Marathon des Sables - A test of body, mind and dietitians!

Endurance sports take many forms, which is why it's so interesting to work with endurance athletes from a nutrition perspective. The general aims are more or less the same, but the practical reality of each event type creates enormous diversity in how those basic nutiritonal goals are executed. And at the extreme end of the practicality scale lies the Marathon des Sables - a multi-day, multi-stage foot race across the Sahara in Morocco. 

Image Source: Marathon des Sables Facebook page

What makes the Marathon des Sables such a challenge practically is the event's philosophy and reliance on self-sufficiency. Competitors are required to carry all their clothes, bedding, equipment and food for the entire 7 days with them. All they're provided with is a tent to sleep under, and water rations each day. Race rules stipulate that competitors must start the race with sufficient food to supply at least 2,000 calories a day for every day of the race. After each day there must still be at least 2,000 calories a day left for the remaining days of the event.

As you can imagine, running with a pack full of food and gear is no easy task. Competitors generally aim for a pack of less than 9kg in total, and 5kg or less of food. For the average competitor, every extra 100g carried requires an extra 26 kJ of energy* on the shortest days of the race and up to 52kJ on the longest stage, and so the benefits of increasing the calories and minimising weight is the great challenge for competitors and their sports dietitians.

In 2013 I worked with two clients for Marathon des Sables:

• 43 year old male, started the race at 92kg
• 41 year old make, started the race at 71kg

There were several aims from a nutrition perspective:

1. Achieve at least the minimum daily calorie requirement, for the least amount of weight possible
2. Ensure adequate carbohydrate during and after each stage to optimise running performance
3. Ensure frequent post-stage serves of protein to optimise recovery
4. Ensure the diet provides enough sustenance to prevent hunger (given the daily quantitiy will be less than normally eaten in endurance running)
5. To prevent constipation over the 6 days of the event

Without including the entire plans here, the aims above were achieved by including two main meals, two extra recovery snacks and the during-race food and fluids:

• Breakfast consisted of dehydrated meals (muesli or porridge in most cases) with added water.
• During race food was typical of what you'd normally use in endurance running events, but less emphasis on gels because they include the fluid weight (ie. they're not in powder or other dehydrated form).
• Immediately after the stage was a snack consisting of high quality protein to optimise recovery, as well as carbohydrate to refuel.
• Dinner was another dehydrated meal that provided plenty of protein, carbohydrate and veggies for fibre and micronutrients.
• An evening snack provided a third serve of protein to further optimise recovery, eaten around 3-4 hours after dinner, just before going to sleep.

Overall these two athletes consumed well over the 2,000 calorie per day minimum (one averaged 3,000 Cal per day, the other 3,150 Cal per day). They ate less carbohdyrate than I would normally aim for during a fully supported run, because carbohydrate only provides 4 calories per gram of weight. In contrast fat provides 9 calories per gram, and so is a much more weight-efficient source of energy when you have to carry it with you. But the two athletes still averaged 5.5 and 6.5 grams of carbs per kg of body weight each day.

Initial feedback from the guys after the race suggested that the extra calores and weight compared to many competitors helped them significantly, as they found themselves fatiguing less in the latter stages compared to others. They also found that a lot of clients complained about being hungry throughout the week of the race, whereas the appetites of these two were far better satisfied. One of the two runners (the 71kg one) finished the race in the top 75 overall, the larger runner ended up in the top 180. This was a better than expected result for both of them.

With several Accredited Sports Dietitians in Australia working with Marathon des Sables competitors in 2013 we're looking at pooling our data for a case study, using data from 5-10 runners to look at what worked well and what didn't. From initial conversations it sounds like all our clients carried more calories than the minimum requirement, and despite the current hype surrounding low carb, high fat diets none of these runners employed this strategy.

* Based on the calculations from Givoni & Goldman, J. Appl Physiol 30(3);429-433 (1971), assuming a 40yr old, 70kg male athlete, running with a 9kg pack, at an average speed of 6km/hr on sand dunes with no extra hill gradient factor added in.