantime extreme and ultra-endurance runners would benefit from supplementing their pre-race, race and post-race diet with potassium rich foods.   

Conclusion

There are a number of elements that remains unanswered and requires some additional research before a definitive answer can be given, however, from the available data the energy requirement spectrum for both males and females seems well defined. What every individual must determine beyond the basic physical element of the energy requirement spectrum is at what point does the feeling of hunger, or the perception of having inadequate food intake, impacts negatively upon him or her as an individual. This is not as easily quantifiable and is a very personal element in the equation.

Thank you for reading my blog and see you soon.

Genis