The spontaneous intake of food, self-rated moods, and hunger of underweight women

A systematic review and meta-analysis of the social facilitation of eating

BACKGROUND

Research suggests that people tend to eat more when eating with other people, compared with when they eat alone, and this is known as the social facilitation of eating. However, little is known about when and why this phenomenon occurs.

OBJECTIVES

This review aimed to quantify the evidence for social facilitation of eating and identify moderating factors and underlying mechanisms.

METHODS

We systematically reviewed studies that used experimental and nonexperimental approaches to examine food intake/food choice as a function of the number of co-eaters. The following databases were searched during April 2019: PsychInfo, Embase, Medline, and Social Sciences Citation Index. Studies that used naturalistic techniques were narratively synthesized, and meta-analyses were conducted to synthesize results from experimental studies.

RESULTS

We reviewed 42 studies. We found strong evidence that people select and eat more when eating with friends, compared with when they eat alone [Z = 5.32; P < 0.001; standardized mean difference (SMD) = 0.76; 95% CI: 0.48, 1.03]. The meta-analysis revealed no evidence for social facilitation across studies that had examined food intake when participants ate alone or with strangers/acquaintances (Z = 1.32; P = 0.19; SMD = 0.21, 95% CI: -0.10, 0.51). There was some evidence that the social facilitation of eating is moderated by gender, weight status, and food type. However, this evidence was limited by a lack of experimental research examining the moderating effect of these factors on the social facilitation of eating among friends. In 2 studies, there was evidence that the effect of the social context on eating may be partly mediated by longer meal durations and the perceived appropriateness of eating.

CONCLUSIONS

Findings suggest that eating with others increases food intake relative to eating alone, and this is moderated by the familiarity of co-eaters. The review identifies potential mechanisms for the social facilitation of eating and highlights the need for further research to establish mediating factors. Finally, we propose a new theoretical framework in which we suggest that the social facilitation of eating has evolved as an efficient evolutionary adaptation.

Dietary restraint and self-reported meal sizes: diary studies with differentially informed consent

Psychometric methods were used to explore the reliability and criterion validity of self-reported food intake in studies of dietary restraint. In Study 1 the reliabilities over days of daily aggregate intakes and of intakes at meals at particular times of day were assessed in 7 day food diaries by 27 low-BMI females. The sizes of particular meals correlated poorly with each other and with the total of all other meals; daily aggregate intakes also had poor reliability (Cronbach's alpha). Individuals meal sizes were consistent from day to day, with high inter-correlations between meal sizes, high correlations between meals at particular times and the sum of the remainder and high reliabilities. Aggregate intake had moderate criterion validity. Of individual meals, only breakfast achieved criterion validity, but there was a significant cubic component in its relationship with restraint. In Study 2, young male and female participants with various BMIs, completed a food diary on a single day. Again, aggregate daily intake had low reliability. Total intake and breakfast both had criterion validity, dietary restraint correlating negatively with total intake and breakfast size in the whole sample and in females, but there were significant quadratic components in the relationships. In contrast, restraint correlated positively with lunch size in the whole sample and in males. The combination of low reliability of individual meals as estimates of total intake, and the low criterion validity of all meals except breakfast, suggests that it may be inappropriate to study dietary restraint using aggregate self-reported intake measures.