Imagine this scene – a personal trainer barking at his flabby pen-pushing charges to push themselves through the pain barrier and climb those steps because “the human body wasn’t designed to sit at a computer all day”. It’s easy to imagine because of the common perception that the root cause of the current obesity epidemic is a radical shift in human behaviour – from the hunter-gatherer ways of our ancient ancestors to our current sedentary lifestyles with diets high in energy-dense and highly-processed foods.
But, in a paper just published in PLoS One researchers from the United States, Tanzania and England have shown that there’s actually no difference in the energy expenditure of the modern American in comparison to the closest modern comparator we have to the hunter-gatherer lifestyle, the Hadza foragers of Northern Tanzania.
According to the authors, although the hunter-gatherers do indeed walk far more than your average American, they actually expend the same amount of total energy. Based on these findings, the authors challenge the view that obesity in Western populations results from decreased energy expenditure, placing the blame squarely on our high-energy diets.
This is an intriguing finding but what are we to make of it when all the advice we receive (including an article on this very site not long ago) is to get moving to halt our expanding waistlines? Is all this advice based on insufficient evidence?
The best place to start answering this question is through a closer examination of the validity of this latest hypothesis.
The first assumption implicit in the research is that “globesity” is the result of a change in lifestyle from ancient hunter-gatherer to modern human behaviours of sloth and over-indulgence. But anyone from the generations that preceded X,Y and Z will tell you that when they were growing up, there was no such thing as an obesity epidemic.
In Australia, as in much of the world, it was really only in the 1980s that obesity started to become common. In fact, the roots of the obesity epidemic stretch back no further than the early twentieth century.
So although it’s interesting that energy expenditure is similar in the modern American and the hunter-gatherer from Tanzania, to get to the root cause of the obesity epidemic the question that really needs asking may be how is the lifestyle of Americans in 2012 is different to that of an American in 1920? And the modern love affair with computers, cars, labour-saving devices, video games and television will tell you the answer to that one.
But an even more important issue with this research is its sole focus on activity. By comparing the energy expenditure of a hunter-gatherer from Tanzania with a modern-day American, the researchers have lost touch with half of the obesity equation.
If I were living on the diet of a forager from Tanzania, I doubt I would feel much like going for a jog at lunchtime, going to the gym or riding my bike home from work. Energy intake (eating) matters too!
It seems amazing to me that on their limited diet, the hunter-gatherers still managed equal energy expenditure and far greater levels of physical activity than well-fed Americans. They exist on limited calories but maintain high levels of physical activity while the latter takes in copious calories and has little physical activity, despite similar levels of total energy expenditure.
It isn’t really surprising that the body fat of the Americans is twice as high. In reality, we still have a fairly limited conception of how human physiology works in response to different levels of activity. To compare the activity of two very different groups is a further challenge. And to not account for the gross discrepancy in energy intake between them makes that comparison even more fraught.
We would never assume that the enormous appetite of an Olympic athlete lead to high levels of body fat or is linked to low activity levels. Intake is a critical part of the energy balance equation and we would be unwise to write off the obesity prevention advice to stay active based on a study that doesn’t account for diet.
The soaring increase in average BMI (body mass index) over the last 30 years is a result of a multitude of factors, some of which may not yet even be apparent. The evidence we do have suggests that it’s not just physical activity or diet that matter in obesity – it’s both acting together.
Modern sedentary lives, while apparently requiring that people expend as much energy as hunter-gatherers, are not sufficiently active to combat the large portions or energy-rich, processed food that’s offered at every turn.
We have increasing evidence that sedentary behaviour is making us sick and even killing us, and to deny that would be to stick one’s head in the Tanzanian sand.
Andrew Partridge
self-employed
The US per-capita energy consumption being equal to the hunter-gatherers could be explained by the fact that a fat person expends more metabolic energy than a skinny person.
This phenomenon would actually act as negative feedback to reduce the amount of weight gained for a given amount of overeating. Unfortunately, there are also positive feedbacks as well; for example, the heavier you are the less exercise you are likely to take.
I suspect the energy consumed through activity by Americans is generally much less than for the hunter-gatherers - I can't imagine that waggling ones fingers over a keyboard comes close to the energy requirement of walking or running all day.
Seamus Gardiner
Citizen
This is a really fascinating topic and I found the conclusions counterintuitive, it's always good to have one's assumptions challenged and ideas changed. The original paper does make the point that, although Total Energy Expenditure is the same for both cohorts Physical Activity Level is much higher in the Tanzanian Hunter Gatherers, what explains this discrepancy?
Read moreThe Tanzanian cohort are smaller in body mass, which makes any movement against gravity less energy demanding than a heavier person…
Steve Brown
logged in via email @yahoo.com.au
I found this a very frustrating read, Mr Cameron!
You raised the (very important) evolutionary argument yet totally ignored the most important aspect of it- not the calories consumed or expended but the ACTUAL differences between the two diets!
Researchers appear to have become so obsessed with this (baseless*) theory about calories in-calories out that they have become myopic.
Did you not at all wonder that the seed oils, grains and other agricultural and industrial 'foods' which separate our societies from hunter-gatherer societies may have radical effects on the body, one of which is weight gain?
I'm thinking you didn't, which is a shame! There is a wealth of data showing the ill effects of these substances and it seems the mainstream are totally unaware of it.
*a 2010 study comparing a calorie restricted diet to low-carb calorie unrestricted diet resulted in exactly the same weight gain.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2949959/?tool=pubmed
Andrew Partridge
self-employed
Steve Brown,
I agree with your observations. The paper you referred to, "Weight and Metabolic Outcomes After 2 Years on a Low-Carbohydrate Versus Low-Fat Diet", notes that "attrition at 2 years was high", and I'm wondering if the reasons for this might be:
(1) Those on the low calorie/low fat diet were always hungry on the diet and so it was easy to slip back to old ways of eating;
(2) Those on the unlimited fat and protein but low carb diet would have gasped at the deterioration of their cardiovascular health at the end of the 2 years (noted in the paper) and attempted to change to a low fat diet.
I would like to have seen what happens when one group eats only fats that are naturally-occurring, minimally processed, and produced with regard for correct omega-3 ratio, e.g. fat from grass fed animals and unheated coconut oil, rather than polyunsaturated margarine and vegetable (really seed) oils.
Tom Hennessy
Retired
It's our high meat diet , due to refrigeration , plus iron fortified food .
"These results suggest protein carbonylation plays a major instigating role in cytokine-dependent mitochondrial dysfunction and may be linked to the development of insulin resistance in the adipocyte."
http://www.ncbi.nlm..gov/pubmed/22822087
Andrew Partridge
self-employed
Tom Hennessy,
Your link was broken, here is the correct link:
http://www.ncbi.nlm.nih.gov/pubmed/22822087
I might be wrong here (this paper is waaay over my head), but I don't think the paper is suggesting anything to do with diet (and if it is, I would be very wary of extrapolating this detailed biochemical study to dietary and other lifestyle changes), rather I think it is trying to explain the mechanism by which obesity causes various other health issues. So if there is a lifestyle message from the paper, it might be: "Don't be obese, whatever it takes to achieve that".
Tom Hennessy
Retired
You are correct it doesn't mention diet ,but it does mention oxidative stress / carbonylation
Tom Hennessy
Retired
The whole question is 'why' is everyone fat NOW , as opposed to before? The hypothesis is the high intake of iron leads to oxidation / oxidative stress / rust from this iron.
Refrigeration has allowed us to eat meat morning, noon and night , plus iron fortification of all our foods .
"Iron-mediated oxidation of LDL"
The increased oxidation , carbonylation , involved in the obesity causing syndrome , insulin resistance , is caused by this increased iron stores , as evidenced in women when they hit menopause and their iron stores rise their diabetes also rises .
Tom Hennessy
Retired
"These results provide evidence for linkage among body iron stores,
transaminase activity and the prevalence of cardiometabolic risk
factors in apparently healthy, non-obese adolescents even within the range of normal laboratory and anthropomorphic values and suggest that iron
stores should be investigated as a potentially modifiable risk factor in
healthy teenagers."
http://www.ncbi.nlm.nih.gov/pubmed/20050877
"The frequency of the metabolic syndrome increased with both serum
Read moretransferrin…
Tom Hennessy
Retired
"Risk Associated With Iron Supplements
Iron is a double-edged sword. If we don’t absorb enough, we risk anemia, but if absorb too much we may increase our risk of cancer, heart disease, and a number of inflammatory conditions. Because the human body has no mechanism to rid itself of excess iron, one should choose plant-based (non-heme) sources over which our body has some control"
http://nutritionfacts.org/video/risk-associated-with-iron-supplements/?utm_source=NutritionFacts.org&utm_campaign=e878a35206-RSS_VIDEO_DAILY&utm_mediu
Paul Rogers
Manager
"It seems amazing to me that on their limited diet, the hunter-gatherers still managed equal energy expenditure and far greater levels of physical activity than well-fed Americans. They exist on limited calories but maintain high levels of physical activity while the latter takes in copious calories and has little physical activity, despite similar levels of total energy expenditure."
Completely misinterpreted I feel. Please explain why you think this would be so.
Gil Hardwick
Anthropologist
Yes, I agree that it is sedentary lifetstyle and its contingent inactivity that is at the root of this 'obesity'. I do not find the conclusions counter-intuitive, perhaps because my long-term ethnographic background living with others and then returning to fat and lazy so-called 'civilisation' gives me a stark contrast.
Consider that it is not simply being sedentary, not having to think or worry about where your next meal is coming from so you don't have to go find food every day. You are also…
Read moreSteve Brown
logged in via email @yahoo.com.au
"Yes, I agree that it is sedentary lifetstyle and its contingent inactivity that is at the root of this 'obesity'."
We're yet to see proof of this claim. The researchers just point to a correlation and then leave out the most important bit: evidence to link the two (obesity and a sedentary lifestyle).
Aside from all the data showing that it's the modern industrial concoctions passed off as 'foods' which are causing all these problems, the 'lack of activity' explanation has always struck me as patently absurd- all of a sudden in the last 15 years we became lazy, gluttonous pigs?
Check out countries which don't have an obesity problem, like France. They don't do more exercise than us.
Alice Gorman
Lecturer in Archaeology at Flinders University
There are virtually no hunter-gatherer groups today who have not been impacted heavily by local and European colonialism, which frequently involves them being reduced to living in marginal lands with poor resources. In Africa there are decades-long efforts to deprive hunter-gatherers of their land by Indigenous governments. In Africa and other parts of the world there are also complex social and economic relationships between hunter-gatherers and agricultural/urban groups, with much movement between them. Analogies with hunter-gatherers have to take account of the fact that contemporary groups cannot be mapped exactly onto presumed past behaviours.
The introduction of refined sugar into the everyday European diet as a result of the plantation economy (which also contributed to the dislocation of Indigenous societies in Africa, South America and the Caribbean) had a massive impact on dental health as well as changing the composition of diet.
Peter Gerard
Retired medical practitioner
If we put to one side genetic influences in respect to thinness and fatness[ and they are important, especially in some ethnic groups] the main reason for the obesity epidemic is excessive calorie intake. Exercise is important but is secondary to calories. It used to be said, that to expend the extra energy from one Mars bar, you would have to climb up and down the Eiffel Tower. People tend to put on weight slowly, almost imperceptibly, and over 6-12 months you are shocked at what the mirror or scales…
Read more