It's more about how light the body is than how efficient it is. Consider: the Tesla Model 3 has a range of 350 km, and a battery capacity of 50 kWh. That's a li

It's more about how light the body is than how efficient it is. Consider: the Tesla Model 3 has a range of 350 km, and a battery capacity of 50 kWh. That's a little more than seven km per kWh. So, less efficient than the human body, right? Well don't forget that its curb weight is 1,611 kg. If we assume that the marathoning human weighs 100 kg, then the Tesla weighs 16x as much. So to compare the performance pound for pound, we need to imagine the energy use of sixteen human runners (36kWh for 42km, or just a little more than 1kWh per km). Also, it would be travelling that range at a much higher velocity. Of course, its coefficient of drag is probably lower than that of sixteen human runners, but considering the humans are running at 15 km/h or so, and the Tesla would be travelling at closer to 100kmh, the velocity factor of the drag calculation would be 40x higher for the Tesla than the humans. So, even if you factor in the unfairness of having skin and hair and clothes, the humans are actually a good deal less energy efficient than the car. I just found this analysis interesting. Our machines are after all quite a bit more efficient than our bodies (for certain tasks, of course). But that doesn't detract from your point that the body is definitely more efficient than you want it to be when it comes to losing weight!