The Hadza Hunter Gatherer Energy Expenditure Study
I've been asked by a few people to weigh in on a recent NYT article, Debunking the Hunter-Gatherer Workout, that discusses the following study (free full text): Hunter-Gatherer Energetics and Human Obesity. I didn't have a whole lot to say until I wrote this, and now it's rather long ... so I guess I did have quite a bit to say after all ;-) But first, a little link love for Colby Vorland of nutsci.org who discussed this back in July: Westerner energy expenditure compared to a hunter-gatherer population is equivalent. In addition, Colby had discussed Energy expenditure and physical activity level are not higher in developing countries compared to industrialized. I encourage reading both.
So from the NYT article:
We found that despite all this physical activity, the number of calories that the Hadza burned per day was indistinguishable from that of typical adults in Europe and the United States. We ran a number of statistical tests, accounting for body mass, lean body mass, age, sex and fat mass, and still found no difference in daily energy expenditure between the Hadza and their Western counterparts.
How can the Hadza be more active than we are without burning more calories? It’s not that their bodies are more efficient, allowing them to do more with less: separate measurements showed that the Hadza burn just as many calories while walking or resting as Westerners do.
We think that the Hadzas’ bodies have adjusted to the higher activity levels required for hunting and gathering by spending less energy elsewhere. Even for very active people, physical activity accounts for only a small portion of daily energy expenditure; most energy is spent behind the scenes on the myriad unseen tasks that keep our cells humming and our support systems working. If the Hadza’s bodies somehow manage to spend less energy in those areas, they could easily accommodate the elevated energy demands of hunting and gathering.
In comments on this blog, it has been mentioned that the study did not report caloric intake ... and I think it may well come down to this. I am not seeing where they measured body composition -- fat free mass, FFM -- rather it was calculated by linear regression of the doubly labeled water test (??). I would have a bit more trust in the analyses that correct for FFM if body composition were determined by DEXA or some direct means. When comparing to other populations, BMR and FFM data were often not available for those populations and were estimated.
Not sure what this tells us really. I find the journal article to be rather confusing. In a Time article on the same study they state:
This counterintuitive finding is explained by the foragers' lower basal metabolic rate: they expend less energy while at rest, even when we compare people of the same size and age.The article seems to say that controlling for every factor energy expenditure is the same. And yet I don't see how this can be the case when there are some things that differ so dramatically.
The Hadza men vs. Western men are on average 11 years younger (33 v. 44), 30 kg/66 lbs lighter (51 v. 81 kg) -- they are over 20 kg/44 lbs lighter than Western women!!, 9% less body fat percentage (13.5 v. 22.5), by my calculations over 20 kg less FFM (44 v. 63). So let's do some more calculations, shall we? Using group means, Hadza v. Western men:
TEE cal/day: 2649 v. 3053 (87%)Using PAL = TEE/BMR calculated the BMR = TEE/PAL
TEE cal/day-kg BW: 52 v. 38 (137%)
TEE cal/day-kg FFM: 60 v. 49 (122%)
BMR cal/day: 1172 v. 1687 (70%) BMR cal/day-kg BW: 23 v. 21 (111%) BMR cal/day-kg FFM: 27 v. 27 (100%) ← per kg FFM, equal BMROh wait ...
We also measured daily walking distances (km/day) using wearable GPS devices, and the cost of walking (kCal kg−1 m−1) and resting metabolic rate (RMR, kCal kg−1 s−1) using a portable respirometry system (Text S1). Because it was not feasible to measure basal metabolic rate (BMR, kCal/day), we calculated physical activity level (PAL) as TEE/estimated BMR (Methods).So those BMR's were estimated from a table rather than using the RMR data (reported at all?) which was on average 11% higher than the estimate. But presumably this was done for both populations.
Lastly, they seemed somewhat surprised to find that the Hadza expended equal energy for the act of walking as Westerners. For the Hadza, walking was approximately 11% of their TEE -- well, that equates to just under 300 calories/day. This is for an average of 11.4 km = 7.1 miles per day. From the supplemental data (S1), the cost of walking for Hadza was similar to others, though a bit more variable, at approximately 0.5 cal/kg/km. This does calculate out to the just under 300 cal/day for 11.4 km, but really doesn't jibe with what I've always been told -- that walking a mile burns roughly 100 cal, so the male Hadza should be expending over 2X the estimates made by these researchers using their methods. Perhaps this is because:
Walking cost was measured in 14 subjects (5 women, 9 men) during over ground walking on a level trackway established near each camp on flat ground (Text S1). The minimum net cost of transport, COTmin (kCal kg−1 m−1), which for all but one subject occurred at the slowest walking speed, was averaged across subjects. Mean COTminfor the Hadza sample was compared to sample means measured in Western populations presented in a recent meta-analysis of walking cost .
From this study: Twenty-four young adult male subjects were used to study the relationship between total caloric costs (exercise and recovery costs) incurred and speed of movement over a distance of 1 mile. Caloric costs were determined at walking speeds of 3, 4, and 5 mph and at running speeds of 5, 7, and 9 mph. Energy costs were assessed every 20 sec during the activity and during the recovery until the caloric cost returned to pre-established resting levels. ... Conclusions for the given speeds were: (1) running is more costly than walking, (2) the cost of walking a mile increases with speed of movement ...The caloric cost of walking is understated by comparing minimum costs with actual costs. Also, these hunters and gatherers are often toting things (bow & arrows, kill for the men) which would be the equivalent of weighted walking. In this study:
The energy cost and intensity of exercise performed at 0% grade were determined for walking at 2, 3, and 4 mph, running at 5, 6, and 7 mph, and walking at 2, 3, and 4 mph with ankle and/or hand weights. Subjects were young moderately trained males (4) and females (3). The energy cost per kilogram of body weight was similar between sexes, and data were combined for among-treatment comparisons. Intensity of effort and energy cost per minute and per mile were increased when weight was added during walking ... Gross energy cost per mile during weighted walking (120–158 kcal/mile) was comparable to and in some cases exceeded that of running which was independent of speed (120–130 kcal/mile). During nonweighted walking, the energy cost (kcal/mile) was significantly greater at 4 mph compared with 2 and 3 mph which did not differ. ...Whatever the case, and judging from the mass-media articles and the discussion in the paper itself, this study appears to be a Gary Taubes dream come true. Until you look more closely. Here's what the study really tells us:
- Western men weigh almost 60% more than their Hadza counterparts
- Western men have 45% greater lean mass than their Hadza counterparts
- Western men burn almost 45% more calories just sitting on their butts (BMR) because they are bigger -- a lot bigger -- than the Hadza.
- A better comparison then is Non-Resting EE which for the Hadza is 1477 cal/day vs. 1396/day for Western men. Well now that's similar ... but ...
- NREE per kg BW is 29 cal/day for Hadza vs. only 17 cal/day for Westerners ... and ...
- NREE per kg FFM is 34 cal/day for Hadza vs. only 22 cal/day for Westerners
To me here are the take home messages:
- The Hadza most definitely have per kg (whether total BW or FFM) have higher energy expenditures due to their activity level.
- Western total energy expenditures are higher because we are bigger -- and fatter!
In the end, I think it's somewhat meaningless to compare the two. Why? Because the Hadza intake and expenditure are inextricably linked because they expend energy to obtain energy -- humans in the wild! On some level, conscious or otherwise, these people must weigh the benefits of obtaining more food with the effort they must expend to do so. Therefore they don't hunt/forage to excess and they are in energy homeostasis. There is no analogous situation in Western life, even back in the 60's before this obesity epidemic took off or in Little House on the Prairie days (that folks on Jimmy's forum used to love to bring up). I think the more instructive considerations vis a vis the impact of activity on body weight to consider:
- What do you think would happen if you took a Western man and sent him to live among the Hadza for 6 months?
- What do you think would happen if you took a Western man and sent him just to mimic the lifestyle of the Hadza for 6 months but gave him the same amount of Western food he was accustomed to eating?
- What do you think would happen to a Hadza if he didn't have to hunt his food and instead had unlimited access to traditional Hadza foods in a supermarket?
- What do you think would happen to a Hadza if he was transplanted to America?
I'd say that in cases 1 and 2 you'd see improvements in Western man, moreso in 1 than 2, because in case 1 he'd be eating less and moving more, where he would just be moving more in case 2. Hadza man would see his health deteriorate more than the improvements in cases 1&2, and here's why: he has a lower total BMR. I think he'd stand a fighting chance in hell of his health not deteriorating too much with traditional Hadza foods, but currently, 56% of the TEE of the Hadza NREE, almost the opposite of your typical Westerner where REE(BMR) makes up 60% of TEE (and closer to 75% for the very sedentary). It's fair to say that if he didn't need to expend energy to obtain food, he wouldn't be out doing it just for the recreation of it all! Give him free access to calorically dense refined junk foods and he's toast.
Here's where comparing our culture and changes in it over the past 40 or so years with modern hunter gatherers in hopes of comparing ourselves to our long long ago paleolithic ancestors looking for answers seems rather misguided to me. I used to argue this all the time after I read GCBC, all of the various supposed paradoxes Taubes lists where obesity and poverty and/or malnutrition exist concurrently, can be explained by good old fashioned energy balance. If one is raised in an environment of scarcity, their metabolisms adapt to be slower and more efficient to do the basics. Give that person more plentiful food later in life and they will tend toward obesity. If you think energy expenditure and activity have nothing to do with it, look at what happens to retiring athletes who do not make an effort to either take up another activity and/or deliberately curtail their eating? They get fat.
Studies like this just miss that Occam's Razor thing: Anyone in my generation (Naughton even highlights this in the beginning of FatHead) who does not believe Americans are more sedentary as a population than in the 70's is kidding themselves. And anyone in this audience that doesn't acknowledge that by any means or source of the information, we are eating more -- to the tune of 300-600 cal/day as a population depending on the source -- is also kidding themselves.
I have an idea: The Hadza diet. At least walk to and from the supermarket daily for your food and prepare it standing up. Highly impractical for most of us, but it would be a start.