UKC

I've just finished Herman Pontzer's 'Burn' - he was one of the pioneering researchers who found that whether you run marathons, are a Hadza hunter- gatherer, or a sedentary office worker in London, once we account for body size and composition,  we all have roughly the same daily energy expenditure (two people of similar build and size can vary by 500kc a day)

It's an extraordinary read with some really interesting evidence (the main finding has been found by different teams both across populations and within populations):

"Our metabolic engines shift and change to make room for increased activity costs, ultimately keeping daily energy expenditure within a narrow window. As a result, physically active people—whether it’s hunter-gatherers living today or in our collective past, or people in the industrialized world who exercise regularly—burn the same amount of energy as people who are much more sedentary....

....Metabolic response to increased exercise, the phenomenon we see with physically active groups like the Hadza or in Westerterp’s half-marathon study, is less well studied but seems to follow similar logic. With the muscles demanding a much larger share of the business’s energy and draining fat reserves, the Darwinian manager acts to rebalance the budget. In the immediate term, hunger is increased in order to match intake to expenditure. If high levels of daily activity persist for weeks or months, though, other changes are made. Other systems, including reproduction, immune function, and stress response, are suppressed, making room in the budget for greater activity costs."

Great to see two people down-voting a scientifically established fact. There's a psychology learning point here, not just one on metabolism. 

Really?  If you're too thin-skinning to ignore a couple of downvotes it'd probably be better to just switch them off. 

Of course you can't really know what the odd downvote signifies - it's just as likely that a couple of folks think this subject is a bit of a 'groaner' just now, on account of having been done to death just recently on this thread:

https://www.ukclimbing.com/forums/walls+training/so_regular_exercise_doesnt...

And then continuing onto this thread when that one auto-archived:

https://www.ukclimbing.com/forums/walls+training/so_arguing_on_ukc_doesnt_b...

https://gsas.harvard.edu/news/colloquy-podcast-why-exercising-more-may-not-...

It's not that he's not keen on them nor called them hocus pocus. He just stated that energy is energy. He did say that consumption of protein vs carbs will have different effects on the body.

I'd heard this on the radio when Chris Van Tuleken was promoting his new book Ultra processed people. I remember thinking, really? Especially as he said the spare calories for less active people went into detrimental things like 'inflammation'. it didn't sound very scientific! 

Thanks for citing the research it must have been based on. 

Just been thinking about this. It's not that revolutionary or discongruent with orthodoxy, is it?

We all have an appetite, turns out that's pretty consistent. If you are physically active, you'll stay slimmer. If you are sedentary you probably wont, and your health may suffer in other ways.  And if you exercise a lot but don't fuel it appropriately that can also be detrimental for your health, e.g. lowered imunity or REDS. 

Perhaps the main thing is putting a downer on exercise-as-weight-loss. No you haven't earned  your latte and muffin just becuase you went to the gym. 

+1 for the eyeball rolling/groaning crowd.

I accept that the body does adapt marvelously in all sorts of ways to external pressures (we wouldn't be the third most highly evolved species on the planet if it didn't). But this sort of "extra exercise doesn't make you lose weight because it doesn't use more energy" guff is, for me, in the same realm as perpetual motion machines or flat earth or vaccines give you telepathy theories - it can all be debunked with a GCSE level understanding of physics.

Looks like the eyeball-rolling crowd misunderstand what is interesting with the research.

If you are not surprised that a sedentary office worker and a hunter gatherer living an active life living off the land both expend the same energy daily (adjusting for age, body composition, size), and that this would also apply to an arctic explorer or olympic athlete (allowing for a period for adaption to occur), then I'd recommend the book. 

Moreso, if you think doubly-labled water method of determining energy expenditure is guff. There's likely a Nobel in it for you.

Ignoring the rest of your post which was thoroughly done to death in the other thread(s)..

Where does that come from?  What on earth does "most highly evolved" mean?
(And what are the first and second "most highly evolved" species?)

No one poster speaks for the 'crowd'.  Henwardian's eye-rolling/groaning is clearly a tad hypocritical whilst trotting out the same old "calories in -vs- calories out" chestnut with the same breath, as if that somehow contradicts Pontzer's results.

I have no problem accepting the counter-intuitive results of Pontzer's research that I read whilst following the other two threads, but struggle to believe this bit and have seen no research that supports extrapolating to this extreme.

Is it specifically addressed in the book?  What research has Pontzer (or anyone else) done to back that up?  That extreme amount of activity is well beyond the daily lives of the Hadza for example.  Got a link to something that's available online?

How long would that period of adaption be?  Gary MacKee didn't get there in his year of daily marathons it seams, eating 5000-odd calories a day throughout.  And apparently Steve Redgrave didn't get there over a couple of decades, regularly consuming 7000-odd calories while training hard without gaining weight.

1. Homo UkCeeus Armchairus Opinionus

2. Dolphins

3. Homosapiens

Assuming an adult male consumes 2000kCal a day, but runs a marathon every day, burning 3000kCal in the process, what happens?

Yes they will rest and probably sleep more to conserve energy and recover, but how do they not lose weight over time?

Equally, why are Arctic Explorers bothering to eat 7,000kCal a day.

I see deepsoup has essentially asked the same questions, but in a more intelligent way. I’m interested in the more extreme examples, because I do see those contradicting what you are saying. 

Yes - most of your questions are addressed in the book.

I'm sure it has, but seeing as I wasn't in those threads (that I remember), I thought I'd use this opportunity to put my 2 sense in.

Dolphins and mice of course

Ranulph Fiennes' book on manhauling sleds across the antarctic/arctic is a great proof of concept there - they eat about 5k calories but still lose 8 or 10 stone or something over a few weeks.

Yup.

Scott's team basically exercised themselves into starvation and ultimately death, starting with the biggest fella, Seaman Evans.  I guess that's quite an outlier though. 

I intuitively share your doubts about whether this observation could possibly extend to the more extreme cases. But if the argument is that the body adapts over a long timescale to your typical lifestyle, then an Arctic explorer needing to take in more energy while pulling a sled isn't necessarily a counterpoint to that because even the most extreme explorers don't live that lifestyle constantly.

A specific example is given in the book based on the work of Klaas Westerterp. A group of sedentary women trained for a marathon. After 40 weeks of training their daily energy expenditure was only about 120 kcal higher. "These women went from never exercising to running 25 miles per week, fit enough to run a half-marathon, and their daily energy expenditure was essentially the same as when they started. Men in the study showed similar results."

It's not that they don't lose weight - more that we don't necessarily burn energy in a linear fashion through the day or across the week when we switch things up - there's a transition period to constrain energy expenditure back within its window. Fat use is used to fuel a smooth transition until several other metabolic processes can be up/down regulated to 'fuel' the exercise so your total expenditure WILL eventually return to the same as before; your energy use is constrained, to a point that "meaningful changes in daily energy expenditure are extremely difficult to achieve through exercise".

it's more what the research is saying!

Arctic explorers maybe, but Steve Redgrave trained consistently for 5 Olympic cycles. I don’t know how many calories he consumed, but I am pretty sure it was more than 2000 a day. 

Pontzer notes the Midwest 2 study where participants were assigned to either 2,000 or 3,000 kcal of supervised exercise per week over 10 months. That’s like running 20-30 miles per week for a 150-pound person. Daily energy expenditure increased 220 kcal/per day on average (below the 285 - 430 kcal/day increase expected from such a regime). Average weight loss was 10 pounds and there was no difference in average weight loss between the 2,000 and 3,000 kcal/day exercise groups, suggesting the dose of exercise had little effect on weight. For 34/74 participants who completed the study achieved ZERO average weight loss.

From Pontzer's literature review yhis is a common outcome, the longer a study lasts, the less that weight loss meets expectations. It's certainly the outcome of shows like The Biggest Loser.

Your mistake here is ignoring the fact that energy expenditure needs to be 'normalised' for things like size and body composition. No one is saying that the same absolute energy expenditure applies to everyone. 

IIRC,  it's worth adding here Pontzer's observation that athletes are particularly vulnerable to infection around peak training due to down regulation of metabolism dedicated to their immune system.

Also of note is research he points to regarding Olympic athletes' lower stress response to high stress situations (like public speaking). Sedentary people tend to have a higher sress response (metabolically expensive), but the allocation of metabolic activity to stress amongst athletes is necessarily lower in a constrained system  due to the demands of their training. 

As above,  you're misunderstanding the constrained energy expenditure model. Once ADJUSTED for body size and composition Redgrave falls within expectations (Pontzer actually discusses Michael Phelps or Katie Ledecky) - albeit at the upper end. Think in relative NOT absolute values.

Pontzer goes on to discuss the upper limits of calorie absorption suggesting that modern Olympic athletes may be "distinguished as much by their remarkable guts as their ferocious strength".

25 miles a week is pretty low mileage for marathon training. It’s 400kcal a day, well within what you would expect the body to be able to adapt to with energy conservation elsewhere. It seems the research doesn’t disagree with me.

Mo Farah consumes around 3,500kcal a day, but only weighs 58kg.

Pontzer mentions research on the Race Across the USA (essentially a marathon a day, 6 days a week for 140 days), "[in the] first week of the race, the runners burned exactly what we’d predict if we added the cost of a marathon to their prerace daily expenditures... One week isn’t enough time for the body to adjust to the new workload—a marathon per day—and so the cost of that activity was simply added to the body’s usual, prerace energy budget. [The] runners were averaging an incredible 6,200 kcal per day. But by the end of the race, 140 days later...runners were burning 4,900 kcal per day—still impressive, but a 20 percent decrease from the first week of the race."

So, importantly not 2,500kcal or less, like someone with a sedentary lifestyle or modest amounts of exercise.

6,200kcal is very high even for a marathon day. That probably needs some more research.

Don't ignore/forget that the constrained energy expenditure  model requires adjustment for size, age, gender and body composition. That done, the athlete will fall within the boundaries of the model.

Possibly - but I'll reiterate that the body takes time to adjust to the 'new normal '.

I'd recommend the book. It's a demanding read because it challenges intuition but it's a really interesting read.

I’d like to test this, because this statement is doing a lot of heavy work and isn’t really supported by what I know of elite athletes and keen amateurs.

Absolutely - i mean, that very point is everything underpinning his model.

Pontzer doesn't go in to the process of 'normalising' the data in 'Burn' - one assumes it's in his paper. But he does present plots of daily energy expenditure (which I can't paste here).

But it does, to a point, after you've normalised for size and body composition.  Pontzer says so, based on his research with the Hadza, and in the podcast linked above by wbo2 (this one: https://gsas.harvard.edu/news/colloquy-podcast-why-exercising-more-may-not-... ) explains clearly why that is in terms of 'economics'.

In that discussion he explains that even in the Hadza, the calories they burn through exercise during their daily lives are still only a fraction of the overall calorific 'budget' of their bodies for the day.  And that what happens when an American couch-potato increases their daily exercise to rival a Hadza hunter-gatherer is that their body compensates by cutting the 'budget' for other metabolic processes within the body.  Thermoregulation, the immune system, digestion - blah di blah, processes over which we don't have conscious control.

You seem to be extrapolating way beyond that, to say that it also makes no difference when the daily amount of exercise is increased to the extreme - to the point that it is no longer less that the body's 'budget' for autonomic processes, but goes way beyond that.  (Twice or more what a person of similar size and body composition would ordinarily consume in a day burnt on the day's exercise alone.)

Not having a copy, I can only take your word that Pontzer also says this in his book, though he doesn't seem to have said so in anything available online that we can see, and this assertion would not seem to be supported by any of the research of his that we can see - certainly not his work with the Hadza.

So there's that.  To be blunt, I think either you are misunderstanding Pontzer's book, or I am misunderstanding you.  Because if you're saying what it seems to me that you're saying, I don't believe you.

But then on the other hand, these extreme cases of an Olympian athlete in training or a polar explorer dragging a pulk for mile after mile across the ice are irrelevant anyway.  Anyone noting that exercising to such an extreme degree does indeed significantly increase the body's calorific consumption and looking to seize on that as a 'gotcha' to say that Pontzer is wrong is clearly missing the point. 

The interview with Potzner linked above,  doesn't say the energy budget remains constant. He says if you do more, appetite increases, so is he not saying that a polar explorer consumes more calories? But perhaps not as many as might be expected. 

This one.

above https://gsas.harvard.edu/news/colloquy-podcast-why-exercising-more-may-not-... 24

Look again - he clearly does:

"And in fact, when you account for things like body size, fat percentage, age, no matter how you want to sort of slice it, there's actually no difference at all in daily energy expenditure between Hadza men and women and adults in the US and in Europe and other industrialized populations. So, a total shock. They are 5 to 10 times more physically active, but there is no discernible difference in the total calories burned per day."

Well, he is saying that a hunter gatherer and a sedentary US office worker have the same energy expenditure.  He is not saying that is the case for a polar explorer, who might have a much greater requirement.

You are misunderstanding what i am saying. Continually. Best you read the book.

As above, "I'll reiterate that the body takes time to adjust to the 'new normal '."

There is one section of the book that reveals a bit if his methodology:

"When we put the daily energy expenditure measurements together with the data on weight loss, we found that every athlete (and pregnant mother) in our dataset was taking in the same amount of energy per day. Across the board, from the Antarctic trekkers to elite distance runners, their bodies were absorbing about two and a half times their BMR (just as we did with energy expenditure, we calculated energy intake as multiples of BMR to account for differences in body size). All of the energy expenditure above the two and a half times BMR intake limit was coming out of their fat stores, which is why athletes above that level of expenditure were losing weight."

The 5 to 10 times daily energy expenditure through exercise for the Hadza seems such a dubious claim to me. Firstly 5 to 10 times is a very big range, secondly the figures that I have seen suggest it is actually around 2.5 times.

In amongst all the confusion in this thread, I have gone back to the opening post and the above quote from the book.  Sounds far from scientifically definitive to me, especially from an author proposing a thesis

A factor of 2 isn't all that much really is it?  I think some of the Hadza do twice as much daily exercise as others, let alone sedentary American office workers.  (Typically the Hadza men do much more than the women as they spend much of their day covering a lot of ground whilst hunting).

I'm not sure about the figures - I looked into it while reading around the first thread and it didn't seem unreasonable to me at the time.  Can't be arsed to go back and dig through it again tbh, but I'm pretty sure the data is available through various links in the other thread(s).  It isn't paywalled or anything like that.

Ha.  You say that like it's my fault.  Perhaps you could find a way to express yourself more clearly.

Lets try to clear up one thing though..

Pontzer has shown that a sedentary western person who increases their daily exercise to something comparable to a Hadza hunter gatherer will not find that their overall daily calorie expenditure increases correspondingly.  (Or indeed at all.)  I think we agree about that.

You seem to be saying that the same holds true for a person who increases their daily exercise further, much further, and well beyond the amount built into the daily life of the Hadza.  For example by running a marathon every day, or setting out on a polar expedition.  Are you saying that?  If not, then what?

I might well do that.  But then again I already have a pretty big stack of unread books, so y'know..

How much time?  Gary McKee doesn't seem to be much bigger or have more lean muscle mass than I do, but he was still eating at least double my total daily calorie intake at the end of a solid year of daily marathons without gaining any weight.

I have read the book.  It is counter-intuitive but fascinating, and certainly convincing enough to make me re-think my prior assumptions.

Pontzer's research is rigorous and peer-reviewed, so instead of arguing that the OP has got it wrong, I suggest people try reading the book for themselves.

As for those saying it's counter to GCSE physics, I have a degree in physics.  But Pontzer's research isn't about physics; it's about biology.  That's the point.

It has been peer reviewed yes, but the sample size is less than 20 for his hunter gathers and well under a thousand for his western participants.

The authors other paper that looked at the effects of physical activity and energy needs also just required participants in the study to report their physical activitie levels using an accelerometer wrist logger being worn for more than 68% of the duration of the study.

It's some stretch to use this data to make large observations on daily energy need across the global population, but he can write whatever he wants in his book. Looking at the number of citations his papers received it's not going to make much difference to his academic work.

​​

I certainly agree with this sentiment so far as Pontzer's work with the Hadza is concerned, and indeed it is.  I'm fully prepared to accept the surprising result that exercising more, within the bounds of a reasonably normal lifestyle, will not result in me burning more calories over the medium to long term.  (Actually I don't find it as counter-intuitive as all that because my own anecdotal n=1 personal experience directly bears this out.)

However the OP seems to me to be extrapolating beyond the kind of increase in exercise that is compatible with a reasonably normal western lifestyle (or even the lifestyle of a hunter-gatherer), to claim that it holds true for a person doing something much more extreme.  Like undertaking a polar expedition or running a marathon every day.  (During which time they may consume 5000 calories or more per day for months on end without gaining weight.)

That's the bit I'm having trouble with.  Does Pontzer say this is the case in the book?  I find it hard to believe that he does, but if so what research does he cite to back it up?

Only one post above says Pontzer's results run counter to GCSE physics, and tbh I think it's rather more to the point that that post was just plain wrong.  Clearly they don't.  And biology in general never does.

Interesting thread and really good summary post.

I think the below quote is the key bit that the OP hasn't really been able to explain/justify.

Gary McKee/Mo Farah/other similar athletes maintain the same weight over a long period of time, while eating considerably more than sedentary people of the same weight. Unless the 'time to adjust' referenced by the OP is of the order of >10 years I can't reconcile this with the position laid out in the OP.

Sorry - I just realised that this was a reply to me, not the OP.   Yes, I agree.

Ah - here we go!  We're conflating different things here.
https://www.science.org/content/article/study-marathon-runners-reveals-hard...

The 'time to adjust' thing that the OP refers to comes from an entirely different study (nothing at all to do with the Hadza) which measures the basal metabolic rate of athletes before undertaking endurance challenges, and then their calorie consumption during the event.

Pontzer is most definitely not saying that those athletes consume a similar amount of calories to sedentary people.  He's saying that their consumption is ultimately limited to a maximum of about 2.5 times that.

In the short term it seems that humans (and most mammals) can process up to about 5x their BMR, but that as their year of daily marathons, intense athletic training, polar expedition etc. goes on that drops to a 'plateau' of about 2.5x their BMR after a period of about 20 days. 
(So Gary McKee's 5000 calories a day would seem to fit that quite nicely.)

It doesn't say what happens if an athlete eats more than 2.5x BMR worth of calories in the longer term, but presumably if the digestion is maxed out the excess just goes right through.  (Hence polar explorers cramming in as many calories as physically possible yet continuing to lose weight.)

Edit to add: 
Here's the paper:  https://www.science.org/doi/10.1126/sciadv.aaw0341

I’m quite cynical, because some of the data doesn’t seem quite right to me, at least in the way it has been presented to me. However, I bought the book this lunchtime and will read it fully before the subject inevitably comes up again in a few months.

Continually. 

https://www.ukclimbing.com/forums/walls+training/burn_energy_expenditure-76...

"Across the board, from the Antarctic trekkers to elite distance runners, their bodies were absorbing about two and a half times their BMR (just as we did with energy expenditure, we calculated energy intake as multiples of BMR to account for differences in body size)."

In my N=1 experiment during COVID I did a stupid virtual challenge where a team of us clocked up miles going "round the globe".  Amongst other things this involved sitting on a static bike under my stand up desk for quite long periods of time.  With no changes in diet I lost about 6kg, which went back on when I stopped.  The calories burnt weren't tonnes either, just enough to gradually lose the weight over a few months, so this book's assertions don't ring true. 

I can't find the reference, but the Stronger by Science podcast referenced a doubly labelled water study that looked at the impact of exercise on calorie deficit, and concluded that about 70% of them actually "counted".  Of course as mentioned above a lot of these sport and nutrition studies have very small sample sizes, non-representative populations (basically students you can pay to participate), etc.

Hm, yes.  Well, I certainly do feel pretty silly now.  Still, at least I did manage to work it out for myself in the end eh?

I can't imagine now where I got the ridiculous idea that you'd suggested the book claims a polar explorer expends the same sort of energy daily as a sendentary office worker or a Hadza hunter gatherer.

Oh - unless perhaps it was this:

https://www.ukclimbing.com/forums/walls+training/burn_energy_expenditure-76...

"If you are not surprised that a sedentary office worker and a hunter gatherer living an active life living off the land both expend the same energy daily (adjusting for age, body composition, size), and that this would also apply to an arctic explorer or olympic athlete (allowing for a period for adaption to occur), then I'd recommend the book."

Thanks - interesting stuff and good effort finding it! Good to know that Pontzer isn't saying what I interpreted the OP as saying.

I wonder if it would be possible to take advantage of this 5x short term limit vs 2.5x long term limit in training. You could maybe stop your activity of choice for a short period, to reset back to being able to access the 5x short term limit again.

These two quotes from you don't really seem to agree with each other:

"Across the board, from the Antarctic trekkers to elite distance runners, their bodies were absorbing about two and a half times their BMR (just as we did with energy expenditure, we calculated energy intake as multiples of BMR to account for differences in body size)."

"If you are not surprised that a sedentary office worker and a hunter gatherer living an active life living off the land both expend the same energy daily (adjusting for age, body composition, size), and that this would also apply to an arctic explorer or olympic athlete (allowing for a period for adaption to occur), then I'd recommend the book."

The first implies that people doing lots of exercise would use more energy than a sedentary person. The second implies that they wouldn't. Any thoughts?

I remain confused.

And continually - "If high levels of daily activity persist for weeks or months, though, other changes are made." (from the opening post).

From real life experience... he's in love with himself being the great renta-expert on everything under the sun including fields in which he has no specialism in. Once the charisma wears off you might view him in a different light. Be cautious of his pontifications in areas other than infections disease 

Tldr:   he's a c*ck

Pretty weak tea, Shani.

You're being snarky with me for having been confused about what you were saying.  Primarily because you clearly did misrepresent what the book says in your post at 16:05 yesterday.

You ignored a couple of opportunities to correct my error, in one case replying to my post but ignoring the question in it in which I specifically asked you to clarify whether or not you meant to say what you seemed to have said.

But I guess clearing up the confusion would have involved you having to admit that you'd made a mistake, which seems to be difficult for you.  Ah well.

Just to be crystal clear, since apparently I've been struggling a bit to keep up in this thread...

This is Chris Van Tuleken, not Herman Pontzer?

For a groaner I'm surprised you're balls deep in this one.

The book seems pretty clear that whatever the pursuit, the body will adapt to align with the constrained energy expenditure. This takes time - whether the arctic adventurer stops before his body gets 'there' is the key point, but that is the adaption its on course for. This is why the Hadza are way more active but there energy expenditure matches that of the sedentary (with due adjustments).

Sorry.. it was aimed at Dr Chris V T

I know, ridiculous isn't it.  I'm not surprised though, just cant help myself sometimes.  Bit disappointed maybe..

Oh, ffs - so after all the snark about me apparently misunderstanding you, it turns out you are conflating the two things after all!

No.  The arctic adventurer's body is in no way "on course for" an "adaptation" in which it consumes about the same amount of calories as the Hadza hunter-gatherer or the London office worker, and I do not believe you for a second if you're claiming that Pontzer says otherwise in his book.

Here's the paper from his research with the endurance athletes/arctic explorers etc. again:
https://www.science.org/doi/10.1126/sciadv.aaw0341

And here's the graph from that paper - it is very obvious that the extreme athlete's calorie consumption is trending towards approximately 2.5x BMR, not 1x BMR. 
(BMR being what it would be for the same person at rest, or perhaps doing up to about the same amount of exercise as a Hadza hunter-gatherer.)

Here's the article talking about that paper in more layman's terms again: https://www.science.org/content/article/study-marathon-runners-reveals-hard...

Pontzer is abundantly clear there that what ultimately limits the calorie consumption to approx 2.5x BMR is that it is the maximum possible rate at which the human body can absorb food and convert it into energy over a sustained effort much beyond about 20 days.  He says: "We ended up plotting out the very limits of human endurance, the envelope for what humans can do."

He's equally clear on how the Hadza consume the same calories as the London office worker, and there he talks about an entirely different mechanism.  For example in the podcast linked upthread:

https://gsas.harvard.edu/news/colloquy-podcast-why-exercising-more-may-not-...

"But actually, even if for someone in the Hadza community, most of the calories burned every day are burned on other stuff. They're burned on immune system and on just the basic processes of homeostasis, keeping your cells alive, reproductive system, nervous system.

All of these systems that we aren't even really aware of are actually where you spend the bulk of your calories. And so, what we think is happening is the Hadza and other really physically active populations, they're spending a bit less on those other processes to sort of make room for the physical activity. So, there's no magic here. The laws of physics remain intact, undefeated."

Obviously, obviously, that can only hold true while the majority of the calories burned in a day are burned on "other stuff", as Pontzer says, besides exercise. 

As you increase the amount of exercise from sedentary office-worker levels, up through hunter-gatherer levels and then beyond to the insane extremes of a polar expedition there inevitably comes a point where it is no longer possible for the body to compensate for that and maintain a roughly constant overall energy 'budget' by trimming its expenditure on other processes.  There is only so much it can trim from the 'budget' for thermoregulation or the immune system, because if those systems stop working you die.

From that point on increasing exercise does indeed increase the body's calorific consumption.  Short term, long term, whatever.  Up to a 'hard limit', sustainable in the long term, of approximately 2.5x BMR on account of that being the maximum rate at which the body can ingest calories.  And there it will remain, indefinitely, while the work rate continues.

For a year in Gary McKee's case, running a marathon on each of his 5000 calorie days.  For their entire working lives in the case of Victorian navvies, a bit under 200 years ago, digging canals by hand and shifting up to 20 tons of earth each day with a shovel - also consuming about 5000 calories a day.  (According to various historical sources - I've posted enough links, google it yourself.)

It was that bit about "2.5 x BMR *indefinitely*" I didn't get. From the book, I thought he was saying that was not feasible. Genuinely,  thanks for clarifying.

Quick question from someone with no knowledge on this: is the implication of the research that to change body composition (‘lose weight’ - body fat) is pretty much wholly down to diet then?

Yes. There's good reasons to exercise, but long term, you'll never out train a bad diet. What constitutes a bad diet is where there's debate...

Looking at the study based around the Race Across the USA event in 2015, in which Pontzer was involved. The of the six participants that they looked at all but one lost weight, in one case a significant amount of weight (10%), but perhaps more importantly all saw improvement in body composition, i.e. significant reductions in body fat. It is worth mentioning that all of the participants would be within healthy weight ranges and were not doing the event to lose weight and were working hard to balance calorific intake with energy expenditure.

In much the same way as "you'll never out-diet a bad (sedentary) lifestyle". Life is never that simple and any sound-bite like either of the above really carry zero meaningful information.

Here's my totally unqualified* 2p on that:

I don't think it's even that - it's that attempting to lose weight wholly through exercise is probably futile.  There's a difference, and it would be a huge unjustified leap to go from that to "there's no point exercising".  (And can you effectively, and permanently, lose weight without exercising?  This study says nothing at all about that.)

So, the gist of the Hadza thing seems to be that if you make no other change to your lifestyle other than to move from being completely sedentary to exercising regularly - up to I guess about a maximum of about a 12km run every day (more or less what the most active hunter-gatherers in the study were doing), that won't burn any extra calories.

That's what that pithy phrase "you can't outrun a bad diet" is getting at - but in so far as that's true, it's only true purely in terms of weight loss.  You probably can outrun some of the consequences of a bad diet - whether exercise is good for weight loss or not, there is no doubt whatsoever that it's good for health gain.  Physical and mental.  On the physical side, the risk of heart disease and stroke for example.

And as far as changing your diet is concerned, health gain can only help to make that easier - mental health especially perhaps.  Less anxiety, less depression, more focus, better self-esteem..

Also, body composition isn't just about fat.  There's only one way to increase lean muscle mass.  And there's bone density too - for women especially, anything you can do to boost that is going to be well worth it as you start getting on a bit.

* (Ha ha.  I'm so, so, unqualified to be making that little speech.  But I seem to have given myself a bit of a pep talk there, so that's plenty of time staring at a screen for now - I'm off out for a run!)

I’ve been reading the book and was discussing it this morning with my wife as we walked to the train station.

We were talking about homeostasis and energy conservation more generally and I thought of something that I hadn’t thought of previously. We accepted that a degree of energy conservation occurs in relation to exercise, but to what extent does it occur in relation to calorific restriction?

To some extent I'm sure, and no doubt there's a ton of research and lots of books on the subject out there.  (A lot of it mutually contradictory I'm sure.)  In evolutionary terms a stock of body fat is a valuable asset that could be needed for survival at any time, so it's hardly surprising that our bodies might not be willing to give that up so easily.

But I'm not the guy to be getting involved in a "diet" thread on UKC.  Even I have better things to do with my time than that!