Possible errors in the practical application of the theoretical objective
A series of experiments we have recently carried out on pregnant women has allowed, possibly for the first time, a reasonably well-grounded value to be attached to one side of the quation involved in energy expenditure estimates can be compared (4). Measurements have been made on a group of 22 women, beginning from early pregnancy (6-10 weeks) and repeated at 6 weekly intervals throughout pregnancy,performed 5 to 6 times on each individual woman. The measurements each 6 weeks consisted of a weighed food intake, by the individual inventory method, during 5 consecutive days; energy expenditure during the same 5 days by a combination of an activity diary and indirect calorimetric measurements of the important activities; BMR measure in the laboratory; anthropometric measures of skinfolds, limb circumferences, skeletal diameters, height and weight; body fat by densitometry using the underwater weighing method; an exercise test on the treadmill; weekly body weights. There are various reasons why this particular situation should allow a better assessment of the validity and accuracy of moderate to long-term energy expenditure estimates. For one thing there is more than just a straight comparison between energy intake and energy expenditure, each measured during a few days.Almost without exception, all previous measurements of free-living individuals have been done in a state of equilibrium. That is, the measurements have been done on groups of farmers, or housewives, or office clerk, or shop workers, etc, during a limited period of time, (usually 5-7 consecutive days for each individual person), when these people have been in a more or less stabie state.For almost all the groups, mean energy intake and mean energy expenditure have agerred to within about+- 10% of each other and this has been assumed to give an indication of the approximate error of the method.
Even when the relevant values for individual men or women have not agreed. This has often been taken to imply only a temporary aberration of either intake or expenditure.
In the present instance the subjects are not in energy equilibrium.Over an interval of some months,changes have occurred in the energy equilibrium which have resulted in a measurable woman. She has produced a baby, whose weight was known exactly and whose body composition could be estimated with an unimportant small error. The weight of the placenta was taken at the time of delivery. The size of the uterus could be estimated to levels which would involve inaccuracies of no importance in energy balance. The change in body weight and in body fat of the mothers was measured, again with an error which, as discussed below and as is apparent from Tables 1 to 4 is not relevant to the main conclusions.
Therefore, from all these measures, it was possible to calculate the overall energy required to effect these changes ( the energy cost of depositing the protein and the fat components were calculated separately).
Food intake was measured by the woman herself, each individual weighing all of the different items of food eaten or drunk during each period of 5 days. With modern electronic scales, incorporating a zeroing button, and having a large digital read-out, it became a simple and almost automatic procedure for the women,especially since this was done 5 or 6 times during the pregnancy. Our impression was that the individual subject undertook this task with high levels of accuracy.
Our conclusion is that the energy intakes and the separated energy costs of pregnancy were calculated with relatively small errors. Therefore, of energy expenditures could also have been assessed similarly, there should have been reasonable agreement between both sides of energy equation: i.e. the differences between energy intake and energy expenditures should have equalled the total energy costs of pregnancy.
