maternal stress and fatigue associated with the demands of lactation and child care (Alder et al., 1986; Masters and Johnson, 1966).
Similar findings of reduced sexual response were reported by Kayner and Zagar (1983) among a self-selected group of lactating women whose nursing practices were judged to be intensive, based on reports of unrestricted nursing, frequent sleeping with the infant, and delayed introduction of formula or other food supplements for an average of 6.3 ± 1.99 (standard deviation) months. The period of amenorrhea was found to correlate strongly with the duration of reduced sexual desire.
Positive attitudes toward breastfeeding have been associated with the woman's comfort with her own sexuality (Newton, 1973), whereas negative feelings have been related to a dislike of nudity and sexual feelings (Newton and Newton, 1967). Thus, the positive association of breastfeeding and sexuality found by Masters and Johnson (1966) may be due in part to the highly self-selected nature of the breastfeeding sample used in their research. In addition, some women may meet their sensual and affectional needs by substituting breastfeeding and caretaking of infants for sexual activity (Kayner and Zagar, 1983; Lawrence, 1989; Waletsky, 1979).
The relationship of breastfeeding to female sexuality is therefore complex. The most informative studies thus far have included the collection of antenatal data, a longitudinal approach, and controls for socioeconomic factors. Further research should include those elements as well as controls for nursing intensity and evaluations of both endocrinologic responses and nonhormonal factors as determinants of sexuality.
No comprehensive studies have been conducted in humans to examine the long-term maternal consequences of lactation on the prevalence and severity of, or predisposition toward, obesity. Some studies have been conducted in animals to examine the effects of pregnancy not followed by lactation on maternal body composition. In humans, studies have focused on energy expenditure, adjustments in the metabolism of adipose tissue, and changes in body weight during lactation and on maternal body mass at various times after lactation has ceased. Changes in the pattern of maternal energy expenditure during lactation are reviewed in Chapter 5.
Studies in rats (Bogart et al., 1940; Jen et al., 1988; Moore and Brasel, 1984) indicate that pregnancy without subsequent lactation results in increased adipose tissue stores and increased fat cell numbers. Conversely, lactation