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For my mountain climbing activities, will eating more calories will allow me to perform a bit better / longer? Is there is an upper limit on the amount of calories a person's body can absorb every day, be it through fat, carbohydrates or protein?

As an example: My standard dehydrated expedition pack has about 1300kJ / 100g. That is about 310kCal / 100g. One pack contains about 600g of food, so I end up with 1860kCal for one meal. For a multi-day expedition I would eat two of those plus some extra bars etc. Giving around 4500kCal per day. Would my body be able to absorb more, and would it be beneficial to my performance?

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If you are wondering why the other question isn't off topic: It is relevant for a lot of people when they try to plan their exercise nutrition. Your question however is rather theoretical and has no relevant effect on the topics we discuss here. It is a purely scientific question in the field of Nutrition. –  Baarn Jan 3 '13 at 12:58
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Well, I think this really depends, if it is on topic or not. As a mountain climber, I am very much interested in calorie intake. Not so much in protein intake. This is "nutrition as it relates to exercise" as specified in the FAQ, so I would disagree. However, many questions (including this one) border on many fields of interest. –  Arne Jan 3 '13 at 14:32
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@Arne - It doesn't depend. As the question is stated, it is off topic. If you want it to be on topic, then it needs to be edited to include the activity and how it is related. "How many calories can be eaten" is a theoretical, nutrition only question. The other protein question you cite I would probably classify as off topic as well, as the only "fitness" portion of it is "assume I exercise". –  JohnP Jan 3 '13 at 14:40
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Allright, I tried to make it more on-topic. –  Arne Jan 3 '13 at 14:51
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As I think this question has some value, I've taken the liberty of modifying it some more to fit within the scope of the FAQ. If you feel that the edits change the question that you are asking too much, please feel free to re-edit the question. I believe that the accepted answer still meets the questions stated. –  Nathan Wheeler Jan 11 '13 at 16:08
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1 Answer

up vote 7 down vote accepted

There really is no "limit" to how many calories that a person can absorb in a day. Using them, however, is where other factors come into play, that are very much dependent on the person. For example, during his heaviest training days, Michael Phelps is reported to be consuming between 10-12,000 calories a day. However, if you don't exercise to meet that level of intake, it's going to get stored as fat.

There are going to be a couple of factors that determine how long/far you can go on a hike. The first is fitness. If you only ever train up to 3 or 4 hours for hiking, then you probably won't be able to hike much beyond that before your muscles are just too fatigued to continue. Someone that trains for a 1/2 marathon, for example, probably wouldn't be able to just up and run a 100 mile ultra. If you are unable to keep hiking/climbing at a certain point, compare that to your training and see if it is nutrition or fitness.

As far as the eating/absorption, most people can absorb between 250-400 calories per hour while exercising. Dumping 1800 calories into your system twice a day may not be optimal for you. This is something that you work out in your training, how much you can eat "on the go", and how your body reacts to the large influx of food/calories.

There are numerous calorie calculator and activity cost calculators around on the web, I would take a sample from several to get a "general" guideline for your activity cost, and if you have a 5 hour day planned, calculate your climbing costs for those 5 hours, aim for an hourly intake of a certain percentage of that, and get the rest from your meals.

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I second John P. There must be an upper limit, but it's a lot more than 4500kCal per day. During the tour de france cyclists take in in the region 9000kCal per day. bbc.co.uk/sport/0/cycling/18857794 –  Dani D Jan 3 '13 at 19:31
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