Introduction
In field situations it is often desirable to obtain information, derived from either measurements of food intake or of energy expenditure, or of both, which will then be used in an overall assessment of nutritional status.
It may appear necessary, in this context, to attempt to measure whether or not individuals are in energy balance, i.e. whether the intake of energy in the food equals the energy expended in the normal routine of daily life.
A problem of considerable magnitude in the precise analysis of energy balance in natural. Free-living situations relates to the methods used in its measurement. Unless energy balance is being assessed at a very superficial level solely on the basis of the maintenance of constant body weight, which will be informative about will not us at what level it is occurring nor what adjustments in intake or expenditure may have occurred, measurement of both energy intake and energy expenditure are required. It is not intended to deal here with all of the details of the various methodologies, some of which have been described and analyzed elsewhere (1).However, some perhaps contentious conclusions can be drawn from some of our own recent data, not previously documented, which have become possible because of the unusual nature of the study – a series of repeated measures of all the various factors concerned in energy balance in a group of pregnant women studied longitudinally.
It has been long accepted that there may be considerable discrepancy in the agreement between energy intakes and expenditures of individuals, or even of groups, when these are measured during several consecutive days. Durnin (2) in 1961 showed that only 5% of a group of 69 men and women had intakes of energy which were closely related. On a day-to-day basis with expenditures. On a weekly basis about 60% of the individuals reached agreement between the two. The remainder demonstrated no relationship during 7 days between intake and expenditure of energy. There are also not notorious examples of marked discrepancy even in groups of people between their mean intakes and expenditures of energy without any obvious explanation.Norgan et al (3) in a study on 2 village populations in New Guinea, one being a coastal and the other a highland group, obtained very similar results for energy intake and expanditure in the highland group for both men and women, but there was a difference of about 500 kcal/d (2.1MJ)between the two sets of measurements in both men and women in the coastal village village. The methodology was exactly the same in both situations and there seemed no adequate explanation because of season, work, food availability, changing body weight, etc. These incompatabilities between intakes and expenditures have been a source of anxiety but have usually been shrugged off as being a reflection of the probability that measurements on an individual (or on groups of individuals), carried out during short period of time, might well not be expected to agree because of normal variability, from day or from week to week in both food intakes and physical activity. The resultant small alterations in body mass and body composition caused by these short-term energy imbalances, would be too fine to measure – the methodology in this field is too imprecise to detect small variations if this nature.However, studies which have been briefly described recently (4) give grounds for deeper concern about the used and limitations of measuring energy expenditure.
