The article by K Berneis et al. and that of B Geldszus et al., both of which are published in this issue of the European Journal of Endocrinology, are additional testimony to the impact of the discovery of leptin by JM Friedman and colleagues in December 1994 (1). Indeed, the finding that adipose tissue is producing a "satiety factor", presumably acting within the brain, has been a crucial advance which has given the obesity research field novel and widespread impetus. In placing leptin in the perspective of other observations made in obesity, the following comments have to be made.
The discovery of leptin provides firmer ground for the former concept of the existence of a loop system connecting the brain and the periphery, a system aimed at maintaining normal fuel and body weight homeostasis (2–4). Such a loop system comprises, at present, one hypothalamic neuropeptide, namely neuropeptide Y (NPY) (5)