In pregnancy, total energy expenditure (TEE) has been estimated by respiratory calorimetry or by using a doubly labeled water method (DLW) [14, 15]. Whole-room, 24-h respiratory calorimetry demonstrates changes in the components of TEE under standardized protocols, e.g., sedentary conditions and minimal daily energy expenditure for basic survival, but makes no allowance for free-living physical activity. The DLW method, complemented with a measure of BMR, provides a quantitative estimate of the amount of energy expended in physical activity (AEE).
Whole-room respiration calorimetry studies carried out in well-nourished women [28, 29, 37] revealed that EE increases above prepregnancy values on average by 1, 4, and 20% in the first, second, and third trimesters, respectively. This increment was due largely to the increase in BMR.
Free-living TEE has been measured by DLW in well-nourished women [15, 30-33]. In these studies, TEE increased on average by 1, 6, and 19% over baseline values in the first, second, and third trimesters. Furthermore, BMR increased by 2, 9, and 24%, and AEE (TEE - BMR) changed by -2, 3, and 6% relative to baseline. On the basis of the larger increment in BMR, physical activity decreased as pregnancy advanced. These findings support the idea that women may conserve energy by reducing the pace or the intensity with which an activity is performed. Pregnant women may also change their activity patterns and thereby reduce the amount of time spent in activities. However, reduction in physical activity does not compensate for increases in BMR and energy deposited in maternal and fetal tissues. Thus, extra dietary energy is ordinarily required as pregnancy progresses .
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