How can energy balance be achieved by free-living human subjects?

Human subjects in modern affluent environments ingest nutrients in a variety of complex situations which contain stimuli that can have major effects on intake.These include the immediate environmental, temporal, social and psychological stimuli and the properties of the foods.The immediate environment contains signals, both learned and unlearned that influence the amounts of nutrients ingested and food choices.These signals include location, companions, weather conditions, noise and even the distance of items from the subject (Engel 8z Hirsch, 1991).Temporal stimuli include stimuli associated with the hour of the day, the day of the week, the week of the month and the month of the year.The social context includes the influence of the presence of other people and culturally defined roles and expectations.Psychological stimuli include learning, subjective state and eating restraint.Finally, the foods and drinks themselves may vary markedly in their palatability, nutritional adequacy and energy content.Yet, in the face of all these potent influences on immediate-short-term intake, somehow intake is matched to expenditure.This results in, and is evidenced by, a stability in body weight.How this is accomplished is not known, and uncovering the mechanisms by which intake and expenditure are matched is a major challenge for students of nutrition and ingestive behaviour.In order to study how these various stimuli affect intake in normal human subjects free-living in their natural environments we have employed the diet-diary technique (de Castro, 1987a,b, 1991 a&, 1993a,b,c,d, 1994a,b,c; de Castro & Kreitzman, 1985; de Castro et al. 1986, 1990; de Castro & Elmore, 1988; de Castro & de Castro, 1989; de Castro & Brewer, 1992).In the usual protocol, the subjects record their intake for seven consecutive days during their everyday lives in a pocket-sized diary.They record in as detailed a manner as possible every item that they either eat or drink, the time they eat it, the amount they eat, how the food was prepared, and the social and environmental context (for detailed description and discussion of the diet-diary technique and its validity and reliability, see de Castro, 1994b).The records are analysed by computer, and overall and meal intakes recorded and studied.A variety of procedures are employed to encourage the accurate maintenance of records and ultimately the validity of measurement.These include rewards linked to accuracy of recording, corroboration by other individuals and most recently by having subjects photograph the meals.Including these pictures along with the diaries increases the estimates of intake by over 8 % (Fig. 1).