March 18, 2011 by Bill Henderson, MD · 19 Comments
[While iRunFar rarely touches on the technical aspects of running fitness, we received an offer we couldn't refuse from our good friend and exercise physiologist Dr. William Henderson of Endurance Science. In the following article, he explains an approach to race nutrition using his 2009 Marathon des Sables as an example.]
In this article, I outline some of the information I used to prepare nutritionally for the 2009 Marathon des Sables (MdS). The strategies are applicable in large degree to other races and types of events. As always, try nothing new on race day(s).
There is a great deal written about pre-race carbohydrate loading strategies. I think that the evidence supporting these is reasonable, but the reality of complex loading strategies is complicated by athlete motivation and the demands of travel and timing specifically related to the MdS. Traditional carbohydrate loading strategies usually involve one or more runs associated with carbohydrate restriction for several days (i.e., 2-4 days) prior to the big event. The purpose of these days is to thoroughly deplete liver and muscle glycogen stores. This depletion stimulates the activity of glycogen synthetase – the enzyme largely responsible for causing glycogen production and storage – beyond it’s normal levels activity. The athlete then eats large doses of carbohydrate, in an effort to saturate the body’s glycogen storage. It is theoretically possible to store enough glycogen this way to last a full marathon distance.
I think that this specific type of protocol is not needed for MdS nor for many other ultra-distance races. There are three reasons I would not recommend aggressive depletion-loading techniques
Firstly, here are several risks. Specifically, running several long runs prior to the start day means running whilst tired from travel, which increases the risk of injury and illness. I would worry that this places too much physiologic strain on an athlete. It is my impression that fewer and fewer top athletes and coaches are using these strategies anymore because of the psychological and physical effects.
Secondly, the benefits of aggressive loading strategies diminish when the athlete is able to maintain blood glucose levels during running by eating. It is far more important to maintain adequate carbohydrate intake whilst running than to focus on difficult pre-race loading strategies. Given the multi-day nature of MdS, the small positive benefit in terms of liver and muscle glycogen density on day 1 is minimal.
Thirdly, you will naturally undergo carbohydrate loading and glycogen storage during the week prior to the MdS or other races as you taper your mileage. It is not necessary to eat massive amounts of carbs in the days prior to the race start. If you eat your normal amount of calories (possibly focused slightly more on carbs than usual) whilst dropping your training mileage, you will naturally store glycogen and fat.
Besides carbohydrates, it is useful to think about “topping off” your electrolyte and water stores, too. Travel to the competition, dry environments, and stress will all alter your water and sodium balance. Careful attention to hydration and a modest increase in sodium intake for 3 days prior to the race start will be of benefit.
In the case of MdS, all of these strategies will cause you to be 0.5-2 kg heavier at the start line than your usual race weight. That’s not a bad thing – think of the weight as fuel.
Overnight, your liver glycogen stores can deplete by as much as 50g (of 100g total). Your muscle glycogen stores (400g) are unaffected. One of the main purposes of the pre-race meal is to top off your liver glycogen stores. As it takes a while to fully digest your breakfast and form glycogen, this meal should happen about 2-3 hours pre-race start. Again, a relatively high carbohydrate percentage is called for (80% or more).
There are some additional theoretical reasons why eating your pre-race meal within 2-3 hours may impair performance, particularly if your meal is composed mostly of simple rather than complex carbohydrates. It is possible that after the meal you will secrete a lot of insulin. This may lead to the inhibition of lipid mobilization (fat burning) during aerobic exercise, which means reduced fats-to-fuels conversion, and thus potentially less available energy. Additionally, high insulin levels may enhance muscle glycogen depletion during exertion.
If you finish your pre-race meal about three hours prior to start time, your insulin and blood glucose levels will have to normalize, thereby avoiding these problems. After three hours, hormonal balance is restored, and you won’t be at risk for increased glycogen depletion. Eating within three hours of a race promotes faster release/depletion of both liver and muscle glycogen and inhibits fat utilization. The combination of accelerated glycogen depletion and disruption of your primary long-distance fuel availability may impair your performance.
Summary: Eat a meal rich in complex carbohydrates 3-4 hours prior to start time
- Costill DL, Hargreaves M. Carbohydrate nutrition and fatigue. 1992, Sports Med., pp. Feb;13(2):86-92.
- Costill, DL. Carbohydrates for exercise. Dietary demand for optimal performance. 1988, Int J Sports, pp. 9:1-18.
- Hargreaves, M. Pre-exercise nutritional strategies: effects on metabolism and performance. 2001, Can J Appl Physiol., pp. 26 Suppl:S64-70.
- Hawley JA, Dennis SC, Noakes TD. xOidation of carbohydrate ingested during prolonged endurance exercise. 1992 , Sports Med. , pp. Jul;14(1):27-42.
- Wee SL, Williams C, Tsintzas K, Boobis L.Ingestion of a high-glycemic index meal increases muscle glycogen storage at rest but augments its utilization during subsequent exercise. 2005 , J Appl Physiol., pp. Aug;99(2):707-14.
- Coyle EF, Coggan AR. Effectiveness of carbohydrate feeding in delaying fatigue during prolonged exercise. 1984, Sports Med., pp. Nov-Dec;1(6):446-58.
- Dennis SC, Noakes TD, Hawley JA. Nutritional strategies to minimize fatigue during prolonged exercise: fluid, electrolyte and energy replacement. 1997 Jun, J Sports Sci., pp. 15(3):305-13.
Carbohydrate is the best fuel for your body during intense exercise. Endurance athletes can only store about 400g of muscle carbohydrate (as glycogen) and around 100g of liver glycogen. This amounts to not much more than 2,000 kCals (500g x 4 kCal/g) in total – enough for about 15 miles of fast pace running for a 165 pound athlete.
Happily, well-trained endurance athletes can supply some of their energy needs from fat, even at moderately high intensity levels. Although fat and protein can both serve as fuel sources, carbohydrate is still essential for high intensity performance. There are several reasons why carbohydrate is an important fuel, but one of the most important is that only carbohydrate can supply energy rapidly enough to generate ATP (the energy releasing molecule used to drive muscular contraction) during vigorous exercise. Furthermore, even when exercise intensity is lower, and more of the energy can be derived from fat, a continual breakdown of carbohydrate is required to allow the efficient oxidation of fat for energy.
So how much carbohydrate should be eaten during running? The answer is essentially “as much as possible.” For example, assuming an athlete runs 6 miles/hr (very fast over this terrain – less than 5% of competitors can achieve this!) during the MdS, and given the difficulty of the terrain (30-50% more energy needed per miles run than normal trail or road) a 165 pound athlete will burn approximately 1,000 calories per hour. Most athletes of this size can only ingest around 250-300 cal/hr. So no matter how much you eat, you will still be “running a deficit.” Your goal should be to eat as much as feasible without causing nausea. This is typically around 250 calories per hour.
Many people feel that a bit of protein makes them feel better during long efforts. If this is true for you, then use a food plan that has some protein in it. I would not recommend foods with significant fat in them if your effort is going to be intense. Ingested fat slows down the emptying of food from your stomach (potentially leading to nausea), and is not readily available as an energy source during exertion. Some people deliberately include fat in their intra-race food for very long events – specifically because it improves taste/palatability and the sense of “fullness.” These seem like good reasons to me – but don’t do it simply to “get more calories,” it doesn’t work that way…
Summary: 250 kCal an hour (if you can) from the first to the last step of the race. Focus on carbohydrates!
Eating large amounts of two different carbohydrates during prolonged exercise allows greater conversion of carbohydrate to energy than ingesting one alone. Combining maltodextrin with fructose can elicit higher carbohydrate oxidation rates during exercise than maltodextrin alone because they use different intestinal carbohydrate transporters. This means that more carbohydrate can be absorbed from your intestinal tract more quickly, potentially decreasing fatigue and improving performance…Peak conversion of ingested carbohydrate to energy measured during the last 30 minutes of exercise was about 40% higher when athletes used a combination of fructose and maltodextrin (1.5g/min) versus maltodextrin alone (1.06g/min). There are a vast number of powders and gels available. You may wish to experiment with ones that contain a mix of fructose and maltodextrin as fructose can cause discomfort and diarrhea in some athletes.
At the end of each day’s effort at the Marathon des Sables, you will probably want to hang out with other runners, relax or just sit and wish you had never signed up for such a ridiculous race. There or after any other long race, you may not be thinking much about eating, particularly if you are hot or feeling nauseous. However, it is essential that you work on early restoration of your glycogen stores. A classic exercise science study showed that a typical diet (with about 45% of calories derived from carbohydrate) produced a steady depletion in muscle glycogen during three successive days of running training (10 miles per day).
However, when runners were given additional dietary carbohydrate, they achieved near maximal repletion of muscle glycogen within 24 hours. We know that the timing of this carbohydrate reloading is key. The highest muscle glycogen synthesis rates occur when large amounts of carbohydrate (1-1.85g per kg of body weight per hour) are consumed immediately after exercise and at 15- to 60-minute intervals thereafter, for up to five hours.
It seems possible that combining protein with carbohydrate in the two hours after exercise can nearly double insulin release, which results in more stored glycogen (insulin is a powerful hormone that is centrally involved in the management of glucose levels and in carbohydrate/glycogen storage). The optimal carbohydrate to protein ratio for this effect is 4:1 (four grams of carbohydrate for every one gram of protein). One study found that athletes who refueled with carbohydrate and protein had 100 percent greater muscle glycogen stores than those who only ate carbohydrate. Consider adding protein or amino acids to your post effort meal (0.4g of protein per kg of body weight).
Summary: Eat 1-2 g/kg carbohydrate within 30-60 min of exercise. Repeat this every hour. Consider adding 0.4g/kg protein to this to increase glycogen re-synthesis and muscle recovery.
- Williams MB, et al. Effects of recovery beverages on glycogen restoration and endurance exercise performance. Betts JA, et al. 2003 Feb;, J Strength Cond Res. , p. 17(1):.
- Ivy JL, Goforth HW Jr, Damon BM, McCauley TR, Parsons EC, Price TB. Early postexercise muscle glycogen recovery is enhanced with a carbohydrate-protein supplement. 2002, J Appl Physiol., pp. Oct;93(4):1337-44.
- Zawadzki KM, Yaspelkis BB 3rd, Ivy JL. Carbohydrate-protein complex increases the rate of muscle glycogen storage after exercise. 1992 , J Appl Physiol. , pp. May;72(5):1854-9.
- Levenhagen DK, Carr C, Carlson MG, Maron DJ, Borel MJ, Flakoll PJ. Post exercise protein intake enhances whole-body and leg protein accretion in human. 2002, Medicine and Science in Sports & Exercise, pp. May; 34(5): 828-37.
- Miller SL, Tipton KD, Chinkes DL, Wolf SE, Wolfe RR. Independent and combined effects of amino acids and glucose after resistance exercise. 2003, Medicine & Science in Sports & Exercise, pp. March; 35(3):449-55.
Call for Comments
What’s your fueling strategy before, during, and after a race? What strategies have you tried that didn’t work for you?