There is a happy land in which obesity and heart disease are virtually unknown. That is the realm of subsistence humans who eat more than we do. Thanks to their active lifestyle hunter-gatherers are ideally lean, fit, and healthy (apart from ever-present animal attacks, parasites, and infections). How much exercise would we have to take to be as active as our foraging ancestors? How does this compare with medical advice about exercise?
Medical guidelines
Current medical guidelines identify a reasonable amount of exercise that can deliver substantial health benefits. In 1995, the American College of Sports Medicine (echoed a year later by the Surgeon General) recommended that adults should engage in moderate physical activity for 30 minutes each day. Moderate activity involves walking at three miles per hour, for example.
How close do the medical experts come to the physical activity level of people in subsistence societies? Fortunately anthropologists collect extensive information on the diet and food intake, as well as the body weights of their study populations. These data allow us to calculate how much energy a particular group uses on physical activity and to compare them with Americans.
How active are foragers?
Detailed research on two hunter-gatherer societies (or "foragers") allows us to calculate how active they are. These are the Ache of Paraguay and the !Kung of the Kalahari Desert in southern Africa. The !Kung are rather smaller (at about 100 lbs) and have comparatively low activity levels whereas the Ache are bigger (at about 130 lbs) and highly active thanks to their high birth rate.
A !Kung male uses about 2,200 (kilo)calories per day in total, almost exactly the same as a male office worker, whereas an Ache man uses some 3,300 calories in a day (1). Out of their respective total daily energy consumption, the !Kung use about 894 calories on physical activity (compared to 607 for office workers) whereas the Ache use a whopping 1772 calories this way.
Since the !Kung and Ache are so much lighter than Americans, it is important to take body weight into account. I did this by converting their energy consumption into number of miles walked (at a standard 3 mph) the point being that energy used in walking increases the more weight a person is carrying. Energy used for daily physical activity was equivalent to 10 miles walked for the Ache, 6.8 miles for the !Kung, and 3 miles for the Americans.
If Americans wanted to be as active as the !Kung, they would need to add the equivalent of 3.8 miles of walking to their daily activity. If they wanted to be as active as the Ache, they would need to hike 7 miles a day. Taking the average, if we wanted to be as active as foragers, we would add 5.4 miles.
Walking at 3 mph, this would take 1.8 hours. This is 3.6 times the half-hour the Surgeon General and other medical experts recommend.
Here we get to the military commander's problem. It is very easy to tell Americans to walk five miles per day. The commander charges over the top only to find there is no one behind him. It is true that most people would be a lot better off doing half an hour of moderate exercise daily compared to none. Yet, our bodies were designed for doing about four times this much activity and would likely be much healthier doing so.
Activity can be clocked up in many different ways, however, including the fidgeting typical of slender people (2). Or you can do something you enjoy.
An hour-and-a-half of shopping with a cart uses about the same amount of energy as walking 5 miles. Or an hour of digging in the garden. Or two hours playing music while standing. Or two hours of waiting on guests. Being as active as a forager is neither easy nor simple in the modern world but it might be worth the effort, mental as well as physical.
1. Cordoin, 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.
2. Levine, J. A. (2003). Non-exercise activity thermogenesis. Proceedings of the Nutrition Society, 62, 667-679.
