Body composition at menarche: The Frisch-Revelle hypothesis revisited.

Figures for height and weight and derived values for total body water and fat were assembled for groups of girls with a variety of disorders to examine their conformity to the hypothesis of Frisch and Revelle that menarche occurs at a "critical" weight associated with a decline in metabolic rate and achievement of a characteristic body composition. The groups examined included girls with unusually tall stature, central idiopathic precocity, precocity associated with hypothyroidism, girls with hypothyroidism but lacking signs of sexual maturation, one group with gonadal dysgenesis, and another of girls with obesity. Girls with tall stature significantly exceeded the "critical" weight of 47.8 kg before achieving menarche but had onset of menses in accordance with the body composition hypothesis. The body composition of girls with idiopathic sex precocity was altered toward that at menarche of normals although the patients were much smaller and younger. The same trend was exaggerated in girls in whom precocity was associated with hypothyroidism; equally hypothyroid girls showing no signs of adolescent development had body compositions similar to those of age-matched controls. Girls with gonadal dysgenesis showed an alteration in body composition paralleling that of normals between the ages when the latter begin the pubertal growth spurt and achieve menarche. Girls under 8 years of age with simple obesity had an even greater percentage of body fat than normal menarchal girls but showed no signs of puberty. It is concluded that menarche is not necessarily triggered by achievement of a critical body weight or lowering of metabolism. Neither are the rising levels of estrogen in adolescence solely responsible for the characteristic increase in body fat. Only the data on girls with obesity failed to accord with the generalization that, when the ovaries are competent, menarche is highly correlated with achievement of a characteristic body composition. The observations, particularly in gonadal dysgenesis, suggest the pituitary gonadotropins may play a role in determining body composition in menarche.