Why You Can’t Just “Work Off” That Ice Cream Sundae
Over-eating rather than inactivity could be the reason that, among Westerners, obesity is now talked about as a pandemic. Scientists from the US, Tanzania and the UK came to this conclusion not from analyzing health records or other data but studying the members of the Hadza tribe of Tanzania.
The Hadza, whose population is about 1,000, still live as hunter gatherers and scientists chose them as a model of ancient peoples as they do not use modern or guns but bows, small axes and digging sticks. They hunt animals and also forage for berries, roots and fruit on foot.
In the study, scientists measured the energy expenditure of 30 Hadza men and women (aged 18 to 75 years). As Dr Herman Pontzer of the department of anthropology at Hunter College, New York, said to the BBC, the assumption was that the Hadza burned “hundreds” more calories per day than the average American or Britain who (very often) works at a desk, can order lunch to be delivered and drives a car home.
To the scientists’ surprise, even though the participants’ activity level was far higher than that of most Westerners, “when corrected for size and weight, their metabolic rate was no different to that of Westerners.”
Pontzer was quick to emphasize that exercise and physical activity are key to overall health. But the study (published in the online scientific journal PLoS ONE) provides further clues about the West’s obesity pandemic. Said Pontzer:
“This to me says that the big reason that Westerners are getting fat is because we eat too much – it’s not because we exercise too little.
“Being active is really important to your health but it won’t keep you thin – we need to eat less to do that.
“Daily energy expenditure might be an evolved trait that has been shaped by evolution and is common among all people and not some simple reflection of our diverse lifestyles.”
The scientists emphasized that “active, ‘traditional’ lifestyles may not protect against obesity if diets change to promote increased caloric consumption” — that is, if people overeat, just being more physically active does not compensate for the extra calories and is not sufficient to fend off obesity.
The study also has important implications for efforts to supplement diets of people in developing regions. The authors point out that such efforts
…must avoid inundating these individuals with highly-processed, energy-dense but nutrient-poor foods. Since energy throughput in these populations is unlikely to burn the extra calories provided, such efforts may unintentionally increase the incidence of excess adiposity and associated metabolic complications such as insulin resistance. Indeed, processed, energy-dense foods have been linked to insulin resistance and cardiovascular disease among Australian foragers transitioning to village life.
Again, the researchers emphasized that exercise is certainly important in maintaining good health. Hadza men and women had lower rates of body fate than Westerners, for instance.
But if you’re thinking you can just “run off” a huge meal the next day, you may want to think twice.
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