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Abstract

Reproduction places severe demands on the energy metabolism in human females. When physical work entails higher energy expenditure, not enough energy will be left for the support of the reproductive processes and temporal suppression of the reproductive function is expected. While energy needed for reproduction may be obtained by increases in energy intake, utilization of fat reserves, or reallocation of energy from basal metabolism, several environmental or physiological constraints render such solutions unlikely. For human ancestors increases in energy intake were limited by availability of food, by labor of food preparation and by metabolic ceilings to energy assimilation. Energy stored as fat may support only a fraction of the requirements for reproduction (especially lactation). Effects of intense physical activity on basal metabolism may also interfere with fat accumulation during pregnancy. Finally, the female physiology may experience demands on increasing the basal metabolism as a consequence of physical activity and, at the same time, on decreasing the basal metabolism, when energy to support the ongoing pregnancy or lactation is inadequate. The resulting metabolic dilemmas could constitute a plausible cause for the occurrence of reproductive suppression in response to physical activity. It is, therefore, likely that allocating enough energy to the reproductive processes during periods when energy expenditure rises may be difficult due to physiological and bioenergetic constraints. Females attempting pregnancy in such conditions may compromise their lifetime reproductive output. A reproductive suppression occurring in low energy availability situations may thus represent an adaptive rather then a pathological response.

Disgust sensitivity in relation to menstrual cycle phase in women with and without an infection

“…Furthermore, there is a large variation in progesterone levels among individuals and between individual cycles, even in women who have regular ovulatory cycles (Jasienska, Bribiescas, Furberg, Helle, & Nunez-de la Mora, 2017;Jasienska & Jasienski, 2008). Levels of ovarian hormones in a cycle are influenced by many factors, including genetics (Jasienska & Ellison, 1998), developmental conditions , and adult lifestyle (Ellison, 2003;Jasienska, 2003Jasienska, , 2013Jasienska & Ellison, 1998Ziomkiewicz, Ellison, Lipson, Thune, & Jasienska, 2008).…”

Crucial Contributions

“…Therefore, both the length of pregnancy and the length of lactational amenorrhea are sensitive to maternal energy balance (Ellison 2003; Valeggia and Ellison 2009). That balance is a function of a woman’s current condition and the level of energetic stress she experiences (Jasienska 2003; Valeggia and Ellison 2001). For example, changes in ovarian function occur seasonally in concert with variations in women’s workload (Jasienska and Ellison 2004; Panter-Brick and Ellison 1994) and where seasonal food shortages are common (Bailey et al 1992).…”

An Energy-Saving Development Initiative Increases Birth Rate and Childhood Malnutrition in Rural Ethiopia

“…Life history theory predicts that any increased energetic efficiency for women should increase reproductive function in a resource-limited natural fertility population. Variations in human fertility in response to energetic stress can be seen to represent an evolved feature of women's reproductive systems, designed to enhance lifetime reproductive success by avoiding wasteful allocation of energy to reproductive opportunities with diminished chances of success [ 22, 23]. …”