The fittest guy on my RN aircrew survival course was a wiry, cross-country running, rock-climbing enthusiast. The least fit was at least one stone overweight, probably two.
Imagine a cold, snowy February, OK, only the New Forest, not the Cairngorms, but still brassy. And who got mild hypothermia and had to be "nursed" through the next couple of days until the weather warmed up?
That's right, the fitness freak. The lardy one just lost a stone, and continued chortling.