Larger bodies retain more heat - heat production is proportional to body mass and heat loss proportional to skin surface. Volume to surface ratio favours large bodies in cold climates.

But you misunderstand my claim anyway. The claim is that among a ethnically homogeneous group of Swedes living in Sweden, those in relative poverty would grow to be shorter, on average, than wealthier ones.

En un viejo país ineficiente, algo así como España entre dos guerras civiles, poseer una casa y poca hacienda y memoria ninguna. -- Gil de Biedma