By David Jeker - Endurance coach and sports scientist specialized in ultra-endurance
The subject of ultra-endurance nutrition is tricky and opinions are very divided. However, the scientific literature on this topic is quite abundant and the recommendations are clear. Before embarking on this delicate subject, I would like to point out that I am not a nutritionist, but a researcher in sports sciences. The elements presented in the following lines are based on my interpretation of the scientific literature as well as my experiences as a coach and as an athlete. I will stick to the strategies to be used during the race and let nutritionists tell you what to eat before and after exercise.
Carbs. Regardless of your beliefs regarding diets or methods to enhance fat-adaptation, the goal is always the same: spare your glycogen reserve. Glycogen is the form in which carbohydrates are stored in the body and this reserve is limited to about 500 grams (2000 kcal). However, even a skinny athlete has a lot of energy stored as fat and it is more difficult to digest lipids than carbohydrates it does not make sense to consume lipids during exercise. This hold true even if you follow a ketogenic diet. Optimizing the use of the carbs we eat and our stored fat to propel ourselves is the way to go.
For competitions lasting more than 2 hours and a half, it is recommended to consume 90 grams of carbs per hour. For example, one XACT fruit bar contains 25 grams of carbs so 3 to 4 per hour to optimize performance. It is very important to start fueling early in the race to spare glycogen stores. I usually eat my first portion 15 minutes into a race and maintain this rate until the end. It may seems like a lot, but even 120 grams per hour (500 kcal) would be way under the energy expenditure. A recent study showed that 120 grams per hour is actually more beneficial than 90 for highly trained runners during a mountain marathon (2000 m D+) . At these higher intake, the glucose-fructose ratio is important to maximize the absorption. A ratio closer to 1:1 is considered ideal. A lot of carbohydrate-rich food contains mainly sucrose, a sugar molecule combining one glucose and one fructose so the ratio is often naturally near 1:1. Sport nutrition products containing mainly maltodextrin, a complex carbohydrate composed solely of glucose, can be harder to absorb at higher dosage. Furthermore, it is important to understand that while exercising, the body won’t produce much insulin. It prevents the sugar consumed to be stored when it is needed in the active muscles. The rationale supporting an avoidance of simple sugar in everyday life does not apply to its consumption during exercise.
Intestinal absorption isn’t necessarily related to the level or weight of the athlete. A lighter runner, requiring less energy to move at a certain pace may be able to compensate a greater proportion of its energy expenditure. The same goes for slower athletes. Even at low speed, it is almost impossible to replace all the energy burned. We spend around 1 kcal per kilometer-effort per kilogram of body mass. For example, a 60 kg runner will spend about 2280 kcal to complete the 28 km of the Ultra Trail Harricana (1000 m D+). For a 3h30 finishing time, it still makes 650 kcal per hour.
It is important to know that consuming carbs during exercise is the best way to maintain the blood flow to the digestive tract which allows to avoid digestive problems. It is not just about performance, a minimum intake of 60 grams per hour would be required to maintain proper digestion. The feeling of not wanting to eat anything sweet is likely related to a slowed down digestion and stopping to fuel in this situation is the worst solution. Practicing your fueling strategy during longer training runs can help improve the absorption. In fact, an high intake of carbs daily, which should be the case if you exercise a lot, also helps to improve intestinal absorption.
The science isn’t as clear about that. Studies showing an advantage to the consumption of proteins during exercise often add them on top of carbs. In this scenario, the beneficial effect would be mostly related to the increase in caloric intake. Studies replacing part of the carbs by amino acids are not as positive. However, if the consumption of protein does not affect negatively the absorption, it is totally okay to have some. I struggled in a couple races with a sport drink containing proteins so it is not part of my nutrition plan for ultras anymore and I stick to carbs. For an ultra of extreme duration, lasting more than one day, it makes a lot more sense to consume proteins. However, it is also likely that you eat some real foods during such an adventure and therefore consume some proteins.
Considering that it is advantageous, for most humans, to drink based on the sensation of thirst, I prefer to drink only water. This way, my hydration and nutritional strategies are totally independents. Of course, it is possible to have liquid carbs, but it is important to estimate the correct concentration to avoid having to drink more fluid than dictated by your thirst to have enough carbs. To consume a portion at a regular interval, I program an alert on my watch. For example, I eat one XACT fruit bar every 15 minutes. It adds up to 100 grams of carbs per hour. I can always adjust the rate based on my feelings. Reducing the intake if digestion feels more difficult or increasing it if I have negative thoughts or lack motivation. For me, the interval between portions will normally remain between 12 to 20 minutes (75 to 125 grams per hour). Contrarily to the perception of thirst, hunger may not be very accurate during exercise… We often bonk before we feel hungry! Also, the lack of motivation to eat your next portion is a good sign that you absolutely need it and avoid ending up with a slowed down digestion.
For me, aid stations are useful to replace a portion by some real food. The options are rarely easy to transport so I prefer to have my own nutrition in-between aid stations. Even if you are desperate for salted food, it is advised to avoid the salted peanuts or chips (unless they are oven baked, hence contain less fat). The absorption and usage of lipids, especially longer chain lipids, isn’t very effective. However, salt hunger should not be ignored, but carbohydrate-rich salty options are more interesting. Adding electrolytes to your water if you feel a need for salt is also possible. My favorites aid stations food are salted potatoes or rice balls.
For the 125 km of the Ultra Trail Harricana that I should complete in about 14 hours, I’ll need 55 portions of 25 grams of carbs. There are 10 aid stations on the course, 9 with food. Therefore I need 44 XACT fruit bars, 22 in my race vest at the start and 22 in my drop bag accessible at the mid-point of the race. That is what I do, but also what I recommend. Not necessarily product from XACT nutrition, but these are easily transportable, taste great and aren’t expensive compared to other sport nutrition options. I may also add some ketone esters to my nutrition plan, but this subject deserve its own post.
No and I do not have a sweet tooth at all. Like most runners, I did make the common mistake of waiting for the next aid station, the one that never comes, to eat something else than what I have on me… An great way to sabotage your race and miss and opportunity to experience a perfect ultra.
The most important thing to understand is that a minimum of carbs (60 g/h) is required to avoid problems during an ultra. If you want to perform better, finish with a smile on your face, recover faster or simply enjoy your race more, it is better to have more than this minimum. Drink to thirst and avoid non-steroidal anti-inflammatory drugs at all cost are also great ways to avoid putting yourself in danger. Have a nice race!