[_0w8t]

Just read hypothermics.com . Its author, Ray Cronise, has done a lot of measurements using proper equipment.

And anecdotaly I have a co-worker who was into serious climbing. Before a high climb like over 6km he on purpose typically gained like 5 kilos of weight and still came back learner from the trip. And he knows for sure that that was due to coldness as on much more physically demanding trips at warmer altitudes weight loss was much smaller.

[rjsw]

My understanding is that you also burn more energy at altitude.

This has been given as one of the problems that Scott faced when man-hauling sledges on the Antarctic plateau at 3000m.