Fat.

Fat has been a menace to longevity since biblical times, but detailed studies of its deposition and function in the perinatal period only began comparatively recently. The function of brown fat in thermogenesis as distinct from that of white fat as a reserve of energy is now clear, but not why the guinea pig and the human baby should be two of the very few land mammals to lay down white fat in their bodies before birth. How much of this fat crosses the placenta and how much is synthesized by the fetus? There is evidence that the amounts and timing of the two events may not be the same in the two species but the reasons behind the differences are not at all clear. Genetic obesity in many forms is well known in rodents. None of them have contributed much to paediatrics as yet, but the Egyptian sand rat has promising similarities to persons who develop obesity and diabetes in adult life and a comparison of their metabolism in early life might be a profitable exercise.