Why Fat The Energy Cost of Reproduction

A human pregnancy and lactation each have a high energy cost: A pregnancy requires approximately 336 MJ (74 000 kcal) in addition to normal metabolic requirements. Lactation requires approximately 2.5 MJ (600 kcal) per day. In premodern times, lactation was an essential part of reproduction.

While the reproductive system is slowly maturing during growth, 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 at ages 16-18 years show a continuous

Birth

Age (months) Age (years)

Birth

Age (months) Age (years)

Figure 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 B (1965) Hydrometry of growth and aging. In: Brozek J (ed.) Human Body Composition, vol. 7, Symposia of the Society for the Study of Human Biology, pp. 191-209. Oxford: Pergamon Press.)

decline in the proportion of body water because girls have a large relative increase in body fat (Figure 1). This decrease is particularly rapid during the adolescent growth spurt in height and weight, which precedes menarche.

At the completion of growth, between ages 16 and 18 years, the body of a well-nourished woman contains approximately 26-28% fat and approximately 52% water, whereas the body of a man at completion of growth contains approximately 12% fat and 61% water. A young girl and boy of the same height and weight (Table 1) differ markedly in the percentages of body water and fat. The main function of the 16 kg of stored female fat, which is equivalent to more than 600 MJ (144 000kcal), may be to provide energy for a pregnancy and for approximately 3 months of lactation. In prehistoric times when the food supply was scarce or fluctuated seasonally, stored fat would have been necessary for successful reproduction. Fat is the most labile component of body weight. Body fat therefore would reflect environmental changes in food supplies more rapidly than other tissues.

Pregnancy And Childbirth

Pregnancy And Childbirth

If Pregnancy Is Something That Frightens You, It's Time To Convert Your Fear Into Joy. Ready To Give Birth To A Child? Is The New Status Hitting Your State Of Mind? Are You Still Scared To Undergo All The Pain That Your Best Friend Underwent Just A Few Days Back? Not Convinced With The Answers Given By The Experts?

Get My Free Ebook


Post a comment