How can eating behavior be regulated in the complex environments of free-living humans?

The eating behavior of humans in their natural environments is complexly affected by a myriad of nutritional, physiological, psychological, sociological and cultural factors. We have employed the diet diary technique to document the influence of: the subjective states of hunger, the amount of food or fluid remaining in the stomach at the onset of ingestion, and its composition, the time of day, day of the week, phase of the moon, month of the year, the location, the number of other people present, the relationship of eating companions to the subject, dietary restraint, and eating disorders. Recently we have demonstrated, with twins, significant heritabilities for the amounts of foods and fluids ingested, independent of body size. By viewing behavior in freeliving conditions the relative importance of these factors in the determination of the amounts and timing of intake can be discerned and measured. The analysis indicates that immediate environmental psychological, social, and cultural stimuli exert powerful but short-lived effects on intake. Physiological stimuli, on the other hand, appear to influence intake subtly but persistently. Their influences are difficult to document on the short-term, but clear over long periods of time. Short-term intake for the most part would appear to be unregulated and allowed to vary spontaneously within a relatively wide range. Physiological variables appear to feed back after a delay of at least a day and usually longer to alter the overall level of intake bias. The persistent bias continues to shift intake, producing a cumulative net alteration of intake, while the effects of random short-term influences average over time, and result in no net effect on intake.