This blog is about the intersection between evolutionary biology and food. But also about practical applications, sustainable agriculture, and general tasty things.
I've noticed a few people tweeting this new paper, titled Hunter-Gatherer Energetics and Human Obesity, but I haven't seen many blog posts about it. Some of the tweets are to the effect of "haha, total proof that eat less, move more is a farce."
The paper is open-access, but the researchers published an editorial in the New York Times
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.
Unfortunately, the applicability to the average dieter in the United States might be limited. Notice "typical adults in Europe and the United States." I don't know, but last time I was in Europe, it seemed like people biked and walked places a lot more than in the US. As a non-driver, when I lived in Europe I was hardly the oddity I am here. In many places in the United States it is not even possible to walk to the grocery store. One study showed that the average American takes 5,117 steps a day, whereas the average Swiss person takes 9,650 steps a day. That's another issue with the Kitavan study, in that it also compares activity levels with a non-US group of people, the Swedish.
There is also the possibility that the Hadza are not expending as much energy as expected because of nutritional stress. Whether or not certain hunter-gatherer groups are naturally small or if they are exhibiting stunting is an important question. A paper that came out last year about a similar group of hunter-gatherers, the !Kung, re-opened this debate, speculating that the !Kung are somewhat malnourished:
Given the adverse conditions of life in the Mexican refugee camp, and the similar pattern of growth of the Maya and !Kung, the most reasonable interpretation of the growth of the !Kung infants and children is that it is due to inadequate food intake, disease, or a combination of both. Small size of !Kung infants and children sets the pattern of growth for older ages, as !Kung adults remain relatively short and light throughout their lives...
People with energy deficiency, or living at a delicate energy balance, do practice an economy of effort. Some examples are studies by George B. Spurr and colleagues of marginally undernourished boys and girls, ages 6–16 years old, in the city of Cali, Colombia. These boys and girls adjust their energy expenditure according to energy intake. In one quasi-experiment (Spurr & Reina 1988), normal and undernourished boys were observed at a summer day camp. They were encouraged to increase their physical activity by playing sports and other games. The undernourished boys were not able to keep up with the normally nourished boys during the morning session. At mid-day both groups received a meal and the undernourished boys received an extra 760 kcal of food, all of which was consumed. During the afternoon play session the undernourished boys were able to keep up with the normal group for about 2 hours, which is about the time they expended the extra 760 kcal eaten at lunch.
I would like to see similar data for the Hadza. And other foraging cultures, especially those with access to higher quality game. And it's worth remembering that even if the Khosian hunter-gatherer lifestyle is of continuous antiquity, it is the tip of the iceberg in terms of foraging. There were many very diverse paleolithic foraging cultures and so few of them are represented in the tiny remnants of this lifestyle available to study today.
Some books about the paleo diet reference the impressive height of paleolithic hunter-gatherers, comparing them to stunted agriculturalists. However, the archeological record is full of shorter hunter-gatherers and almost all modern foragers would be considered tiny. The average Hadza man is only 161.3 cm tall (5.3 feet). Is this stunting or is it genetic? Either way, some see their height as a feature, not a bug, contending that shorter people have certain metabolic advantages that are protective against many diseases of civilization. Hilariously, that paper I just linked to is posted along with many others on the website Short Support, which is all about how awesome short people are. At five feet two inches tall, I approve of this site.
Furthermore, it would be interesting to explore the genetic uniqueness of the Hadza. Another recent study showed evidence for genetic adaptations to local environmental conditions. The authors of this paper note that more research in this area is needed:
And indeed, studies reporting differences in metabolic-hormone profiles between traditional and Western populations support this idea (though more work is needed).
Also it's worth noting that physical activity has many known benefits beyond just burning calories.
Furthermore, it is quite funny to see how popular this study is with people promoting a low-carb diet because one of the reasons some of them have said foraging people can tolerate starch/sugar is because of their high activity levels. Though conveniently Rosedale has recently switched to saying it's because they are short, just in time for this study. Because honestly, the Hadza diet has quite a bit of sugar in the form of honey, berries, and baobab:
Dr. Lustig should come and tell them not to eat so much sugar. That humans aren't evolved to eat so much sugar and didn't have access to it in our natural evolutionary environment. Especially the honey. It's really appalling how sugary that stuff is.
Don't get me wrong, this is an interesting paper, but grouping Europeans together and then those Europeans with the particularly sedentary Americans means we can't use this paper to say that food is the main thing that matters in determining weight.
I'm sure you have your own take on this, since the paper is open access, I recommend reading it.