How many calories should each one of us be burning? How many calories were we evolved to burn?
And if we habitually burn under or over that genetic sweet-spot will there be health consequences?
Work hard, get ripped.
One group of researchers wrote an essay about the nutrition of Victorian Englishmen:
Their levels of physical activity and hence calorific intakes were approximately twice ours.
They estimate it as follows:
Using average figures for work-related calorie consumption, men required between 280 (walking) and 440 calories (heavy yard work) per hour; with women requiring between 260 and 350 calories per hour. This gives calorific expenditure ranges during the working week of between 3,000 to 4,500 calories /day (men) and 2,750 to 3,500 (women).
We found that despite all this 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.
Therefore, far lower than that purportedly consumed by Victorians.
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. […]
Our findings add to a growing body of evidence suggesting that energy expenditure is consistent across a broad range of lifestyles and cultures.
The conclusion doesn't 'feel' right. Hunter-gatherers need to do a lot more work just to eat than we do. It also does not quite sit with what the authors of the Victorian essay concluded.
Coming home from the shopping mall.
The researchers undertook their study during 11 days over the dry season. Would their results be similar if they undertook it over the wet season? And if they followed the tribesmen all year, would the results have been different? According to Wikipedia the diet and the activity of the Hadza are different during the wet season:
During the wet season, the diet is composed mostly of honey, some fruit, tubers, and occasional meat. The contribution of meat to the diet increases in the dry season, when game become concentrated around sources of water.
Perhaps most interestingly, the authors not only plotted energy expenditures against Westerners, but also against a group of Bolivian farmers. These had significantly higher energy expenditure.
To get a few more ideas about this, I had a look at "The Logistics of the Roman Army at War: 264 B.C. - A.D. 235" by Johnathon Roth. Roth considers what the energy requirements of a Roman (and therefore, as far as I am concerned, ancestral) soldier might have been.
Rations for Roman soldiers were two sextarii of grain per day, about 1.08 litres or 800 grams of wheat. Additionally, they probably ate half-pound of meat a day, around 190 calories of legumes (page 34), 100 calories worth of cheese, 1 1/2 ounces of olive oil for 360 calories. On page 39, Roth estimates they would consume, on average, 0.54 litres of wine, for around 350 calories. This all amounts to around 3390 calories/day (page 43).
On page 12, Roth calculates that an average soldier would be 66kg. Assuming 12% bodyfat, that would be 58kg of lean mass and meant the soldier would be burning 58.4 Calories/kg
I've plotted the Roman soldier (green) and a 5'6" Victorian with a BMI of 23 (yellow) on the graph provided by the Hadza study team for energy versus body mass. Both are above the trend line. In fact, the averages for all agricultural populations are above both the trend lines. That tells us something. But what?
Agricultural Populations seem to have higher energy expenditures either than us or the Hadza hunter-gatherers.