Friday, August 3, 2012

That hunter/gatherer diet / activity study...not what it seemed

There was a lot of reporting in the last week about a study which many interpreted as saying that because it looked like a certain hunter gatherer population had activity levels similar to those of modern people then the modern obesity epidemic must be all about diet....

Dr Briffa certainly interpreted it that way - this evidence points away from differences in activity and energy expenditure as being a major explanation for why hunter-gatherer populations tend to be much lighter than those living a more Westernised existence - as did the Daily Mail.

It is not as straight forward as that of never is.  Health Uncut point out three flaws in the paper, "sealing its place in the realm of fiction"

1)    The study was a population of only 30 people, and of these 17 were women, who had NO statistically significant increase in physical activity levels versus Western women. That’s right in a study comparing the effects of high versus low activity levels of two populations; there was no actual difference in the levels for over half the group. Makes it interesting to wonder how they could expect to find a difference.
2)    The average BMI of the Western population was just over 25, so not an obese population, and depending on fat distribution, not an ‘overweight population’ either. Basically, we are comparing apple brands, and asking which makes the tastiest orange juice.
3)    Lastly, the study does not describe the calorie intake of the Hunter Gatherers. What we do see is a small population bordering on underweight status. So most likely they have low caloric intake. And, what does low caloric intake i.e. dieting do, it lowers total energy expenditure (hence the flaw in dieting). So are we surprised with these inconsequential findings?

As we describe in The Health Delusion, such is the age of sloth we live in, that in order to match our 1950s counterparts when it comes to physical activity, the average person would need to run a marathon each week.
In a world where there are already too few hours in the day, the last thing we want to hear is that we need to set aside more time to being more active, when we could actually free up time by just skipping a meal. And, so the market is open to all the diet gurus’ to pander to what interests us, instead of what is in our interest. But nature is a strict mother of principal, and does not cave in to our whimsies, whinging and tantrums to get what we want on our own terms. When you sooner or later join the 99% of people who find out dieting is ineffective for weight loss ask yourself this; if you don’t have time to be physically active now, how will you make the time for all that disease and illness in later life? 

The NHS Choices website also has a good analysis of the study:

Independent of its role in weight management, physical activity is also important to keep the heart healthy and to promote mental wellbeing. 
It should be noted that the study had some limitations:
  • its assessment of energy expenditure and other factors was based on only 30 Hadza adults
  • its assessment was also short term, carried out over an 11-day period
  • the data it used for comparison of the Hadza with Western and other populations was taken from several different sources, including some small studies of individuals (one such study included just 68 adults)
As the authors point out, this study only measured energy expenditure between different populations. This study does not examine the effects of changing levels of physical activity on obesity and did not report the long-term dietary patterns or calorie intakes of the people studied. It therefore cannot answer the question of which is more important, a calorie-dense diet or lack of physical activity as a cause of obesity. 
It does not address the important public health question of how best to combat rising overweight and obesity levels 
It is well recognised that weight loss may be difficult to achieve and even more difficult to maintain. Research on the most effective way to address this issue is urgently needed

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