Social facilitation of the spontaneous meal size of humans occurs on both weekdays and weekends

The amount eaten by humans in spontaneously ingested meals is positively correlated with the number of other people present. This could be due to a social facilitation or may be produced as an artifact of a covariation produced by a third factor. Possible covariations produced by time and location of eating, alcohol intake, and snack/meal ingestion were investigated by paying 78 adult humans to maintain 7-day diaries of everything they ingested, when and where they ingested it, and the number of other people present. The results demonstrate that, although the covariances exist, they could not account for the social correlation. Strong, positive and significant correlations between meal size and the number of other people present were found separately for meals eaten during the breakfast period, the lunch period and the dinner period, eaten in restaurants, at home and elsewhere, eaten accompanied by alcohol intake or without alcohol, and for only snacks or only meals. The results suggest that the correlation results from a true social facilitation of eating and that this facilitation is an important determinant of eating regardless of whether alcohol is ingested with the meal, a snack or a meal is eaten and regardless of when or where it is eaten.

The amount eaten by humans in spontaneously ingested meals is positively correlated with the number of other people present. In order to investigate whether this social facilitation of eating was due to an increase in arousal, emotionality, hunger, or social interactions, analyses were performed on the data obtained from 82 adult humans. They were paid to maintain 7-day diaries of everything they ingested, when and where they ingested it, the number of other people present, and their subjective states of hunger, elation, and anxiety. The presence of other people was found to be associated with the duration of meals and not the rate of intake, whereas self-rated hunger was found to be associated with the rate of intake and not the duration of meals. Self-rated anxiety was not found to be associated with the number of people present, whereas self-rated elation was positively correlated with the presence of others. Multiple regression analyses suggested that the presence of other people facilitates intake and increases elation independently. It also suggested that social facilitation operates by independently increasing the size and the duration of meals and that it operates independently of the subjective state of the individual. These results contradict the predictions of increased arousal, increased hunger, and increased emotionality models but support attentional, disinhibitory, and time extension models of social facilitation.

The relationship between the subjective state of hunger and objective food intake was investigated using a diary self-report method. Thirty-one adult humans were paid to record in a diary, for 7 consecutive days, everything that they either ate or drank, the time that they ingested it, and how hungry they were on a seven point scale. The diary entries were encoded and entered into a computer. Meals were identified according to 5 different definitions and meal compositions, estimated stomach contents, and intermeal intervals calculated. Univariate and multiple linear regression predictions of self-reported hunger and meal size were calculated from these data. Self-reported hunger was found to be related negatively to the energy content and the proportion of protein in the stomach at the time of meal ingestion. Meal size was also found to be related to these same factors and also positively to self-rated hunger. These results suggest that protein has a unique satiating property beyond its contribution to total food energy. When self-rated hunger and the premeal stomach contents were all used in a multiple regression prediction of meal size the premeal stomach contents influence became nonsignificant leaving subjective hunger as the only significant predictor of meal size. These results suggest that subjective hunger represents an intermediary step in the cause-effect sequence between gut filling and cessation of meal ingestion.