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I am currently midway through this book, The Company: The Rise And Fall of the Hudson's Bay Empire. It is really good.

One thing that keeps coming up is the amount of rations needed for each explorer, depending on the expedition.

For example, in the 1700s, a guy hires a bunch of rowers to row small canoes, each with about 5,000 pounds of trading material, through Hudson bay tributaries in the Canadian winter ice lands. These rowers each required a ration of "9 pounds of meat" per day! Taking ground beef as an example, this is around 10,000 calories! But, they're rowers... and rowers burn a lot of calories, right? And yet... are they stopping every few days to hunt Seals or whatever? (Seals would probably have even more calories than that because I presume they are mostly fat). If not, this weight could be entirely in dried meat. Which would be almost double the calories!

Later on page 270, an explorer named Thompson in the 1800s is exploring a bit more westward. They are going through an icy forest where there are no animals to hunt. They are chopping down trees every day, to make room for their horses - certainly burning a lot of calories that way. He writes about a companion, "[he is] very gluttonous, requiring a full ten pounds of meat a day". But again here, it specifically says that no animals are available, and they are nearly dying of hunger. So if this dude is eating dried meat or smoked, it could be even more calories! Again, 10 pounds of beef jerky is almost 20,000 calories!!!

What I am wondering is if there is some kind of "translation error" going? Perhaps, right after slaughter, there is more water in the meat than when we buy them at the supermarket today. Therefore, these frontiersmen could be eating fresh meat with a higher water content (and lower calorie metrics) than what the USDA gives for beef. On the other hand, it seems just as likely to me that the meat could almost always be dried? So depending on which way we want to estimate, it seems like they could be consuming anywhere between 5,000 to 20,000 calories! A huge discrepancy! Certainly not the best we can do...

I am thinking is that there are better historical records for other time periods and activities among groups of people. Somewhere along the course of history, there is a log of all the average rations of each soldier, laborer, slave, or prisoner. I'm wondering what the highest averages were for particular groups of people at particular times, if anyone can make an educated guess that can add to my knowledge...

(It is obviously interesting as well to note the type of food they were eating too... Practically all their calories came from meat??)

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    Just as a random anecdote; when I'm on long distance bike trips I spend 10-12 hours per day on a packed bike at fairly high intensity. After a few days I reach the routine where I consume 8,000 - 10,000 calories per day. But I also consume 3,000 - 4,000 calories per day when 'doing nothing' for a day, so there's that.
    – user61951
    Jul 29, 2023 at 23:54
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    But on a more useful note; have you considered that there have been many different 'pounds' throughout history? Are you certain that all mentions of 'pounds' refer to the modern avoirdupois?
    – user61951
    Jul 29, 2023 at 23:55
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    @Chipster, if that was what was happening, the real numbers would be either 20 calories per day or 20 million calories per day. Either option is clearly wrong.
    – Mark
    Jul 30, 2023 at 6:56
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    Remember that until relatively recently, "meat" was whatever one consumed that wasn't "drink". My grandfather came across this, since some of his schoolboys were from a community of Cornish miners in North Wales. Jul 30, 2023 at 11:34
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    Who (other than you the OP) makes the claim that "active frontiersmen ... [ate] 20,000 calories a day"?
    – user54367
    Jul 31, 2023 at 1:14

5 Answers 5

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The 10,000 calorie figure - or perhaps slightly lower - is about right as a ceiling for maintaining muscle mass over months of hard work with downtime only to sleep. Across the centuries, workers with the most physically demanding jobs consumed comparable amounts of food:

19th century: Navvies

My mind goes immediately to the navvies of the mid-19th century, who were famously well-fed on meat due to the demanding nature of their jobs:

navvies had to be strong, fit men – agricultural labourers who joined up could not, at first, stand the pace

They ate quite a generous diet to keep up their strength:

Joseph Firbank (contractor for many railways including the Settle & Carlisle) ‘mentions quite casually that his navvies consumed on average two pounds of meat, two pounds of bread, and five quarts of ale a day

  • Terry Coleman, The railway navvies, 1965, p86.

That's 2304 calories for the meat if it's analogous to ground beef (which is far more likely for grain fed British cows than for hunted game), about the same for the bread, and 2500 for the ale.

However, this was not sufficient for the navvies:

They were also known for poaching fish and game...it’s highly likely that the navvies supplemented their diets by poaching.

It's hard to say whether they poached due to hunger or simply for variety in diet and the thrill of something to do, but these hard-working laborers scarfed down 7500 calories and still had an appetite for more. I can see explorers, without fixed working hours and burning additional calories shivering in the brutal Canadian north, wanting to eat more than that to sustain themselves.

Antiquity: Pyramid builders

Speaking of beer, the pyramid builders drank about the same amount - five liters (just over 5 quarts) per day. It's hard to say how Egyptian beer, sweetened with honey, would compare calorie-wise to what the navvies had, but our attempts to recreate ancient ale clock in around the same - 300 for a pint of Midas Touched compared to 250 for a typical ale.

Along with the beer, the workers received ten loaves of bread and somewhere between half a pound and a pound of meat per day (spreading the 4000lbs figure across 4-10,000 estimated workers). Given the monumental (ha!) costs of building the Pyramids, I can't imagine these workers would be fed so generously if they didn't need the calories for their work.

Late 20th/ early 21st century: Rangers and survivalists

Another highly standardized diet is the one fed to soldiers. Since the 80s, the American soldier's diet has been precisely tailored for the demanding activities that soldiers do, and consists of three daily "meals, ready to eat" - under 4000 calories.

However, your explorer's routine is probably closer to the experience at Ranger school:

Typical ruck marches with 50- to 80-pound backpacks will burn 500-700 calories per hour. Place that level of work into an 18- to 20-hour day, and you expend roughly 10,000 calories in one day.

According to this source, Ranger trainees get 2 MREs per day - 2500 calories - and lose 20-30 pounds after two months. Needless to say, that is not a sustainable pace for explorers who may be on expedition for seasons or years.

We have a bit more insight into the calorie demands of survival situations through the reality show Alone. Towards the end of the competition, the contestants typically eat very little and it shows - one contestant lost 80 pounds in 2 months, equivalent to burning 5000 calories per day just staying in one spot. For a rower - having to work all day on top of hunting and putting up/tearing down the campsite - the calorie demands would be considerably more.

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    Excellent. You might consider adding a section o Michael Phelps 10,000 Calorie / day diet. His morning warm-up was a quick five mile swim, followed by breakfast (3 fried egg sandwiches, 3 chocolate chip pancakes, and a five egg omellette, French toast, grits and two cups of coffee) before heading out for the heavy training of the day. Jul 29, 2023 at 16:59
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    That's a good callout; but I'm reluctant to refer to one specific person's high intensity training regimen as I couldn't say whether the workload and metabolism of a top 0.00001% modern day athlete would be comparable to a typical worker.
    – SPavel
    Jul 29, 2023 at 17:20
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    Whatever. +1 for mentioning shivering. Shivering burns 400 calories an hour. In the night when it got super cold, they must have been burning tons of calories even while sleeping! Jul 29, 2023 at 23:53
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    @nickcarraway, they're probably not going to be actively shivering. With a group of people, you've got a number of options for keeping warm, ranging from elaborate shelters to simply huddling up in a pile.
    – Mark
    Jul 30, 2023 at 7:06
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    @Michael: Sure does. The green book (old version of Mountaineering, Freedom of the Hills) says you can't eat 5,000 calories per day and expect to retain it. And so, we get the mountaineers' diet: eat what you want, climb three mountains per week. Adjustment is probably possible but it's not getting anywhere near 10,000.
    – Joshua
    Jul 31, 2023 at 3:56
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A lot of information concerning the caloric intake of 18th century travelers in the Canadian wilds can be gleaned from a journal article published in Arctic Anthropology in 1993, "Always with Them Either a Feast or Famine": Living off the land with the Chipewyan Indians, 1791-1792, by June Helm. This can be read at JSTOR within the free monthly articles alloted. The article examines in detail the foodstuffs mentioned in the journals of Peter Fidler, a Hudson Bay Company employee who was 'embedded' with a group of Native Americans over the winter of 1791-92.

The abstract sums up what was the average consumption of the group by both weight and calories (the article goes into full details on what was consumed and how the calorie figures were arrived at)(emphasis mine):

ABSTRACT
Peter Fidler's record of food kills by his Chipewyan companions in the boreal forest south of Great Slave Lake through the winter of 1791/92 is combined with calculations of percentages of consumable tissue and kilocalories from the prey animals— bison, moose, and beaver— to yield a high-low range of edible tissues of 6.89-6.15 lbs per person-day and 5780-5140 kcal per person-day.

So this article gives some related information and shows that over a winter period the food intake for the party members was roughly 6.15-6.89 lbs. per day, with the calories come in at 5140-5780 kcal per person per day.

If we divide that out we get about 836 calories per pound of wild meat. At the "9 pounds of meat" per day ration allowance you mention from the original source, then we should expect your rowers were consuming roughly 7524 calories per day (though some variation depending on what game they consumed would of course be expected), not nearly the 20,000 from the title question.

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  • The 'feast or famine' remark refers to the fact that hunters often go for days with very little food and so tend to gorge when the opportunity arises. This shouldn't be seen as a typical daily intake.
    – DrMcCleod
    Aug 1, 2023 at 15:30
  • Yes. The article however goes into detail calculating out the food collected during a large timeframe, and does the calculations from available historical data from Fidlers actual extensive journal entries. The value presented is an analysis/average of this multi-month historical data set. The purpose of this answer is to show an actual historic correlation to what type of calorie values might be expected from wild game taken and consumed during this time in history. It gives a real value based of real historic data to calculate from.
    – justCal
    Aug 1, 2023 at 15:42
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Certainly not for long

Take the Race Across AMerica for example. One of the most grueling endurance competitions in the world. This Case Report says the 4th place finisher in 2003 burned 15 100 - 23 280kcal per day (17 965kcal average). This would put him close to your 20Mcal estimate. However, that’s a modern world class athlete, doing it for 9 days with barely any sleep and certainly not something they or anyone else could keep up for long. Other fun facts: The athlete from the report “only” ate ~10Mcal per day and therefore lost 5kg of body weight in those 9 days. He also drank between 10 and 19l of water per day.

An “Iron Man” type triathlon competition burns 11 009kcal in 12.5 hours.

As for a sustainable energy consumption: World class long-distance cyclists ride up to ~700km/week during a year. Roughly estimated that’s 2000–4000kcal/day. If you add basal metabolic rate that’s less than 6000kcal/day.

I do think that cycling is a good exercise to pick for an upper boundary. I don’t think there is any other exercise humans can keep up for so long at such a high intensity. Running, rowing, hiking/mountaineering, cross country skiing or just general hard physical work (e.g. moving heavy things) might come close in perfect conditions.

Another limitation is the human digestive system. Eating 20Mcal in 16 waking hours would mean you have to eat 1250kcal every single hour. Even half of that is already a big challenge, especially when it’s not just simple carbs and fats.

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  • As a bit of a long distance cyclist myself, of course I'm inclined to agree, but then I remember ultra-runners. I vaguely recall reading that the maximum sustainable consumption (and effort) is approximately 3.5× BMR, but I've just checked Bicycling Science by Wilson and couldn't find it, so I can't remember where I saw it.
    – Chris H
    Jul 31, 2023 at 16:44
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    @ChrisH: Yes, ultra-runners have insane endurance and injury resistance. The craziest competition is probably this race with the record at 40 days for 5000km: en.wikipedia.org/wiki/Self-Transcendence_3100_Mile_Race Still, that’s probably less than 13h of slow running per day, consuming maybe 6500kcal (+BMR).
    – Michael
    Jul 31, 2023 at 17:10
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Just one example I remembered (as the question-asker):

According to this documentary, Victorian industrial workers burned roughly 5,000 calories a day. This helped fuel a bread and bakery industry.

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The paper Extreme events reveal an alimentary limit on sustained maximal human energy expenditure, Thurber et al (2019) answers a related but slightly different question, namely what ‘total energy expenditure’ (TEE) can humans sustain, as both a number of kcal, and as a multiple of Basal Metabolic Rate (BMR). That's the energy expended, as opposed to the calorific value of the food consumed.

There's plenty of detail there, but the paper concludes, inter alia,

  • As the endurance event gets longer, the TEE per day decreases – ie, you can only keep this up for so long – and seems to converge towards a low-ish upper limit on the body's ability to convert food to activity, that can be kept up more or less indefinitely.
  • And it indicates, more or less in passing, that the most hardcore, ultra-endurance human activity is to be pregnant for nine whole months.

From the discussion:

The relationship between SusMS and duration flattens out at ~2.5× BMR (Fig. 1B), suggesting a metabolic ceiling for habitual metabolic scope (often termed “physical activity level”) in humans. Prolonged expenditure above this metabolic ceiling (~2.5× BMR) requires consuming energy reserves and is not sustainable indefinitely.

That is, though humans can sustain much larger figures (~10 x BMR) for short periods, there seems to be a robust limit on how much they can sustain indefinitely, without losing weight. That appears to mean that, even if workers consume many calories, there is an alimentary system limit on how much energy the body can extract from this long-term. Figures 1b and 3b seem illuminating, here.

Or, focusing on the original question, it appears that, even if these frontiersmen managed to get 20 000 kcal/day down their throats, it doesn't follow that their guts managed to turn all of that into physical work, beyond an initial period (that is, and heading towards the scatological, they might have made a lot of dung beetles very happy).


Terms:

  • Basal Metabolic Rate.
  • ‘Total energy expenditure (TEE) is composed of the energy costs of the processes essential for life (basal metabolic rate (BMR), 60–80% of TEE), of the energy expended in order to digest, absorb, and convert food (diet-induced thermogenesis, ~10%), and the energy expended during physical activities (activity energy expenditure, ~15–30%)’ (from 10.1186/s40798-017-0076-1, which has further information about this sort of question).
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    “And it indicates, more or less in passing, that the most hardcore, ultra-endurance human activity is to be pregnant for nine whole months.” A quick internet search says that pregnancy only increases energy requirements by a few hundred kcal per day.
    – Michael
    Aug 1, 2023 at 6:53
  • I'm not a biologist, but I presume the apparent discrepancy between the calorie figures (they quote ‘only’ 6200 kcal/day for a marathon-per-day) is down to a difference between the calorific value of food (which is measured by burning it, I think, thus a physics measurement) and the amount of work the body can do by metabolising it (a biological measurement). The point of the paper seems to be that (a) there is a limit to the metabolic increase one can sustain long-term (rather than briefly), (b) that it's smaller than one might think, and (c) it happens to be about the same as being pregnant. Aug 1, 2023 at 14:23
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    I can’t find where your linked paper got its data from for pregnancies. They somehow assume that it doubles metabolic rate. In this study energy intake of pregnant women with normal BMI went from 2434kcal/day to 2904kcal/day in the 36th week of pregnancy. Seems like a much more reasonable increase (though the absolute number is surprisingly high for non-athletes) sciencedirect.com/science/article/pii/S0002916522039685 Energy Expenditure went from 2434kcal/day to 2693kcal/day.
    – Michael
    Aug 1, 2023 at 16:24
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    They cite references 24 and 25 in their paper. It's true that there doesn't appear to be the simple link I'd guess between calorific intake and multiple of BMR, but (hell, this is biology!) I shouldn't be surprised that the link is more complicated than I'd expect. The relevance is that the paper suggests that the OP's very high numbers for intake might indeed be overestimates (as suspected, if they were based on reported food-bills). Or perhaps that even if the 'rowers' consumed that many calories, they might not have metabolised them in fact. But I'm not a medic. Aug 1, 2023 at 16:59
  • (When I rejected the edit, I expected I'd be prompted to explain why). That's a great comment to add – thanks (though I can't see the figure 9900 in the paper) – but what seems to be key to the paper is that the effect they describe is independent of the activity, but depends more on the duration of the activity (though the arctic trekking is clearly long-ish term). I'm even inclined to remove my first bullet point, since it might distract from this observation. It's interesting (but... unsurprising) that the link between calories consumed and expended is much more complicated than I'd expect. Aug 2, 2023 at 9:47

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