The relationship between nutrition and adolescent fertility has been a topic of much discussion in recent research on human biology. The apparent increase in the incidence of teenage pregnancy in Western societies has led some researchers to wonder whether there are biological as well as cultural factors that influence this phenomenon (Vinovskis 1988). Studies of adolescents in different geographic and socioeconomic settings have demonstrated that the age at which sexual maturity is reached is not fixed but is heavily shaped by numerous influences, such as fatness at adolescence, physique, health status, genetics, degree of physical activity, and socioeconomic status (Maresh 1972; Johnson 1974; Short 1976; Zacharias, Rand, and Wurtman 1976; Frisch 1978; Meyer et al. 1990; Moisan, Meyer, and Gingras 1990; Wellens et al. 1990).

Since the reproductive process requires energy, reproductive ability is curtailed in times of food scarcity or when calories burned through physical exertion or exercise exceed the amount provided by food intake. Undernourished women, for example, reach menarche later and experience menopause earlier than do well-nourished ones. Poorly nourished women also have higher frequencies of irregular menstruation and anovulatory menstrual cycles, with menstruation and ovulation disappearing entirely if malnutrition is severe. During pregnancy, malnourished women have a greater likelihood of miscarriage, and if they do carry the infant to term, they experience a longer period of lactational amenorrhea. In men, severe malnutrition leads to loss of libido, a decrease in prostate fluid and in sperm count and mobility, and, eventually, the loss of sperm production altogether. For children and adolescents, undernutrition delays the onset of puberty in both boys and girls, and limits the fecundity of those who have achieved sexual maturity (Frisch 1978).