1. Broiler chickens were fed 60-100% of recommended energy intakes to study the effects of energy restriction on protein and fat retention. 2. At an energy retention of 179 kJ/kg W0.75 d, only protein was retained. At higher energy intakes, each increment in retention had a rather constant composition: about 85% energy in fat and 15% in protein. At lower energy intakes body fat was mobilised whereas protein was deposited. 3. The efficiencies of energy retention in protein and fat were estimated to be 0.66 and 0.86 respectively. 4. The rather constant composition of additional retained energy after additional energy supply provides an explanation for a linear relationship between energy intake and energy retention.

Energy metabolism was measured in 24 women before pregnancy and during lactation (2 mo postpartum). Resting metabolic rate (RMR) increased by 0.17 +/- 0.38 kJ/min and postprandial metabolic rate (PPMR) showed a similar increase (0.17 +/- 0.45 kJ/min). Thus, the thermic effect of the meal (PPMR minus RMR) was not affected by lactation. Between subjects, the lactation-induced increase in RMR appeared to be positively related to body weight. During lactation gross metabolic rates during cycling (CMR) were slightly reduced and net metabolic rates during cycling (CMR minus RMR) tended to decrease by 0.6 kJ/min at all workloads; however, the decrease was statistically significant only at the lowest workload. Changes in metabolic rate during the recovery period after exercise were not significant, but resembled changes in RMR rather than changes in CMR. We conclude that no major changes in metabolic efficiency occurred during lactation.

These urinary nitrogen excretion and nitrogen retention data show that when the dietary supply remains constant, nitrogen balance increases toward the end of pregnancy, suggesting a more efficient use of dietary protein later in pregnancy. Urinary 3-MeH and creatinine excretion indicated no change in protein metabolism.

To investigate changes in the thermic effect of a meal (TEM) during pregnancy, metabolic rate was measured in the fasting state and during the first 180 min after consumption of a standardized test meal in twenty-seven women before, and in each trimester of pregnancy. Resting metabolic rate (RMR) showed a steady increase over pregnancy: values in weeks 24 and 35 of pregnancy were significantly higher than the prepregnancy baseline (Tukey's studentized range test). The pattern of changes of postprandial metabolic rate (PPMR) was similar to that of RMR. Consequently TEM, calculated as PPMR minus RMR, did not change over pregnancy; mean T E M values (kJ/180 min) before and in weeks 13, 24 and 35 of pregnancy were 117.3 (SD 19.4), 116.4 (SD 23.7), 111.6 (SD 24.4) and 111.5 (SD 26.7) respectively. We consider changes in TEM of less than 15% to be of little importance physiologically. If true changes in TEM over pregnancy are 15 % or more we would have had a 90 % chance of observing significant changes in T E M in the present study, given the number of subjects and the methods used. Therefore, we conclude that no substantial reduction in TEM occurs during pregnancy. In the present study we tried to investigate whether TEM is reduced during pregnancy, using a longitudinal approach including baseline measurements which were carried out before the onset of pregnancy. The number of subjects in our study was sufficient to detect a 15 YO change in TEM with a statistical power of 90 %. Pregnancy S U B J E C T S A N D METHODS Study designResting MR (RMR), postprandial MR (PPMR) and body weight (BW) were measured in twenty-seven healthy Dutch women before, and in weeks 13,24 and 35 of pregnancy. TEM https://www.cambridge.org/core/terms. https://doi

To investigate changes in energy metabolism during pregnancy, complete 8-d energy balances were measured before pregnancy and at 12, 23, and 34 wk gestation in 12 healthy Dutch women. While for each individual woman experimental diets were kept constant throughout the study with average intakes of 8.76 +/- 0.92 MJ/d (before pregnancy), 8.72 +/- 1.08 MJ/d (week 12), 8.85 +/- 0.93 MJ/d (week 23), and 8.72 +/- 1.12 MJ/d (week 34), neither the digestibility nor the metabolizability of the supplied diets showed significant changes from before pregnancy (92.8% and 88.6%, respectively) throughout pregnancy (92.7% and 88.2%, respectively). Twenty-four-hour energy expenditure (24-h EE) increased significantly from 8.63 +/- 0.80 MJ/d (before pregnancy) to 8.73 +/- 1.15, 9.08 +/- 1.08, and 9.94 +/- 0.94 MJ/d in weeks 12, 23, and 34 of gestation, to the extent predictable from changes in resting metabolic rate so that in an experimental setting with physical activity and energy intake standardized there seems little scope for other adaptive mechanisms.