Fatness, Menarche, and Female Fertility

FATNESS, MENARCHE, AND FEMALE FERTILITY ROSE E. FRISCH* A high proportion of well-trained athletes [1-3], ballet dancers [4, 5], and women who diet excessively [6—8] have secondary or primary amenorrhea. Menarche may be delayed until as late as age 19 or 20 years [2-4]. The amenorrhea is usually reversible with weight gain, decreased exercise, or both [2, 4, 9]. Secondary amenorrhea occurs in dieting women when weight loss is in the range of 10 percent to 15 percent of normal weight for height [6, 7], which is equivalent to a loss of about one-third of body fat [6]. Primary amenorrhea (absence of menarche at age 16 or older) also occurs in association with excessive thinness [2, 4, 6]. These data suggest that a minimum level of body fat—that is, stored, easily mobilized energy—is necessary for the onset and maintenance of regular ovulatory menstrual cycles. Data on obese women show that excessive fatness also is associated with amenorrhea [10, 1 1], as Marshall and Peel [12] described for cattle almost a century ago. Both too much fat and too little fat are therefore associated with the disruption of the reproductive ability of women. I have proposed that these associations are causal and that the high percentage of body fat (about 26 percent to 28 percent) in the mature human female may influence reproduction directly [13—17]. It is hypothesized that both the absolute and relative amounts of fat are important, since the lean mass and the fat must be in a particular absolute as well as relative range, that is, the female must be big enough to reproduce successfully [13, 17]. The research on athletes reported here was sponsored by the Advanced Medical Research Foundation, Boston, Massachusetts. A John Simon Guggenheim Memorial Foundation fellowship (1975-1976) permitted the author full-time concentration on adipose tissue. The author rethanks the helpful colleagues listed in individual publications, thanks the coauthors of publications, and thanks Rosemary Kelly for typing the manuscript. ?Harvard Center for Population Studies, 9 Bow Street, Cambridge, Massachusetts 02138.© 1985 by The University of Chicago. AU rights reserved. 0031-5982/85/2804-0455 $01.00 Perspectives in Biology and Medicine, 28, 4 · Summer 1985 \ 61 1 IOO%r Percent Body Water \ 3 6 9 3 6 9 5 IO 20 30 40 50 60 70 80 90 BirthA6EYEARS Fig. 1.—Changes in body water as percentage of body weight throughout the life span and corresponding changes in the percentage of body fat. (Adapted from Friis-Hansen [25]. Reprinted with permission). Why Fat? Reproduction requires energy; a pregnancy requires about 50,000 calories over and above normal metabolic requirements [18, 19]. Lactation requires about 1,000 calories a day [19], In premodern times lactation was an essential part of reproduction. During growth, and while the reproductive system is slowly maturing, the body changes in composition, as well as in size and proportions. Direct measurements of body water of girls from birth to completion of growth show a continuous decline in the proportion ofbody water. This decrease is particularly rapid during the adolescent growth spurt in height and weight that precedes menarche [15]. The proportion ofbody water declines rapidly in these years because girls have a large relative increase in body fat [20] (fig. 1). Fat contains only about 10 percent water, compared with about 80 percent water in muscle and viscera and about 36 percent water in bone. At the completion of growth, between ages 16 and 18, the body of a well-nourished woman contains about 26 percent to 28 percent fat and about 52 percent water, whereas the body of a man at completion of growth contains about 14 percent fat and 61 percent water [20—25]. As shown in table 1, a young girl and boy of the same height and weight differ markedly in their percentages of body water and fat. The main function of the 16 kg of stored female fat, which is equivalent to 144,000 calories, may be to provide energy for a pregnancy and for about 3 months' lactation [5]. In prehistoric times 612 I Rose E. Frisch ¦ Fatness and Female Fertility TABLE 1 Ratio of Total...