Early mornings can mean long days in the hills. Prevent the bonk: consume those carbs while on the go. Photo: Patrick Fink
Backcountry touring and ski mountaineering can be all-day affairs. Proper carbohydrate intake can keep you on the go. But first, you may have to gut train with high-carb nutrition to keep the stomach settled and the motor primed.
Not again. I just reached 13,500’, and my stomach decided that now was the perfect time to pull the fire alarm and demand a full evacuation. Wag bag at the ready; luckily, this is only a minor inconvenience on a stellar day of skiing the Holy Cross Couloir. This evacuation scenario has been a recurring theme for my spring season after a winter of powder and smiles. Curious, I dove into the available research and consulted some experts to find a solution.
First, let’s look at optimal conditions. The intake of carbohydrates during endurance exercise has repeatedly been shownto have a positive effect on performance compared to fasted efforts. Durations as low as an hour have shown these same benefits to carb intake. That too-short skimo race, which seems too short to be affected by eating a gel, is indeed affected if the gel remains in the wrapper.
How much should I eat? That is the start of the “it depends” conversation, as our bodies are capable of different things and trained to various extents. Studies have shown that glucose, as a single carbohydrate source, can be absorbed by the gut at a rate of approximately 60 grams per hour (g/h). Further trials have combined glucose with an additional 30g of fructose to show that 90g/h of absorption can be achieved. Ultra runners and Grand Tour cyclists have been pushing the envelope even further through gut training gut to be able to absorb even more.
What does gut training look like? Gut training is a fairly new area of research. Positive effects have been found in studies lasting 28 days to 10 weeks. It is recommended to implement this strategy in at least one workout per week, either in a long training session or a session that most closely mimics the effort for which you are training.
Why go through all of this trouble? As someone who grew up playing soccer, where water bottles were full of water and halftime nutrition consisted of orange slices, this all seemed unnecessary. That is until I, and many of you, encountered the dreaded bonk. Common advice for treating a bonk is to slow down, drink, and eat some calories. But that’s like making billions (trillions?) of dollars manufacturing drugs to treat diseases while medical providers aren’t compensated for counseling patients with advice to help prevent the diseases in the first place. I digress.
If a fun day out that ends in a bonk can be prolonged by nutrition, what else am I missing?
I ran and biked in the off-season to train while consuming up to 75g/h of 2:1 a glucose-to-fructose mix, with solid results. I was able to go farther and faster than ever before thanks to science and a couple bags of sugar. This carried over into winter skiing, where my typical tours seemed pedestrian, and I started putting in longer days, more laps—with more smiles—all while never feeling close to bonking. Halcyon days. But then spring happened.
Objective skiing lured me out into new terrain, and new stomach issues. Here’s what changed. There were earlier wake-ups, longer days on average, prettier views, and the big one, higher altitude. It turns out our bodies experience something called hypoxia-induced insulin resistance when subjected to acute altitude exposure (hours vs. weeks). This condition may affect different individuals at different elevations. I live at around 6,000’ (1,800m) and have experienced no issues in my normal winter touring zones, which are 8,000-10,000’ (2,400-3,000m). As soon as I’m crossing into 13,000’ (4,000m) and above, that is no longer the case. The reason for this is not fully understood. But, the result is a backup in the carbohydrate pathway from food to the muscles.
When comparing the change in fuel usage at low elevation versus high elevation, there is a shift away from consumed carbohydrates (exogenous) and toward carbs already stored in the muscles and liver (endogenous). This makes me think that not all of those performance-enhancing carbohydrate benefits are nullified; rather, they are rescheduled. Instead of placing a heavy emphasis on intake during high-elevation efforts, more emphasis can be placed on loading the storage in the liver and muscles beforehand.
Carbohydrate Loading
The objective of carb loading is to increase carbohydrates stored in the muscles and liver. This involves an increase in total carbs consumed, combined with a decrease in activity level (often called a taper).
Carbohydrates are the macronutrient we are increasing. It is not just general overeating of fats and protein. Try to limit fiber to what your body is accustomed to (a minimum of 25 grams for general health). Aim for around 100-150 grams per meal for the 4-5 meals prior to the effort. A decrease in activity helps to shuttle those carbohydrates into storage instead of being used for fueling more activity.
Other Helpful Tactics
Interestingly, with summer around the corner, it is good to know that our bodies exhibit a similar response to high heat: utilizing more carbs while also limiting the use of those ingested mid-exercise. Both responses can be decreased with heat acclimatization. A week or two of sauna exposure can help boost plasma volume and all of the benefits that come with it. Twenty-five minutes each day for five days is a great starting point.
A couple of supplements have been shown to help maintain gut resilience during long efforts:
- Probiotics—In general, the more CFUs and strains that are included, the better.
- Glutamine—Up to 0.25g/kg one time, 2 hours before the effort.
References:
Thank you to Dr. Kyle Pfaffenbach and Dr. Asker Jeukendrup for your insights.
Jeukendrup, Asker. 2014). Step Towards Personalized Sports Nutrition: Carbohydrate Intake During Exercise. portsmedicine (Auckland, N.Z.). 4 Suppl 1. 25-33. 10.1007/s40279-014-0148-z.
Pasiakos, Stefan M.; Karl, J. Philip; Margolis, Lee M.. Challenging traditional carbohydrate intake recommendations for optimizing performance at high altitude. Current Opinion in Clinical Nutrition and Metabolic Care 24(6):p 483-489, November 2021. | DOI: 10.1097/MCO.0000000000000782
Burke, L. M., Hawley, J. A., Wong, S. H. S., & Jeukendrup, A. E. (2011). Carbohydrates for training and competition. Journal of Sports Sciences, 29(sup1), S17–S27. https://doi.org/10.1080/02640414.2011.585473
Kerksick, C.M., Arent, S., Schoenfeld, B.J. et al. International society of sports nutrition position stand: nutrient timing. Journal of the International Society of Sports Nutrition14, 33 (2017). https://doi.org/10.1186/s12970-017-0189-4
A great summary, and definitely some additional nuggets I will be looking to incorporate. For those who have trouble eating enough while in aerobic output, drinking your carbs can really help. I buy bulk maltodextrin and fructose on the internet, and use a scale to hit the desired glucose-to-fructose ratio. Much cheaper than the high carb mixes the supplement companies sell!
Will, That’s great to hear you are going the DIY method, cheaper and easier to dial in the glucose:fructose ratio you find works best. I do the same for days ~3 hours or less and then think about adding electrolytes when the demands get higher.