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More evidence that diet, not lack of exercise, is fueling obesity epidemic

REUTERS/Andrew Burton
Energy-dense foods, like sugary sodas, likely contribute more to obesity than lack of exercise.

The idea that if you burn more calories than-you consume you’ll lose weight is the mainstay of most diet programs. And public health officials have long cited the developed world’s increasingly sedentary lifestyle as a key factor behind the global obesity epidemic of the past few decades.

But should we be giving diet (calories in) and exercise (calories out) equal weight in the fight against obesity? No, suggests a growing body of research. Regular exercise may be crucial for our physical and mental health, but it does little to fight obesity, these studies indicate. In other words, we’re not getting fat because we’re less physically active, but because we’re eating too much energy-dense foods, particularly foods high in sugar.

herman pontzer
Herman Pontzer

In a commentary published last Friday in the New York Times, Hunter College anthropologist Herman Pontzer offers yet another piece of evidence that debunks the idea that our sedentary lifestyles are a driving factor behind the obesity epidemic. He describes an intriguing study he and his colleagues recently conducted in Tanzania (and published earlier this summer in the journal PLoS ONE).

For the study, the researchers measured 11 days of energy expenditure of 30 members (13 men, 17 women) of north-central Tanzania’s Hadza community, one of the few remaining full-time hunter-gatherer societies in the world.

“The Hadza live in simple grass huts in the middle of a dry East African savanna,” explains Pontzer in the Times commentary. “They have no guns, vehicles, crops or livestock. Each day the women comb miles of hilly terrain, foraging for tubers, berries and other wild plant foods, often while carrying infants, firewood and water. Men set out alone most days to collect honey or hunt for game using handmade bows and poison-tipped arrows, often covering 15 to 20 miles.”

Would the Hadza — who live similarly to our ancient ancestors (and who never get obese) — expend more energy (calories) during their everyday activities than the rest of us do in our daily routine?

Writes Pontzer:

Previous attempts to quantify daily energy expenditure among hunter-gatherers have relied entirely on estimation. By contrast, our study used a technique that calculates the body’s rate of carbon dioxide production — and hence the calories burned per day — by tracking the depletion of two isotopes (deuterium and oxygen-18) in an individual’s urine over a two-week period. …

We found that despite all [the Hazda people’s] 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, asccounting 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.

How can that be? Here’s Pontzer’s explanation:

We think that the Hadzas’ bodies have adjusted to the higher activity levels required for hunting and gathering by spending less energy elsewhere. Even for very active people, physical activity accounts for only a small portion of daily energy expenditure; most energy is spent behind the scenes on the myriad unseen tasks that keep our cells humming and our support systems working. If the Hadza’s bodies somehow manage to spend less energy in those areas, they could easily accommodate the elevated energy demands of hunting and gathering. And indeed, studies reporting differences in metabolic-hormone profiles between traditional and Western populations support this idea (though more work is needed).

“Our findings add to a growing body of evidence suggesting that energy expenditure is consistent across a broad range of lifestyles and cultures,” Pontzer concludes.

You can read Pontzer’s commentary on the New York Times’ website. His study is available in full on the PLoS One website.

Comments (8)

  1. Submitted by Ross Williams on 08/27/2012 - 11:03 am.

    Not what you eat, but how much

    “In other words, we’re not getting fat because we’re less physically active, but because we’re eating too much energy-dense foods, particularly foods high in sugar.”

    I don’t think there is much evidence to support this hypothesis either. Instead the problem is that people eat too much. Whether its protein, fat or sugar may not matter.

    The most likely explanation for why people are eating more is convenience. It used to be that eating had barriers. At home, one had to buy the food, prepare and cook it. This was why people ate family meals. Going to a restaurant meant sitting down and waiting for the food to come.

    With convenience foods, no preparation or waiting is required. Its not surprising with that abundance of food instantly available almost anywhere, people are eating more.

    • Submitted by Lance Groth on 08/27/2012 - 12:41 pm.

      Not quite

      “Whether its protein, fat or sugar may not matter.”

      This simply isn’t true, particularly with regard to protein. You cannot get fat eating protein. It’s easy enough to test for yourself – eat nothing but protein for a couple of weeks. Eat as much as you want, but avoid all carbs & most fats. You will begin to lose weight, and surprisingly rapidly too, because your body will go into lipolysis/ketosis and burn stored fat for fuel. This is well established, and is why low-carb diets work – with the added benefit that because you’re consuming so much protein, you will not lose muscle mass. The body burns 3 kinds of fuel: carbs, alcohol, and fat, in descending order of metabolic preference. Eliminating carbs and alcohol forces the body to burn fat. A common mistake for low carb dieters is to eat too much fat – after all, it contains no carbs and thus is “legal”. However, ingesting too much fat means that the body will burn dietary fat rather than stored fat.

      Eating too many high-glycemic index carbs over a period of years and decades is bad because it leads to insulin resistance syndrome. The body can no longer process the carbs efficiently, the pancreas works too hard & basically wears itself out, and eventually the combination of weight gain and insulin resistance leads to type 2 diabetes. It is a metabolic disorder, not a disease, and can be controlled or even reversed by avoiding the carbs and getting the weight down, and getting exercise.

      Eating either too many high glycemic carbs or too much fat is undesirable. The key is to stick to low-glycemic (“healthy”) carbs and lean proteins, combined with sufficient exercise.

      • Submitted by Ross Williams on 08/27/2012 - 02:11 pm.

        No extreme really works.

        “‘You cannot get fat eating protein.”

        You can’t get fat eating just sugar either, you will die from lack of nutrition. Same with just fat.

        But we are considering obesity. If you eat 3600 extra calories in a week, it doesn’t really matter whether they were protein, sugar or fat. They will all be stored by the body as a pound of fat.

        I would be very careful of the current pop culture science around diet, whatever the current pop culture or its source. You need to establish a balanced diet on which you won’t gain weight and then live with it. That is very hard to do since most of our bodies adjust to encourage us to eat more when it is available than we will consume. It means you have to monitor everything you eat or you need to monitor your body and consciously adjust what you eat to avoid slowly adding fat.

        • Submitted by Paul Scott on 08/28/2012 - 07:38 am.

          still wrong, sadly!

          This isn’t true, which is surely unfortunate, because it seems very clean and manageable. See David Ludwig’s study recently widely reported here and elsewhere. The rate at which the body stores calories differs depending upon the source. The pitch here for moderation and balance is itself a culturally created value system. The body doesn’t randomly want calories because they are available, though that is also a popular tenet of dietary folk wisdom of the moment. The body wants calories because it is depleted of energy, and it is depleted of energy when it does not have energy available, thanks to the hormones that regulate fat metabolism.

      • Submitted by Paul Scott on 08/28/2012 - 08:39 am.

        well stated

        I would only add that dietary (including saturated) fat may be burned first, but a problem with the “eat lean protein” advice is that dietary fat is necessary — it slows the release of insulin, promotes satiety and has numerous health benefits.

  2. Submitted by Maria Jette on 08/27/2012 - 12:18 pm.

    New shopping list…

    Poison-tipped arrows

  3. Submitted by Paul Scott on 08/27/2012 - 12:38 pm.

    fascinating study

    He seems to have proven that one half of calories-in, calories-out is flawed (the latter), but his assumption that the first half still holds was given a beat down earlier this summer by David S. Ludwig….It’s the quality, not the quantity of calories.

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