Book Review - Herman Pontzer's *Burn*
On human metabolisms and maximal weight loss pessimism
Are you interested in human metabolism? Why chimps don’t get fat in zoos? Why the power output of Tour de France competitors seems bounded at a pretty visible asymptote? And of course, the perennial standbys - weight loss or being fit? Herman Pontzer’s Burn might be for you.
I’ve been on a bit of an “intellectual descendants” tear lately - Pontzer started in Daniel Lieberman’s lab, whose Exercised I recently read, and heartily recommend. Reading Pontzer was a natural outgrowth of that.
Pontzer’s thesis and primary research result is that your body compensates for increased physical output over time, nerfing most exercise efforts by 2/3 in terms of excess caloric expenditure (ie if you exercise 360 cal extra a day, your body will eventually get that down to only needing 120 cal incremental daily in food). Worse, in the limit, your body will nerf your incremental efforts 100%, which is determined by looking at 5x active Hadza hunter gatherers vs sedentary moderns, and measuring that both (unexpectedly) have the same Fat Free Mass daily caloric expenditure.
This is good in one sense - that delta for non-exercisers is used to reduce inflammation and depression and anxiety and heart disease and all the other “diseases of civilization,” and that incremental “lost” 240-360 is directly eating into your ‘diseases of civilization budget’ and preventing them and keeping you healthy. Diseases of Civilization, so called, because hunter gatherers don’t get them. This includes a number of more-or-less surprising things, like Alzheimers, diabetes, metabolic syndrome, diaper rash, and much else1.
This is bad, because it represents the latest science, and is the maximally darkest, abandon all hope ye fools, weight-loss-pessimistic scenario. It means for regular people, exercise will not help you lose weight, and that rigorous calorie counting is the One True Way™ with all else folly and waste, with exercise then required *additionally* to keep it off. So, hard mode. But we already knew weight loss was hard mode if you’ve paid attention to any of the long term meta analyses (98% failure rates at keeping it off 5 years later).
There’s this great quote from an anonymous obesity researcher along the lines of “well, we’re screwed if exercise only cuts your all cause mortality to 1/4 of sedentary people, only vanity is a strong enough motivation to get people to exercise” in the book regarding this. I mean, I think that’s basically true.
Like, *obviously* it’s possible to lose weight and gain muscle and look good - go to the gym and there’ll be 20 meatheads demonstrating it, and most of them have never read a single book on this, much less pored over peer-reviewed study results. So getting upset that “exercise in tiny amounts is pointless and won’t really help you lose weight” is mistaken.
Also obviously, you can work out in more than “tiny amounts.” I routinely burn 1k+ calories in a single 60-90 minute workout in the gym, and that’s measured by my Polar H10 heart rate monitor and by my weight if I’m not on top of my calories, not by aspirationally-minded gym machines.
So really it just means the bar has been raised, and that “tiny” doesn’t cut it. So if you’re serious, you’ll count calories and macros rigorously, AND put in real workouts. And that’s the road to accomplish what all the meatheads have already accomplished. Nobody said being top 2% or better was going to be easy, but empirically we already kinda suspected that was the bar, because 98% of dieters fail to keep the weight off long term.
And of course, now we have a magical pill / injection to solve obesity - the first pass for everybody interested in losing weight should probably be the ‘tides now.2
There are still absolutely massive positive benefits to exercising - you get to quarter your all cause mortality if you do enough, you get to avoid or greatly ameliorate those diseases of civilization, you feel better, you’re stronger and more capable in your daily life - but basically everyone knows these things (or things directionally shaped like them), and doesn’t exercise. If you really want to be convinced to do it, read Lieberman’s Exercised (or my review).
In the book, Pontzer also brings up several factoids that point in interesting and fun directions for solving the obesity crisis. First, other apes don’t get fat. Humans are unique on this front. Chimps, Orangutans, and Gorillas in zoos are 20-50% bigger than their wild counterparts - the surplus goes to fat free mass and bigger organs, and zoo chimps still cruise around 10% body fat.
I’m sure you remember, we share 98% of our genome with chimps. Hellloooo chimp splice! Seriously, of the many space-race-level funding CRISPR programs we should be aggressively pursuing for the public good,3 this should be added pretty high on the list.
Another fun factoid - it takes only 700 calories to launch a 200 pound man 2 miles up into the air. And did you know fat is roughly as energetically dense as jet fuel? It would take about 3 ounces of fat to expend those calories. Why aren’t we gengineering our fat people to be explosive strength athletes who can powerclean a couple of tons?? Why can’t we / they go around uppercutting MF-ers *2 miles up* for the low low cost of 3 oz of fat???
Tell me that ability wouldn’t solve the obesity crisis basically overnight! Well, to all the bioengineering nerds out there, there’s the idea, it’s a simple matter of rate throughput and engineering at this point! (You know, just like hyperloops are simple matters of getting maglev in a vacuum right, two well understood concepts, what’s the hold up??😂😂)
Finally, the results as they pertain to endurance athletics and / or training - what I’m here for! And here, I came out with more questions than answers, and a number of research frontiers to look into.
If you want a broader overview of endurance training and the key factors to performance, pop over to my review of Alex Hutchinson’s Endure.
The main takeaway, metabolism wise, is that he posits a 2.5x BMR hard cap on persistent energetic output, with pregnancy running 80k calories incremental at that threshold for 9 months, and being the sort of “length x effort” flagship thing humans routinely do. He has some pretty interesting graphs of expenditure vs duration.4
Question 1: But since the only independent term in the BMR equation is your weight, why aren’t all the endurance things dominated by huge people?
Obviously, it’s multifactorial - heat loss being important and volume * surface area disfavoring larger people, per-kg efficiency, scaling, etc. But still, at the *least* you’d expect to strongly favor bigger people and people with naturally higher BMR’s.
He also posits that there’s a hard calorie cap per day of ~5k calories5, and the long endurance events like TdF (8.5k daily) and Race Across America (2.6k plus BMR) are literally fueled by weight loss, and this weight loss defines the frontier of peak human capability over time.
More questions: But again, why wouldn’t this be dominated by larger people, or people coming in with muscles but also a noticeable layer of fat over all the muscle to be able to fuel the endeavor from reserves? Is there some digestive efficiency tradeoff? Is it a scaling law thing? Because the scaling law for animal size would argue large people would be MORE metabolically efficient.6
Also, with the 5k daily calorie limit, why isn’t this addressed by better, more digestible food? I assume it already means “at the limits of current athletic knowledge on refueling,” ie energy gels and pure carb and fat solutions or whatever. He mentions IV fat and sugar used in TdF in the 80’s, which slowed weight loss. Why only slowed? What’s the max absorption rate for IV calories per hour? How do chimp, pig, and dog digestive efficiencies differ vs human? How do you breed or gengineer for digestive efficiency? Why don’t athletes take supplemental digestive enzymes like Creon to juice this?
There seems like a totally unexplored athletic optimization frontier here as phrased, but I’m sure historically the various Olympians, ultra endurance athletes, and TdF-ers have considered basic ideas like “eat more” or “eat more efficiently,” so I’m not really sure why this space hasn’t been fully explored, or if so, why gaming it more isn’t possible.
And what about Michael Phelps, of “12k calories a day” fame?? To Pontzer’s credit, he says he gets this question all the time. He calls out Phelps as being bigger than average (so higher BMR from size), additionally he probably has a BMR variant on the higher end of his range, with likely better digestive efficiency than most, allowing him to credibly eat 7k a day. Says the 12k figure is puffery and marketing, voiced by essentially a PR guy on his team taking a wild post-hoc estimate. I’ve looked into Olympic calories by sport while training, and his 5-7k cap seems plausible on it’s face. Plus, if we tackle it from the other direction 12k even with a 3k BMR would be 9k calories expended in exercise, which is something like swimming 24-48km a day, depending on pace, which sounds ambitious even for Phelps.7
He closes the book with a couple chapters about climate change and “inequity,” that I tuned out as being his personal hobby horses and nothing to do with the substance of the book (besides overall energy balance, ie us needing 8 Cals of energy from gasoline per food calorie generated).
But overall, was it interesting? Very much yes.
Did it give me some ideas on training frontiers to pursue? You bet.
Was it the maximally pessimal weight loss scenario, as supported by the latest science? It was that too. God (or at least Ozempic) help us all.
No marathons run against horses though, sadly - you have to read Lieberman’s Exercised (or at least my review) for that.
Now, one of my favorite parts - the book was absolutely packed with fun factoids, which I’m just going to list without much further commentary:
Human Metabolic budget:
20% muscle
20% liver
20% brain
20% heart and kidneys
20% everything else
As energy storage, Fat is 255 cal per ounce, more than 5x nitroglycerine, 100x an alkaline battery, roughly on par with jet fuel.
Calories are formidable: it only takes 700ish to launch a 200lb man / payload two MILES up into the air. Less than 3oz of fat. Why can’t we explosively liberate this energy, and literally uppercut mf-ers 2 miles up for the cost of a few ounces of fat?? Now THAT solves the obesity crisis in a fun way - let’s make literally explosive super athletes out of fat people.
Calorie cost per mile: walk 50, run 100, swim 300
Difficult chess grandmaster matches and memory tasks only burn an incremental 4 cal per hour - so much for “mental effort” counting for anything, food wise
In northeastern Jordan, they were baking bread from wild wheat 14.5kya
Inuit, the only living population to have no grains or carbs in their diet, have a mutation such that they don’t go into ketosis (FADS gene). Although Pontzer tries to argue that ketosis and keto diets don’t actually affect weight loss in the book, I think that this mutation achieving fixation in Inuit populations argues that ketosis as a mechanism for low carb benefit probably IS a more wasteful / metabolically burning mechanism, otherwise why is it so advantageous to avoid it?
240ml of ice water takes 9 cal to warm up. So, drinking a glass of cold water is going to burn twice as much as being a chess grandmaster in the middle of a match.
With his example of pregnancy as one of these “peak output” things, it also argues that the larger the woman, the more calories she can put into the child, which seems like a reasonable assumption. But if you want strength / size, why isn’t this common knowledge for athletic families / China breeding athletes? Also, the equation seems highly simplified, only considering weight in pounds vs height or FFM.
Animals get 40x payback per calorie, and HG 10x.
Horses can exert 640 cal of physical force per hour for 10 hours a day. This translates to 25-32k calories burned (due to muscle to work efficiency), and that’s before the horses BMR! If the 2.5 factor holds, that means work horses eat 35-45k cals per day!
My daily BMR (7 x 185 lbs + 551 is his equation) is prob 1800-1900. TDEE max is then 3600 at 2x and 4500 at 2.5x, which is about the calorie ceiling I’ve ever achieved while competing. So 1800 - 2500ish “expenditure” headroom.
900 gene variants associated with obesity, nearly all of them focused on the brain.
He posits the obesity crisis as being driven purely by variety and processed foods, gives famous KD Hall rats and prisoners study examples (rats / humans with western food with cafeteria style choice all get fat vs rat / prisoner chow)
Hadza acquire 1-1.5k cal per hour of foraging. Tsimane 1.5-2k. In 1900 USA, one median labor hour 3k cal, today 20k.
HG (hadza) vs forager-farmers (tsimane), 6 vs 9 kids - caloric efficiency and surplus is being directly converted to more descendants - it’s the entire agricultural revolution and takeover writ small.
Energy density of western diet 20% higher than Hadza - and from that 20%, an obesity epidimic is born in the margin!
Median American lifestyle consumes 210k cal a day with aircon and gasoline etc, about as much as 77 HG or a 9 ton elephant (even African elephants only 7 tons, not the best analogy). Globally, average is 47k a day per person.
In industrialized food supply chains, 8 cal is spent for every 1 food calorie produced.
Us cal budget: 500 trillion growing food, ten times that (5 quadrillion) heating and cooling, 7 trillion transportation.
Hadza do 5x the physical activity and eat 5x the fiber per day vs westerners.
Says Americans spend 87% in buildings and another 6% in cars, so 93% of time indoors, versus HG outside 66-100% of the time.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7584376/table/T2/?report=objectonly
Semaglutide, Liraglutide, Tirzepatide, Exenatide. A compounding pharmacy is the way to go, because it’s about 10x cheaper per month, and they don’t have supply shortages.
Do you know there’s an SNP that let’s people get 2-3 hours less sleep per night? That ALONE would drive hundreds of millions of life-hours and massively increased productivity, just in the US.
Then we should be doing general sleep less GWAS’s, massively parallel CRISPR programs for affecting hundreds to thousands of genes at a time for IQ, health, conscientiousness, etc
Of course in real life, we’re doing none of these, because we suck and no country in the world currently takes human gengineering seriously.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6551185/figure/F1/?report=objectonly
“C. Thurber et al. (2019). “Extreme events reveal an alimentary limit on sustained maximal human energy expenditure.” Science Advances 5 (6): eaaw0341. doi: 10.1126/sciadv.aaw0341.”
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6551185
See Geoffrey West’s Scale for a book length treatment here, but basically, larger animals are more metabolically efficient at a cellular level, ie if you look at elephants or whales, they expend less energy per cell and live longer than smaller animals like humans and mice, and this is a general scaling law dictated by optimal packing of blood vessels.
If you’re a swimmer, that’s 1-2k 25’s. PER DAY. EVERY DAY. At a 30s average pace, that’s 16.66 *nonstop* hours in the pool at the high end. You could get that down to ~4 hours a day at a 15s pace. But a THOUSAND 25’s at a 15s pace??? And remember, that’s with zero rest or breaks, which anyone actually trying this would need, bringing it back up to 6-8 hours in the water a day. Crazy even for Phelps.
Maybe humans evolved to be more efficient than the great apes in storing energy as fat. It seems that famine was a much bigger concern for us than our jungle relatives since we decided to move out of africa..maybe it sounds simplistic but that comes to mind. Great article anyway, cheers