How much Carbohydrate should I ingest during a long distance hike (18 hours plus)?

Question

I'm planning on doing a long distance hike (mountain climb) for charity in the next few weeks (the wales 3000s/15peaks).

I've spent a bit of time looking into nutrition but I couldn't find a lot on how much I energy I should be ingesting for this. The nearest I could find was a cycling article on the usage of energy gels . this stated:

Guidelines suggest that for those cycling at a moderate intensity over 90 minutes, you will need between 30g and 65g of carbohydrates per hour to replace what’s being lost and maintain performance. Consuming anything more won’t improve performance. In fact, it may cause gastric distress, as the body struggles to be able to absorb such large quantities....For the everyday cyclist, 60g of carbohydrate per hour will suffice.

There are obviously a couple of flaws comparing cycling for 90 mins to walking for over 18 hours.

Can anyone give any idea how much energy/carbohydrates I should be aiming to ingest per hour throughout the day to maintain an optimal amount of energy? Preferably in g of carbohydrate as this seems to be the easiest to plan.

Obviously I'm going to be tired and there is no way I can ingest the amount of energy I will be using (we've estimated this at 8000-9000 calories) but a target would be helpful.

Answer 1

Reaching for my Kindle copy of House and Johnston's book*, I find the statement: "In an ideal world we’d eat seventy grams of carbohydrate per hour to replace the roughly 400–800 calories per hour we’re burning while climbing."

Obviously at 4 calories/gram, 70g of carbs will not supply 400-800 calories. The reasoning for this amount becomes more clear after further reading: "For athletes engaged in high-intensity exercise for thirty to sixty minutes or longer, sport science recommends consuming thirty to seventy grams (120–280 calories) of carbohydrate per hour. This is based on numerous studies that suggest endurance athletes perform best ingesting 1.0–1.2 grams of carbohydrate per minute, which is the maximal oxidation rate of carbohydrate."

Regarding long days, the authors write, "On a long all-day or multi-day effort you have to stick to conversational pace most of the time. In this case, plan to eat frequent small amounts of food balanced with carbohydrate/protein/fat such as a sandwich or wrap. Trail mix is also a nice balanced source of macronutrients. Gels and bars can work as well. Drink a bit every time you feed."

Your estimate of the total calories suggests a burn rate of 300-500 calories per hour, which is consistent with the low end of the range in that first quote, and makes sense for a less intense but longer duration effort. Keep in mind that a decent chunk of that number (at least half, if you're in good shape) will be supplied from fat rather than carbohydrate, and that the sort of endurance exercise you're doing will also increase the amount of protein that's being metabolized. Also, don't forget about electrolytes!

I take this info to suggest that 60 or 70g of carbs can be considered an upper limit, and that the number can easily be dialed down since you need to keep to a reasonable pace. If there are portions of your trek where you do need to go all-out in terms of intensity, those would be the places to be downing 3-4 gels per hour. (I'm thinking here of the smaller 90-cal, ~20g carb packets.)

You may also find some useful discussion and calculations here: http://strongswiftdurable.com/mountain-athlete-articles/ski-mountaineering-nutrition-for-alaska-trip/ (This article describes a more intense endeavor, and has an emphasis on liquid calories which you may also find useful.)

• Training for the New Alpinism

Answer 2

This page on endurance running discusses a formula of 0.7 -1.0 gram/kg body weight per hour. Although higher than your figures, the ultra endurance runner can tolerate food digestion better than a 90 minute sprint cyclist, and must also replace energy being used (A 90 minute cyclist gets the half of his energy needs from from Glycogen reserves).

You are probably considering this too late. You cannot just grab a bunch of random laboratory produced super-dupa-carbo-gel-gue bars and expect not to puke it up at the first hill climb. Everyone is different and tolerance to different foods various enormously, as does the ability to consume while exercising. The only way to get this right is through trial and error, and 18 hours walking is a long time to spend with a heavy stomach rejecting the food you have with you. If you cannot do a few trial runs, stick with foods you know you tolerate well.

Ideally for an 18 hour event, you consume protein and fats as well as carb. Your body will have consumed glycogen stores within 60-120 minutes, and you need to replace these with a steady stream of energy rather than a short bust provided by simple carbs (sugars). Complex Carb require less oxygen to digest than protein and fats, which is why they are preferred by athletes who are operating close to anaerobic thresholds, but digest moderately quickly. If you are not operating close to this threshold additional Protein and fat provides a more consistent energy release over a longer time. If only using carb for energy, you must be more vigilant about consuming small amounts regularly.

Manufactured high protein bars are ideal for this, however 'natural' foods (my preference) involving nuts, dried fruit and chocolate for snacks, along with "real" meals with some volume such as crackers and cheese, sandwiches, filled rolls works for me. Fresh fruits like an apple or banana have a place.

I find long days on laboratory produced food rodents won't eat leaves me hanging out for real food and depressed, while mates of mine can go all day on a couple of Power bars. I have had plenty of experience and well used to eating on the trot, and would rather slow down for 1/2 hour while my lunch settles than skip it - this works for me but may not work for you