Eat smarter, don't work out harder?

By Razib Khan | August 26, 2012 5:53 pm

There have been several recent studies reemphasizing diet over exercise (timely because Americans are kind of fat, on average). A new piece in The New York Times looking at the Hadza of Tanzania, who are hunter-gatherers, seems to reiterate this point, Debunking the Hunter-Gatherer Workout:

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. And indeed, studies reporting differences in metabolic-hormone profiles between traditional and Western populations support this idea (though more work is needed).

As noted in the paper the researchers used urine samples to ascertain caloric expenditure. I’ve seen this in surveys of overweight people. One result was that many overweight people inadvertently under report their consumption (e.g., not writing down snacks that they ate) by as much as 1/3, so this is an essential check on self-reports. A reader brings up this relevant point:

They hypothesize that the Hadza save energy on unspecified activities other than walking and carrying loads. (Presumably digestion also is taking more energy for them?). Should we hypothesize that they spend less energy thinking? Any other good venues for energy efficiency?

BTW the paper starts out from stating that we “evolve as hunters and gatherers”, and IMVHO this statement requires a lot of qualifiers. For too much evolution happened after switch to agriculture to leave it unqualified, what do you think?

Here the reader is alluding to the fact that our brain utilizes ~25 percent of our caloric intake. In terms of energy it’s incredibly “expensive.” This is why it’s ridiculous to wonder if the human brain is a spandrel of some sort. Domesticated animals tend to have smaller brains than their wild ancestors, probably because they’ve offloaded some of the more cognitively intensive tasks to humans.

As for the issue with EEA, I think that’s a valid point. I checked over their references, and the authors don’t note the rather numerous studies since the mid-2000s which indicate that metabolism has been one of the major targets for natural selection in the Holocene (last 10,000 years). For example, Adaptations to Climate-Mediated Selective Pressures in Humans, or, Adaptations to climate in candidate genes for common metabolic disorders. If I had to bet I think the authors of the PLoS ONE paper are on to something, but they need to be careful to generalize from the Hadza, Western populations. In fact, I would be very curious to see a similar survey of the Bushmen of South Africa, and the Pygmies of the Congo. Probably the results would be the same, but it would still be informative to check to see if in fact these deeply diverged human lineages tended toward the same metabolic housekeeping and accounting. If so, then that might be the ancestral state.

By the way, I’ve been recording my own weight sporadically since the summer of 2010. I publish it on Facebook now and then, so I thought readers would be interested. I recommend this sort of thing to everyone, before more advanced self-quantification tools come online:

CATEGORIZED UNDER: Anthroplogy, Human Evolution
MORE ABOUT: Human Evolution

Comments (14)

  1. ryan

    I wasn’t as certain as the authors that the lesson of this study was diet, not exercise. Another way of looking at their results would be that exercise makes Hadza bodies handle the energy they consume in a different way than the sedentary western populations.

    As an aside, I think I’ve gained about the same amount of pregnancy weight as you have. My daughter was born in January. Is the implication that we’re spending acting like smiling, doting imbeciles that our bodies are storing as fat the energy our brains are no longer using.

  2. #1, 2/3 of the weigh gain was before my daughter. i more strenuous “day job” obligations, and started to eat at odd hours, and regularly sleeping 2-3 hours a night for days at a stretch. i started dropping pounds when i started to cut back on the bad impulse eating habits i’d developed from back then….

  3. ryan

    As I read about the doubly labeled water method, I become somewhat skeptical of this study. I can hope that researchers have found a way to compensate for differential rates of sweating, and the possibility that more of the body’s CO2 processing would occur at exactly the time the body was losing most fluid to sweat, while rates would tend to equilibrate in the water kept in the kidneys. Seeing no mention of such a methodology, I fear that what they may have discovered is not “similarity in metabolic rates across a broad range of cultures” but similarity in the composition of urine across a broad range of cultures.

    This seems to have been a technique used for decades in small mammals that don’t sweat. But admittedly there are 30 years of human tests, so maybe it’s been sorted out.

    I hope someone will tell me I’m wrong.

  4. spindritf

    Diet is obviously more important but a good workout doesn’t just burn calories, it also builds muscles (which in turn increase resting metabolic rate but also make you keep your shape even with some additional pounds) and lets you stay fit, or at least lets you know that you’re not. So yeah, work out harder. Actually, maybe deliberately lift some weights instead of talking that walk.

  5. My comment from G+ on this op-ed:

    Jochen: I don’t understand how someone can 1) do research laying out how energy use is massively manipulable by the body, 2) exercise affects profoundly all sorts of internal variables like hormones, and then 3) conclude that we should 3.1) not bother with exercise because it’s useless and 3.2) *eat less*.

    This isn’t just questionable. This is outright ignoring *both* of the major points of everything he wrote previously! If we really did #3.2, why would we expect it to succeed per #1? And why would we do #3.1 when #2 proves that #3 is wrong with its justifying claim?

  6. Jason Malloy

    Should we hypothesize that they spend less energy thinking?

    A recent article in Scientific American suggested that there is a basal level of energy consumed by the brain, and that problem-solving and sustained kinds of thinking don’t increase energy expenditure.

  7. Dekka

    An aside: Many years ago I was part of a fourth year psychology class that looked for evidence that smaller brains meant smaller intelligence. There wasn’t really a lot out there. There was a nice case study that showed a brilliant engineering student had no cortex at all. That was a while ago but I would say assuming that smaller brains means less thought is just an assumption. Unless you’ve got some evidence otherwise?

  8. Mitch

    It seems strange to look at a comparison between westerners and hunter gatherers and conclude that westerners shouldn’t bother with exercise because of how hunter gatherers’ metabolisms work.

    A better comparison would be between westerners who do nearly no exercise, and westerners who regularly exercise.

    And I suspect the results would shock no one in indicating that westerners who exercise are slimmer and healthier than those who don’t. Exercise has even recently been linked with cognitive function. “Getting the blood flowing,” and all that.

  9. vernon

    I’ve been on the “Paleo Diet” for a while now and one of the first things I learned, and it is a hallmark of this lifestyle, is that diet not exercise is responsible for my body becoming leaner and more muscular. It seems my fit body comes 80% from my diet and 20% from exercise. I work out, but only when I want to (not on a regular regimen) and it’s fun not serious exercise. I started the diet because I heard I could reverse my Graves Disease, and sure enough, 4 months ago my endocrinologist took me off my meds. He was amazed and confused but happy for me. The weight loss and toning were just an added bonus.

  10. Karl Zimmerman

    From what I have read about the level of physical activity actually undertaken in hunter-gatherer societies, I wouldn’t have made an assumption it was particularly strenuous.

    Although the original estimates from the 60s of the small amount of time hunter-gatherers spend on survival were too low, they still seem to spend far less time acquiring and preparing food (about six hours a day) than humans in the modern west do when work and household chores are combined. About half of this time is spent on food processing and cooking, which (excepting opening up nuts and the like) is mostly not strenuous work. Much of the remainder of the time is mostly spent walking around carrying loads no heavier than a typical backpack – even endurance hunting involves fast walking paces more than actual running. The bottom line is I don’t think that the average hunter-gatherer exerts themselves much more than many New Yorkers (or residents of any city with little car use) do in a typical day.

    Agriculturalists are another matter – it’s obviously horribly strenuous work with very long hours, and I’ve read many farmers need 2.5-5 times as many calories as those with modern sedentary western lifestyles. It’s no wonder that it’s thought that essentially famine was what caused agriculture to be adopted – I don’t see why anyone would willingly shift from being a hunter-gatherer to a farmer, unless they lucked out and got to be a chieftain.

  11. Kiwiguy

    # 7,

    See Paul Thompson & Jeremy Gray’s paper on the Neurobiology of Intelligence.

    # 9,

    I’ve found that too from reading about intermittent fasting programs such as Leangains and Eat Stop Eat. A number of paleo sites refer to research on hunter gatherers getting the bulk of their daily calories in the late afternoon or evening.

    My GP had suggested I was borderline obese according to BMI (230 lb, 6ft) and recommended exercise. I started intermittent fasting (16 hours from dinner to next meal) on 23 May & dropped from 230 lb to 210 lb by July – no exercise.

  12. Sandgroper

    #11 – Question – how much of the loss in mass was fat, and how much was loss of muscle mass?

    #9 – “It seems my fit body comes 80% from my diet and 20% from exercise.” Unless you have been doing accurate measurements of body fat %, you don’t know that. It could just be that loss of subcutaneous fat has resulted in the muscles being more defined, which makes you think you are more muscular, when in reality you might not have gained in muscle mass at all, and might even have lost some – depending on just how much of this ‘fun’ exercise you do, and what sort of exercise it is. Weight training a couple times or even only once/week will maintain or even increase muscle mass. Aerobic exercise won’t, much.

    I exercise every single day – I still think of it as fun and look forward to it. The truth is I’m probably addicted to it – it’s about the best addiction you can cultivate.

  13. Sandgroper

    I regard this paper as a joke, BTW. #8 is on the money.

    Hunter gatherers typically don’t have a lot of muscle mass – they’re not very muscular compared with say modern strength athletes and sprinters.

    If you want to be skeletal, stop eating. If you want to lose fat while maintaining or increasing muscle mass, you need to exercise as well, and it needs to be a balanced program of aerobic and non-aerobic exercise.

    I once lost 35 lbs in 6 months. My waist measurement went from 37″ to 31″. (I’m 5’10”.) All I did was (1) I cut out anything with added sugar, and anything with alcohol in it – aside from that, I stuffed myself, including with heaps of white rice. (2) I swam a mile of freestyle every day – apart from that I was pretty sedentary. At the end of 6 months I was almost skeletal – my body fat was low, but I also didn’t have much muscle mass. I was ‘fit’ in cardio-vascular terms, but I looked lousy – the lesson I learned from that was I needed to incorporate weight training, and be slightly less fanatical about sugar intake – but only slightly – sugar in any kind of quantity is bad stuff. No one actually needs alcohol, though – that’s something you can cut out without losing anything positive at all. I guess one glass of wine now and again won’t hurt, but do you actually know anyone who does that – has one glass of wine now and again, and stops at one?

  14. otti

    in the way they present the study, they act like each person is essentially the same, and only the activity level between the two locations is the single factor that causes a different metabolism level in US residents vs. Hazda.

    However, what about the variability in response to exercise and calories within a population? If there can be this dramatic of a response to increased exercise, why wouldn’t we first suspect that fat people in the U.S. have metabolisms which overrespond to food availability? Why would we imagine that they would lose weight easily if they cut back calories, particularly when many fat people report that they diet and diet and don’t get any results.


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About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at


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