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413. Hunter-Gatherer Energetics and Human Obesity

DOCUMENT TYPE
Research Article
AUTHOR
Herman Pontzer, David A. Raichlen, Brian M. Wood, Audax Z. P. Mabulla, Susan B. Racette, Frank W. Marlowe
DATE
August 2012

Commentary: Adrian Bauman, Cluster for Physical Activity and Health (CPAH), University of Sydney

This paper on the energy expenditure in Hunter Gather populations compares them with farmers and with western developed populations.  The study is by a group of anthropologists from the USA. They measured the Hadza people, a Hunter Gather population in Northern Tanzania.  This important work examines total energy expenditure (TEE) and possible reasons for obesity in industrialised society where energy expenditure is less than energy intake is greater.

The study looked at a sample of 17 women and 13 men in the Hadza Community and measured obesity, and TEE using doubly labelled water. The Hadza people were generally thin by western standards, with a mean body mass index of around 20 for men and women.  Their percent body fat was also substantially lower than western populations. The total energy expenditure in kilocalories per day was not very different to Western populations, but these Hadza adults were much leaner. Two consequences of this were noted. The first which is their physical activity level, (PAL) which is the ratio of their total energy expenditure to their basal metabolic rate was substantially higher than western populations. Hadza women had a PAL of almost 1.8 and men almost 2.3 which are substantially higher than 1.7 for women and 1.8 for men observed in western populations. This means they were more physically active, particularly men as they had to go out into the bush and forage for food and hunt.  Their total energy expenditure was relatively similar; partly because they weighed substantially less and nobody in this population was overweight [highest BMI amongst any Hazda adults was one BMI of 23.9]. The second reason they suggest is an anthropological one, which is that it may be an evolutionary trait of humans to have relatively stable total energy expenditure.

They do show relationships between fat free mass and total daily energy expenditure, and they show this in a number of ways. This suggests that there is an inverse relationship, the more energy you expend the lower your body mass, despite the fact that your total energy expenditure may be relatively stable. This is an anthropological perspective, which is quite different to our usual thinking about total energy expenditure and obesity. Nonetheless these Hadza men and women were much more physically active, and that is an important component, as they needed to walked long distances each day – over 11 kilometres for males. This equates to something around 15,000 steps per day which is much more than we typically do in western countries.

In summary this paper challenges us from an anthropological level to think about evolutionary biology and its relationship to energy expenditure. It also points to the fact that if you have a heavier population the total energy expenditure will be higher because it takes more energy to move them. Not surprisingly, hunter gathers are much more physically active than other populations and this undoubtedly contributes to their health in a number of ways.  But in terms of obeseogenesis, it maybe there are evolutionary and biological regulatory mechanisms at play, and that the amount of additional food eaten has a substantial role, given baseline physical activity levels at any level in contributing to obesity. Once again this reinforces the importance of food intake in obesogenesis, but does not negate the health consequences of inactivity at any level of industrialisation.

Source: PLOS One, 2012:7: e40503. Access to this article will depend on your institutional rights.  Click here to access the full article.