Did active frontiersmen really eat 20,000 calories a day? How does this compare to other highly-active people in recorded history?

Question

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??)

Answer 1

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.

Answer 2

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.

Answer 3

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.

Answer 4

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.

Answer 5

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).

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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).