The Human Beast

Why we do what we do

Do Americans Eat More Than Hunter Gatherers?

What is the secret of hunter gatherer slimness?

In an era of super-size meals, and high-calorie foods, it might seem obvious that overweight Americans eat far more than scrawny hunter gatherers. The truth is surprising. Americans eat far less per pound body weight. Obesity may have little to do with diet.

Eating large meals may contribute to obesity, of course—but only if the people involved are inactive. This principle is familiar to beef farmers who fatten stock not just by over feeding but also by restricting movement.

What if you could eat as much as you wanted?!

You can—provided that you lead a sufficiently active lifestyle. For highly active individuals, overweight is not a problem, however much they eat. Even increasing their food intake by 50 percent has no impact on body weight.

In experiments where volunteers upped their food intake by 50 percent, there was no increase in body weight among individuals who are physically active in their normal daily lives (“non exercise” activity, 2). Of course the inactive individuals put on plenty of weight.

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Such experiments imply that the root cause of obesity is not eating too much but being insufficiently active. Stated another way, people living in subsistence societies experience little or no obesity because they lead a physically active lifestyle that defends them against overweight.

Skeptics like to point to the difficulty of making a living for subsistence people. Yet anthropologists have done extensive research on their diet and find that they eat plenty–in fact far more than we do.

Subsistence people eat more than Americans

People from subsistence societies are all lean and fit. Paradoxically,

the skinny peoples of the world eat more than the obese ones. Among hunter-gatherers, such as the Ache of Paraguay, the average man, at 150 lbs weighs substantially less than the average American man but consumes 3,300 calories (i.e. kilocalories) compared to just 2,700 for the average American male (and the same applies to women, 2).

How do the Ache manage to eat so much without getting overweight? The answer is that they are very active compared to us, using three times as much energy in physical activity as we do (about 1,800 calories compared to 600 for us). When we lead an active life, we are good at regulating our weight, regardless of how much we eat.

Farmers have long known that if you want to fatten a cow before slaughter the fastest method is by confining her in a small space with plenty of high-energy food. By restricting our own movement via a sedentary lifestyle we are doing the same to ourselves.

What is to be done

If you ask yourself what has really changed in the modern world, it is not that we are eating more than our subsistence ancestors but that we are moving less.

If we wanted to bring our activity level up to that of the Ache foragers, we would need to bump up our daily movement to the tune of 1,200 calories, or about four hours of moderate walking! That is eight times what the medical authorities are recommending.

The Ache are very physically active however and if we modeled ourselves after less active groups, like the !Kung of the Kalahari Desert in South Africa, we might get away with doing an additional 2 ½ hours of moderate exercise.

It still seems like a tall order. Yet, it is easily achievable. As I pointed out in an earlier post, we need to stop thinking of exercise as a form of penance for indulgence in food. Rather we should be engaged in physical activities that we actually enjoy, or at least that occur naturally in our daily routines.

That requires some redesign of the physical environment to promote walking, cycling, and so forth. I am thinking of more sidewalks, bike lanes, standing work stations, and so forth. More important, perhaps, the model to follow is of people who move around plenty in the course of their work day—as hunter gatherers do—rather than an athlete training to run a four-minute mile.

If that happy project were realized and we found ourselves with a greater level of physical activity that is essential for health in our species, then problems of obesity would fade. As we acquired forager-like toning and slenderness, the amount we ate would go up to match their elevated food consumption.

1. Levine, J. A., Eberhardt, N. L., and Jensen, M. D. (1999). Role of nonexercise activity thermogenesis in resistance to fat gain in humans. Science, 283, 212-214.

2. Cordain, L., Gotshall, S. W., Boyd Eaton, S, and Boyd Eaton, S., III (1998). Physical activity, energy expenditure and fitness: An evolutionary perspective. International Journal of Sports Medicine, 10, 328-335.

Nigel Barber, Ph.D., is an evolutionary psychologist as well as the author of Why Parents Matter and The Science of Romance, among other books.

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