The basic information can be obtained from measurements of energy intake, repeated on more than one occasion (e.g. a5-day survey repeated after an interval of several weeks), combined with long-term measurements of fluctuations in body weight. A regression line plotted for weekly or bi-weekly weights of an individual, taken during some months, will easily show whether body weight is stable or not. The energy intakes will indicate at what level the stability is occurring.
Undoubtedly, most surveys of this kind would, of necessity, be done on small numbers of individuals. This is a disadvantage, but it is better to accumulate, even slowly, more of this most important information than to continue with the acquisition of data which is not only very difficult to obtain in field conditions but which has very limited usefulness.
One can criticze, in the same fashion, the likely advantages of some of the newer techniques of determining oxygen consumption over long periods-several days- by carbon and oxygen labelling; such techniques may well end up as just temporarily interesting and expensive ways of validating energy intake measurements. What will be obtained will be an extimate of total oxygen consumption, allowing total energy expenditure to be calculated. However, there is still the problem of knowing how representative is that total value of energy expenditure relative to the normal long-term pattern of individual. And no breakdown of the activity pattern will have been obtained.
There are several areas within the subject of enrngy balance which could profitably be explored. Some of them require simple methodology : long-term measurements of body weight on various populations, particularly those nutritionally at risk, would provide evidence on the existence or fluctuations in energy balance. Repetitive measurements of food intake on those populations could supply valid evidence on the level of energy intake at which energy balance does (or does not) exist. Physical activity patterns, particularly in leisure time, could give an indication of whether a population might be in apparent energy balance but still have insufficient food energy available to allow for active leisure pursuits.
It is astonishing that reliable data on these subjects is so scarce, particulary when their nutritional and socio-anthropological importance for much of the world’s population is so evident.
