"Eating with familiar others has a powerful effect of increasing food intakes." Except when women eat in the company of men.

A systematic review and meta-analysis of the social facilitation of eating. Helen K Ruddock, Jeffrey M Brunstrom, Lenny R Vartanian, Suzanne Higgs. The American Journal of Clinical Nutrition, nqz155, August 21 2019, https://doi.org/10.1093/ajcn/nqz155

ABSTRACT
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.

Keywords: social facilitation, social influences, food intake, food choice, meta-analysis