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The basis of this question is a pair of newspaper articles that appeared in the Guardian just over a year apart. I know, it's not a scholarly journal, and the articles aren't remotely scientific.

The two articles highlight divergent conclusions between a pair of academics studying nutrition.

Charles Spence, an experimental psychologist at the University of Oxford, was paraphrased by the Guardian in June 2015 as advising that "eating alone will keep you trim":

We eat 35% more when with one other person, 75% more with three others and twice as much when there are seven or more diners.

By contrast, Loïc Bienassis, a researcher and historian at the European Institute of the History and Culture of Food, an organisation connected to the University of Francois Rabelais, was portrayed by the Guardian in April 2014 as supporting the idea that, "with its emphasis on sharing and togetherness, the French approach to food seems to help limit obesity":

People pay more attention to standards of nutrition in a group than on their own. We drink in moderation, try to have some of everything, avoid taking a third helping because we are being watched and judged by others. Which is not the case when we nibble on our own beside the fridge.

In both cases, hefty and irritating journalistic decontextualisation is evident (i.e. the researchers' reported views are probably only accurate in certain fairly narrow contexts, if at all; yet the journalists have presented them as though they are generally applicable).

Nevertheless, the apparent contradiction raises the query: is there any scientific evidence that social eating reduces the incidence of obesity compared to solitary eating, or vice versa; and if so, what is that evidence?

  • This may also be on-topic in Cognitive Sciences Stack Exchange. – IQAndreas Jun 3 '15 at 21:04
  • What exactly in those makes you say they "aren't remotely scientific"? Medical science journals accommodate case reports and even opinionated [re]views. You probably mean to say the evidence is not systematic or something like that. – Fizz Dec 25 '17 at 15:37
  • Also, everything in the answer you've accepted seems to be an observational study, which can never completely remove potential confounding variables. – Fizz Dec 25 '17 at 15:49
  • @Fizz, thanks for the question. I added that caveat to highlight that the two articles I linked to are journalistic rather than scientific. Specifically, the articles were written by journalists Amy Fleming and Anne Chemin respectively, who neither reported themselves to have any scientific credentials, nor presented their work as having been created in a scientific mode. Nor is the Guardian, in which those two articles were published, a scientific journal: it is just a (reputable) newspaper. – sampablokuper Dec 29 '17 at 1:53
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Obesity is influenced by several factors such as behavioral traits, social-environment and genetics and one of the social microenvironmental influences on obesity promoting behaviors is social eating.

Socially derived inhibitory norms can account for either increased or decreased intake in the presence of others, depending on how much the others eat and the extent to which one is eager to impress them.

There is reliable evidence that total energy intake at meals is significantly increased when eating in the presence of other people, a phenomenon termed “social facilitation” as per research mentioned below.

De Castro studied 63 adults who maintained a 7-day continuous food diary and recorded the number of people present at each meal. Results indicated that energy intake during meals that were eaten alone was significantly lower compared to energy intake during meals that were consumed in the presence of others. This was observed for total energy intake (410 vs. 591 kcals), carbohydrate intake (190 vs. 241 kcals), fat intake (157 vs. 230 kcals), and protein intake (65 vs. 100 kcals). Satiety ratings were 30 percent greater following meals eaten with others compared to meals eaten alone. Indeed, de Castro argued that physiological signals that relate to appetite and meal size can be overridden by social interactions. Specifically, they found that reported total energy intake at meals was positively correlated with time since prior meal consumption, but only for meals eaten alone. When others were present at meals, there was no longer a significant association, suggesting that post-prandial meal regulation may be “disrupted by the presence of other people".

Additional analyses of de Castro’s data indicated that the social facilitation effect was greater for meals consumed in the presence of a spouse, family member, or friend compared to less familiar or unknown companions, suggesting that enhanced social interactions and discussions were the underlying mechanisms.

Laboratory studies have also demonstrated this social facilitation phenomenon.

Edelman et al. showed that overweight and normal-weight subjects consumed more lasagna when eating in groups of 4 or 5 persons compared to when eating alone, and that there was no significant difference between the weight groups in terms of this phenomenon.

Klesges et al. documented the social facilitation effect in a restaurant setting, with the effect being more pronounced for women than men.

Kimm and Kissileff also demonstrated the social facilitation of eating in a cafeteria setting.

Several researchers have noted that during the last 25 years in US, portion sizes of commercially available foods have increased in parallel with the increase of the incidence of overweight and obesity. One study among men and women 19 to 80 years of age has found that the frequency of consuming restaurant food is positively associated with body fatness. Another study has found that, in women, frequent consumption of meals at fast food establishments is associated with increased BMI (kilograms per meters squared), and in men, eating at both restaurants and fast food establishments is associated with increased BMI. In the year 2000, Americans spent 47% of their food expenditures on foods consumed away from home, and this proportion continues to increase. When consumers eat away from home, they are offered a large variety of low-cost, energy dense foods in large portions; all of these factors may encourage overconsumption of energy and lead to obesity.

A study published in the American Journal of Clinical Nutrition finds that how much teens eat can be influenced by how much their friends weigh. In the study, kids were allowed to snack as much as they wanted while hanging out with a friend or with a peer they did not know. All the kids ate more when they were with a friend than with a stranger. Participants eating with a friend ate substantially more than did participants eating with an unfamiliar peer. Furthermore, overweight youth, but not nonoverweight youth, who ate with an overweight partner (friend or unfamiliar peer) consumed more food than did overweight participants who ate with a nonoverweight eating partner. Matching of intake was greater between friends than between unfamiliar peers.

In 2007, Harvard researcher Nicholas Christakis and his colleagues analyzed 32 years' worth of data from an interconnected social network of 12,000 adults and found that a person's chances of becoming obese increased 37% if a spouse had become obese, 40% if a sibling had and 57% if a friend had.

In a study published in October 2009 issue of Appetite, the influence of gender, group size and gender composition of groups of eaters on food selected for lunch and dinner (converted to total calories per meal) of 469 individuals (198 groups) in three large university cafeterias was investigated.

In dyads, women observed eating with a male companion chose foods of significantly lower caloric value than those observed eating with another woman. Overall, group size was not a significant predictor of calories, but women's calories were negatively predicted by numbers of men in the group, while the numbers of women in the group had a marginally significant positive impact on calorie estimates. Men's calorie totals were not affected by total numbers of men or women.

The mechanism which underlies social facilitation of eating has been termed “time-extension” and has received the most empirical support. Specifically, the presence of people at a meal lengthens meal time which, in turn, promotes further energy intake. The point is important because, "there is evidence that the tendency to eat with others may be genetically influenced. Thus, the fact that some individuals are more likely to eat in the presence of others may not be a random event; rather, eating in the presence of others may be a trait that is influenced by genes that indirectly promote social facilitation of eating at meals."

Results strongly suggest large portions chosen by others lead to greater consumption and smaller portion choices by others are associated with eating less and is qualified by the weight of the other person. If a heavy-set colleague eats a lot, he or she is a better lunch partner than a thin colleague who orders the same dish. By contrast, a thin colleague who eats lightly is more likely to cause others around them to order less. Thus, from the perspective of self-regulation, recognizing situations where you are likely to be vulnerable to overconsumption is important. Brent McFerran, 2010

Socially derived inhibitory norms can account for either increased or decreased intake in the presence of others, depending on how much the others eat and the extent to which one is eager to impress them. Herman, C. Peter, 2003

  • Thank you for the lengthy answer. The studies you've linked to address (North) American contexts, so I can't help wondering if the effects they report are in some way dependent on the national context (e.g. routine exposure to fast food advertisements, or to poor food at school, or whatever) that may be very different in France. – sampablokuper Jun 16 '15 at 9:33
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    Nevertheless, I'm going to mark this answer as "correct", because it does answer the question, is there any scientific evidence that social eating reduces the incidence of obesity compared to solitary eating, or vice versa; and if so, what is that evidence? – sampablokuper Jun 16 '15 at 11:02

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