In this review of published work on energy intakes or expenditures of human groups or populations, considerable and unnecessary difficulty has frequently arisen in relation to relatively simple questions of the authors' methodology. It might be useful to set out some of the more obvious description which should be included in any publication on the measurement of energy intakes or expenditures in man.
Firstly it is helpful to understand exactly what was the purpose of the investigation and why a particular population has been selected. The method of selecting the individual subjects should then be explained, including the number originally chosen, the number actually measured and, when a difference exists between these two, also the reasons, together with some indication - even subjective - of whether the sample has consequently become biassed.
It is also desirable to know at what time of year the study took place and the total duration of all the field-work.
If a longitudinal component is present, it should be clearly described; i.e. did it apply to the whole population or only parts. If it was only a part of the total number of individuals, what was the cross-sectional element? Did the populations differ? What were the numbers in each of the cross-sectional and longitudinal parts? Some socio-economic information should be given, such as the living conditions of the subjects, their occupations, some general picture of the physical activity, whether food availability might have been restricted due to financial or other reasons, etc.
As far as measurements are concerned, it is essential to give age, sex, precise numbers of individuals in each of these categories, height, and weight. It is highly desirable to include skinfold thicknesses (using at least some of the standard sites) and even a rough assessment of nutritional status. Of the data which can be expressed mathematically, each separate group of individuals should have the mean value, the S.D. and the range.
To allow a correct interpretation of the results, it is critical to have a very precise description of how food intake was measured; what exactly was measured and by whom and how experienced were the observers. For example, if a 24 h recall was employed, it is well known that errors can sometimes be enormous and will not be distributed in a random fashion around a more-or-less correct mean. It is helpful to know who carried out the 24 h recall, where was it done, how long did it take, was a standardized procedure used, what was the experience of the observer, were repetitions made on other days, was the method validated using other techniques or cross-over questioning by different observers, etc.
When food intake was measured and recorded, what was the exact way in which the measurement was done? What was the precision of the frequently-quoted “household measures”? what kind of balances were provided? To what degree of exactitude were they read? Were they calibrated and how? Were other utensils (plates, containers, etc.) provided? What sort of log-books were used, and how did the subject record each item of food (e. g. in relation to composite dishes; and if sauces, etc. , were taken, were they measured separately? ).
Were instructions in the methodology given to the subjects in their own homes, in clinics, by writing, etc. ? Was any supervision employed during the study, and for how long and how often? How accurately were food and drink consumed outside the home assessed? What was the exact duration of the investigation on each individual? When this varied, it is not satisfactory to say such things as “the investigation was carried out for periods of between 3 and 42 days on the subjects”. Was the period of the measured food intake apparently representative of the normal or not?
As far as the calculation of the intake of energy and other nutrients, which tables were used and now ? For example some well-known tables give energy values for carbohydrate, fat, and protein which do not include losses in digestion and absorption. Were allowances made for this ? Sometimes duplicate samples of the diet have been measured for energy content by bomb calorimetry, but of course this can be a spuriously accurate procedure if it is not realised that the values obtained does not at all represent the available energy in the food as far as the body is concerned.
Some of the foregoing statements apply here also. As well as these, the method used to measure energy expenditure needs perhaps even more precise description than for energy intake. If a “diary-record” is used to obtain detailed information of how the 24 h of the average day is spent, it is necessary to know to what degree of exactitude this was done (e.g. in single minutes, in blocks of 5 or 10 min, etc. ), whether the diary is compiled by the subjects themselves or by observers, who were the observers ? How often was the accuracy of the diary checked and by whom ?
For the indirect calorimetric measurements themselves, were these done by a form of respirometer of Douglas bag, etc. ? What was the duration of the measurement? Was the activity standardized, or was it thought to be representative of the normal free-living situation ? Some indication should also be given of the range of activities measured and the number of measurements on each activity, preferably in tabular form. How was the volume of the expired air measured ? Were the instruments calibrated and how ? How was the sample of expired air collected for analysis ? How long did it have to remain in the collecting container before analysis ? What instruments were used for analysis and how were they calibrated ?
If published or unpublished values of energy costs have been used their source should be quoted and their adjustment for varying body size, etc. should be clearly defined.
The method adopted to evaluate energy expenditure during sleep must also be carefully explained. If measured Basal Metabolic Rate (BMR) is the value employed, accurate description of how and by which instrument it has been measured should be provided.
When alternative methods have been used to assess oxygen consumption (VO2), for example using relationships between heart rate (HR) and VO2, because of the potential gross inaccuracy of the method, exact details should be stated about how the individual relationships have obtained. Any other variants should similarly be clearly described.
