There's a popular meme that we exercise less than a few decades ago, less than people in third world countries, that we are lazier and less active. It's not true.

There's a fascinating way to measure daily energy expenditure called Double-Labled Water Method. You lable the hydrogen and the oxygen, then over the days and weeks after the dose, measure the remaining labled atoms. The difference in the decreases of hydrogen vs. oxygen give you the measurement for calories used.

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Using this method over several decades, this researcher found that people world-wide use about the same amount of daily energy, and that this daily energy use is about the same as it was in the eighties. If anything, North Americans have increased their daily energy use slightly. If you take various wild mammals, their energy use varies by body size and temperature. If you plot where humans would fall at a comfortable temperature of 20 C, then that's about where we are.

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I think that's pretty interesting, partly because it contradicts common wisdom.