Basically I'm trying to create a combat situation and training where recruits and people on the front line are expected to burn 6,000 to 7,000 calories a day. Now despite how messed up the war is against these foes, which are aliens, they seem to operate themselves on very good conduct given this is a genocidal conflict.

It is the year 2030 and aliens have invade earth for unknown, to most of humanity, reasons. But the war is now a brutal slog. Despite this, as said the aliens conduct themselves, relatively well to us.

One of these is that they allow their human opponents the right to "four square meals a day" during meal times. And surprisingly enough, if you actually give your all the aliens actually take you alive and treat you reasonably well.

Given that their eons more advanced than us the war from their perspective is just a small scale species change/diplacement/breeding. From the human perspectives though its a brutal conflict for the survival of our species.

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    $\begingroup$ This question is perplexing. What is special about 7000 calories? And the second half of the question seems irrelevant. $\endgroup$
    – Daron
    Jul 16, 2022 at 13:28
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    $\begingroup$ are these normal humans or are biologically or cybernetically enhanced, because that is the easiest explanation. $\endgroup$
    – John
    Jul 16, 2022 at 18:16
  • $\begingroup$ Almost normal humans $\endgroup$ Jul 17, 2022 at 5:39
  • $\begingroup$ Data point: Royal Navy Sailors during the age of sail were supplied with around 5.000 calories per day. Source: warhistoryonline.com/history/… $\endgroup$
    – Mookuh
    Jul 18, 2022 at 13:24
  • $\begingroup$ To me it's unclear, do they supply prisoners of war 7,000 calories or do they supply their opponents with meals? If it's PoW, then it's not soldiers (and not combat activities), if it's belligerents then why and how? $\endgroup$ Jul 18, 2022 at 14:21

7 Answers 7


Put them in Antarctica.

butter wagon


At Sea World San Diego there was an exhibit that included a kitchen for Antarctic explorers. It included sticks of butter. Each explorer ate one or two a day to meet caloric needs. The cold means your inner fire needs much fuel.

Two things were found out very early on in Antarctic exploration - that extreme cold makes people feel very hungry and hard work such as that involved in travelling by dog sledge, or especially by manhauling uses a great deal of energy. This energy had to be replaced by eating enough, unfortunately the early explorers didn't eat enough and suffered as a consequence.

We now know that the following Antarctic activities use per day for an adult male:

Manhauling sledges 6,500 calories (27,300 KJ)

Travelling by dog sledge 5,000 calories (21,000 KJ)

Travelling by skidoo 3,350 calories (14,070 KJ)

Working mainly inside buildings 2,750 calories (11,550 KJ)


Bonus is that I cannot remember reading or seeing about a battle set in Antartica.

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    $\begingroup$ A woman who cooked for winter mountaineering told how they would fight over the bacon drippings. Cold is enough. $\endgroup$
    – Mary
    Jul 16, 2022 at 17:53
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    $\begingroup$ mountain climber also often carry large amounts of butter for the same reason. $\endgroup$
    – John
    Jul 16, 2022 at 18:13
  • $\begingroup$ I doubt we'll ever understand this question. Usually posters are hesitant to make such drastic changes to their story as "set it in Antarctica". $\endgroup$
    – Daron
    Jul 18, 2022 at 11:30
  • $\begingroup$ That much Kerrygold would cost a fortune. Two fortunes if you live outside of Ireland and have to import it. $\endgroup$
    – Daron
    Jul 18, 2022 at 11:33
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    $\begingroup$ Those numbers are suspect. The gap between hauling the sled and sitting on it is larger than the gap between sitting on a sled and sitting on a different type of sled. $\endgroup$
    – Daron
    Jul 18, 2022 at 11:34


Military marching is a strenuous exercise. It burns 300+ calories/hour if marching without load and 400+ calories/hour if marching with pack/weapon. Add mud or rugged terrain, and caloric requirements would go higher. If soldiers are required to march several hours in a day, they can require 6,000 to 7,000 calories/day just to keep going.

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    $\begingroup$ Indeed. And then, the challenge becomes to not only march all day long with 25kg on your back, but also to somehow eat the equivalent of ~10 full meals in the process. $\endgroup$ Jul 17, 2022 at 11:20
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    $\begingroup$ @EricDuminil yes, same applies to ultramarathons - one magazine article defined ultramarathon running as "an eating and drinking competition with added scenery and exercise". It's hard to force yourself to keep eating and drinking enough as you get more and more tired. $\endgroup$ Jul 17, 2022 at 17:39
  • $\begingroup$ @KerrAvon2055: Good one! $\endgroup$ Jul 17, 2022 at 18:01
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    $\begingroup$ I can confirm this, in my experience recreational backpacking on mountainous terrain with a heavy pack it's very possible to burn 6,000 kcal/day. Walking 10-12 hours per day is exhausting but do-able during long and not too hot summer days. I found it pretty much impossible to eat enough food and lost quite a bit of weight on my trip. $\endgroup$ Jul 18, 2022 at 20:51

Four Hours Running

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If you look up the diet and exercise routine of Usain Bolt you will see he does something like 4 hours exercise every and 6000 calories.

Of course Usain needs to eat more than normal people because he is bigger than a normal person. Nearly early 2 metres long in fact! So perhaps a smaller person needs to run for 4 hours while carrying heavy army gear.

This also answers the follow-up question of where the food comes from. The aliens air drop pouches of McNuggets with little parachutes onto the battlefield.

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    $\begingroup$ Yep. Like from their perspective their doing a species wide experiment. From humanity's perspective it's a war for survival. $\endgroup$ Jul 16, 2022 at 14:01
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    $\begingroup$ Michael Phelps ate 10,000 to 12,000 calories a day when in training. Backpacking I easily get to 6000 calories in a hard day. Just not that much… $\endgroup$
    – Jon Custer
    Jul 16, 2022 at 14:09
  • $\begingroup$ @ColonizeroftheSun But where does the number 7000 come from? $\endgroup$
    – Daron
    Jul 18, 2022 at 11:04

A few hours long duel in a labyrinth that actually is an arena will be enough to burn a lot of calories. Often in combat the aliens push isolated soldiers in a closed area and then one of them takes on that soldier in a one on one combat. The soldiers must be trained on this kind of duel.

For the aliens they are nothing more than gladiators games. For the men it is matter of survival. The heart pounding at a crazy rate. Move back and forth, left and right, run in circles. Elude the challenger and then catch them by surprise. High on adrenaline all of this will cost a lot of energy.


Marching was already mentioned. But you forget an occupation, ancient world soldiers' were exposed to in large amounts.


Let your soldiers build stuff. Bridges, walls, camps, roads. Some of that they'd need for the campaign. Some not. Building in times before steam or internal combustion engines means a lot of physical work. Probably, all the woodwork would need to be sourced by the army, which means even more lumberjacks. All these are physically exhausting activities, warranting large amount of intake calories.

Make the soldiers accelerates, i.e., the modern body type and size – large men need more calories. Extreme, professional sports or extreme weather conditions would require to reach such intakes.

That's the gist, now let's check the harmony with algebra.

The formula

I've dug up a formula on needed calories based on body parameters and activity:

$$(88.36 + (13.4 w) + (4.8 h) – (5.7 a)) \; c,$$


  • $w$ is weight, in kg
  • $h$ is body height, in cm
  • $a$ is age, in years
  • $c$ is the coefficient for workload type, e.g., 1.2 for no load and 1.9 for heavy load.

Now, let's search for a good parameters. Let's say, the whole army is build from 190 cm tall, 20 years old guys. The top margin of healthy BMI says, they would weight 90 kg. (Let's pretend, it all muscles, not fat.)

These values yield something shy of 4000 calories. Even if we force then to inhuman, bone-crunching work, and raise $c$ to 2.2, that's still only 4600 calories. Too little.

(Notice than while praxis has seen the consumption of the desired amounts of energy, that's not what regular mortals' dietologist would approve of for regular life. So, either make their life really hard, per above. Or – keep reading.)

A normal human does not suffice. So, let's go Warhammer.


Let's take a three meter tall space-marine breed. Scaling up 1,5 m to 3 m height scales up the weight 8 times (because of square-cube law). Let's say, that's 400 kg.

Per above formula, those guys would need more than 8000 calories even idling, and 12000 when heavy working.


So, you either need to work your soldiers to the bone (by forcing them to do hard manual work all the time, by marching insane distances, or by conquering Antartica), or you need larger soldiers.


They wear heavy advanced combat spacesuits which take significant muscular exertion just to wear. (This answer is inspired by the excellent long-running fiction The Deathworlders.)

If this war involves aliens, presumably your soldiers have to be able to fight in extraterrestrial environments. They wear a suit which functions as protection against the vacuum of space and other hazardous environments and armour, as well as being loaded with the typical heavy weaponry, ammunition and equipment that soldiers today carry. In order to function it compresses the body tightly and is also extremely heavy, so just wearing it is a constant full-body workout.


You've got a big problem here--for a normal-mass human the digestive system is pretty much incapable of taking in that kind of energy. Probably the highest sustained-energy activity people engage in is thru-hiking and they generally top out in the 4000-5000 calorie range.

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    $\begingroup$ Olympic rowers go up to 6k/dat. During the Tour de France some eat 8k/day. Strongmen can put away 12k/day. $\endgroup$ Jul 16, 2022 at 21:36
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    $\begingroup$ This answer needs citations for its claims, especially since other answers disprove it. $\endgroup$
    – Drake P
    Jul 16, 2022 at 23:18
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    $\begingroup$ It's easy to eat 300kcal/hour. Eat regularly during 16h, you're almost at 5000kcal. If you're really hungry and know what kind of food you like during exercise, you can add 2000kcal without any problem. For what it's worth, I ate 9000kcal during a 24h relay-race. I basically was either riding at full speed, or eating anything and everything I had brought with me. I never felt stuffed, just happy to refill my body after the effort. $\endgroup$ Jul 17, 2022 at 1:02
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    $\begingroup$ @Loren Pechtel sugars are extremely easy to digest. You only need to swallow, and they go to bloodstream in almost no time. $\endgroup$
    – Alexander
    Jul 17, 2022 at 3:48
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    $\begingroup$ @LorenPechtel I should have written "digest", then. I had to push at full speed during 30min every 2h. I didn't just stay on a couch and eat after the effort, I actually had to go back and use those calories. And I couldn't have done this during 24h without properly digesting what I ate. The nutrition took some planing, but it worked well. As Alexander mentioned, a good portion of it was sugars : 300kcal mixed with some electrolytes in 1l. 1l per hour. $\endgroup$ Jul 17, 2022 at 7:15

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