Eating in larger groups increases food consumption
Julie C Lumeng, Katherine H Hillman
............................................................... ............................................................... .....
See end of article for
Dr J C Lumeng, Center for
Human Growth and
Development, 300 North
Ingalls Building, 10th Floor,
University of Michigan, Ann
Arbor, Michigan 48109–
0406, USA; jlumeng@
Accepted 2 January 2007
Arch Dis Child 2007;92:384–387. doi: 10.1136/adc.2006.103259
Objective: To determine whether children’s food consumption is increased by the size of the group of children
in which they are eating.
Design: Crossover study.
Setting: University based preschool.
Participants: 54 children, aged 2.5–6.5 years.
Interventions: Each child ate a standardised snack in a group of three children, and in a group of nine
Main outcome measures: Amount each individual child consumed, in grams.
Results: Amount eaten and snack duration were correlated (r=0.71). The association between group size
and amount eaten differed in the short (,11.4 min) versus the long (>11.4 min) snacks (p=0.02 for the
interaction between group size and snack duration). During short snacks, there was no effect of group size on
amount eaten (16.7 (SD 11) g eaten in small groups vs 15.1 (6.6) g eaten in large groups, p=0.42). During
long snacks, large group size increased the amount eaten (34.5 (16) vs 26.5 (13.8), p=0.02). The group
size effect was partially explained by a shorter latency to begin eating, a faster eating rate and reduced social
interaction in larger groups.
Conclusions: Children consumed 30% more food when eating in a group of nine children than when eating in
a group of three children during longer snacks. Social facilitation of food consumption operates in preschool-
aged children. The group size effect merits consideration in creating eating behaviour interventions.
increase in a behaviour merely from the sight or sound of others
engaged in the same behaviour.2–5Eating behaviour is one of
the clearest demonstrations of the social facilitation effect, and
has been documented in animals6–10and adult humans
adults eat 30–50% more in groups than when alone.23Prior
human research has been limited by the fact that most studies
measured amount consumed only by self-report,11–19 21and the
group-eating situations were not always comparable to the
non-group situations with regard to environment or meal
content.16 24To our knowledge, social facilitation of eating
behaviour has not been investigated in children, nor has it been
examined through direct observation or measurement of
consumption in a natural setting.
There are two primary hypotheses in the literature for the
mechanism of the effect. The arousal hypothesis states that in
larger groups activation or arousal is greater, which results in a
faster eating rate and greater consumption.12 25The time
extension hypothesis states that larger group size increases
social interaction, which extends meal duration, increases the
length of time that the individual is in the presence of food, and
thereby increases the intake.1 12 26Under this hypothesis,
children eating in large groups would be more likely to remain
seated at the table socialising at the end of a meal, and thereby
continue to eat. The arousal hypothesis has primarily been used
to explain the phenomenon in animals, whereas the time
extension hypothesis has been invoked to explain the effect in
Understanding whether and how social facilitation operates
in young children has potential clinical application and
relevance. Childhood is theorised to be a critical period for
the development of lifelong eating habits which presumably are
associated with obesity risk. Along with the increase in
overweight prevalence among children,27there has also been
dults and animals consume more food when eating in the
presence of others than when eating alone.1This
phenomenon, termed social facilitation, is defined as an
an increase in the number of young children potentially eating
in group situations with peers, in that the proportion of
preschool-aged children attending childcare outside the home
has increased in the past 50 years from 11% in 1949 to 62%
The primary aim of this study was to determine whether
social facilitation by group size of amount consumed occurs in
children as it occurs in animals and adults. We hypothesised
that children would consume more when eating in a larger
group than when eating in a smaller group. The secondary aim
of this study was to identify mediators of the effect, if present.
We hypothesised that in children the effect would be mediated
by arousal and not by extension of meal duration because we
predicted that preschool-aged children would be unlikely to
remain seated at a table socialising at the end of a meal.
Fifty-four 2.5–6.5-year-old children attending a university-
based preschool participated in this study. Parents were told
that the study would evaluate the amount of food children
consumed while eating in smaller or larger groups of children,
and agreement to participate was nearly universal. The study
was approved by the University of Michigan Medical School
Institutional Review Board and written informed consent was
We aimed to study each child’s eating behaviour in two
conditions: eating in a small group (three children) and eating
in a large group (nine children). These group sizes were chosen
a priori based on the literature,23as well as on the practical
consideration that nine was the maximum number of children
who could reasonably be seated at the table simultaneously.
Children within each classroom, which were grouped by age,
were randomised into groups of three (small group condition).
These groups of three were randomly combined to form groups
of nine (large group condition). The identities of the other
children with whom a child ate were therefore held constant.
The order of participation in the small group condition versus
the large group condition was randomised. Of the 54 children,
17 participated in only one condition, owing to absences from
school or scheduling conflicts in the classroom. When this
occurred, another child in the classroom who consented was
included to form a complete group. Sixteen children were
included in additional sessions for this purpose, and therefore
had data for more than the two conditions originally assigned.
All of these data (108 observations) were included in the
analyses. For children participating in both conditions, the
mean (SD) interval between conditions was 25.3 (21.3) days.
Children who participated in only one condition did not differ
by age, race or sex from those who participated in both
A snack session, as opposed to a complete meal, was chosen as
the observation period because using only a single food
provided greater experimental control. Each child had fasted
at least 1.5 h before the snack session. The snack, served during
the regular snack time and supervised by the regular classroom
teachers and a familiar research assistant, was served in a quiet
room familiar to the children, but separate from the regular
classroom and without distractions. The snack consisted of
plain graham crackers (Keebler), with which all the children
were familiar as it was served regularly as a snack in the
preschool. Each child was given one whole graham cracker
sheet broken in half into two squares (6.466.4 cm; 32.5 calories
and 0.9 g of fat per square). Each portion was measured three
times on a scale (Salter) with an accuracy of ¡0.1 g, and the
average of these three weights was taken. The mean (SD)
weight per portion was 14 (0.1) g. The preschool required that
children be provided a beverage of the teacher’s choice at each
snack session. Each child drank the same beverage in both
conditions. In all, 32 children drank milk, 12 juice and 2 water.
Each snack session was videotaped. Two cameras were placed
unobtrusively in corners of the room, and children were
generally oblivious to their presence. Children were seated at
a child-sized table prearranged with the initial 14 g serving of
graham crackers on a small plate before them. An additional
51.1 (2.3) g of graham crackers per child was placed at the
centre of the table on a single plate in groups of three children,
and divided between two plates, one at each end of the table, in
groups of nine children. The children served themselves
additional portions, which they were accustomed to doing at
the preschool. There was no time or portion limit imposed, and
the children never consumed all the graham crackers available
at the table. One teacher sat at the table with the groups of
three children and two teachers sat with the groups of nine. The
teachers did not eat with the children.
Children were accustomed at the preschool to leaving the
table when finished and returning to activities in the classroom.
When a child finished his or her serving and neither left the
table nor reached for another serving, the teachers were
instructed to offer a prompt, as they would normally. The
teachers remained at the table until the last child had returned
to the classroom. Intake of each child was determined by
counting from the videotape the number of graham cracker
squares each child had eaten and weighing the remaining
crackers (or portions of crackers) on the child’s plate. We
encountered no discrepancies using this method to determine
Tapes were coded by two trained coders blind to study
hypotheses, and inter-rater reliability exceeded an intraclass
correlation coefficient of 0.7 for all measures. Snack duration
was defined as the length of time the child remained seated at
the table before leaving the room. Eating rate in grams per
minute was calculated based on the length of time from the
child’s first to last bite. Latency to eating initiation was defined
as the length of time between the child sitting at the table and
taking the first bite. The number of adult prompts to eat
delivered to an individual child per minute was defined as per
methods used in previous research.30Social interaction was
rated on a 4-point scale derived from the Mother-Child
Structured Interaction Qualitative Scales in the National
Institute of Child Health and Human Development Study of
Early Child Care, with lower scores indicating lower levels of
social interaction.31There are no definitive physiological or
behavioural indices of arousal, and as children cannot reliably
self-rate arousal level, these coded behaviours were used
instead to infer arousal level.
We first performed univariate and bivariate statistics to
evaluate differences in snack characteristics by group size, as
well as the relationship between snack characteristics and
amount eaten. We evaluated whether there was a non-linear
relationship between each of the covariates (snack duration,
latency to eating initiation, eating rate, adult prompts to eat per
minute and social interaction rating) and amount eaten by
testing the quadratic terms. Only eating rate had a non-linear
relationship with amount eaten (p=0.005 for the quadratic
term) and was therefore indexed in quartiles in the analyses
(quartile 1 (1.55 g/min, quartile 2 1.55–2.155 g/min, quartile 3
2.155–2.90 g/min and quartile 4 >2.90 g/min). To account for
repeated measures within participants and allow for missing
data, we used mixed models with random intercept to evaluate
unadjusted and adjusted differences in amount eaten by group-
size condition. We tested covariates snack duration, latency to
eating initiation, eating rate quartile, adult prompting rate and
social interaction individually in the model as potential
confounders of the relationship between group size and
consumption. An a level of 0.05 (two-tailed) was used to
determine statistical significance.
The sample included 54 children; 68% boys, 74% white, 4.2
(1.1), mean (SD) years old (range 2.6–6.2). Table 1 shows the
bivariate analyses comparing snack characteristics in small and
large groups. Table 2 shows the bivariate analyses evaluating
relationships between the snack characteristics and amount
Given the very high correlation between snack duration and
amount eaten, which is consistent with prior studies,1 26 32 33we
tested the relationship between group size and amount eaten,
controlling for snack duration. Both group size and snack
duration were significant and independent predictors of
amount eaten in this model (F(1, 52)=5.04, p=0.03 for group
size and F(1, 52)=100.33, p,0.001 for snack duration).
Controlling for snack duration, children ate slightly more when
eating in larger groups than when eating in smaller groups
(24.8 (15.9) vs 21.2 (13.4) g, p=0.03). The effect of group size,
however, differed significantly by snack duration, as evidenced
by a significant interaction term between group size and snack
duration in this model (p= 0.02). We therefore dichotomised
snack duration at the median (11.4 min) and evaluated the
relationship between group size and amount eaten in short and
long snacks. There was no effect of group size on amount eaten
in the short snacks (16.7 (11) in small groups versus 15.1 (6.6)
in large groups (F(1, 15)=0.68, p=0.42)). In contrast, in long
snacks, the amount eaten by children increased by nearly 30%
Larger group size and food consumption385
when eating in large groups compared with small groups (34.5
(16) vs 26.5 (13.8); F(1, 14)=6.83; p=0.02). We tested the
role of order of participation in each of the two conditions and
the time period between participation in each condition as
potential confounders of the relationship between group size
and amount eaten, and found neither to be significant.
Of the potential confounders tested (latency to eating
initiation, eating rate quartile, adult prompting rate and social
interaction), latency to eating initiation, eating rate quartile
and the child’s social interaction during the snack all slightly
reduced the group size effect as reflected by a reduction in the
parameter estimate for group size ranging from 18.9% to 42.2%,
and a p value for the group size effect that became just
marginally non-significant (p=0.06, 0.10 and 0.07, respec-
tively). Adult prompting rate had no impact on the relationship
between group size and amount eaten. Greater social interac-
tion was associated with less eaten (b=–4.74 (SE 2.35), p=
0.049) in the longer snacks.
This study found that for a given snack duration, children
consumed more in larger groups than in smaller groups, and
the effect strengthened as the snack time lengthened. Snack
initiation occurred more rapidly in larger groups, and eating
rate was slightly greater in larger groups than in smaller groups.
Therefore, we propose that the cumulative effective of begin-
ning to eat sooner and having a marginally greater eating rate
over time led to growing differences in the total amount
consumed over time. To our knowledge, this study is the first to
demonstrate social facilitation of quantity eaten in children.
The study also provides information about the mechanism of
the group size effect in children. Our results do not support the
time extension hypothesis. Larger group size was actually
associated with less social interaction, and there was no
difference in snack duration between the smaller and the
larger groups. The pattern of our results is better explained by
the arousal hypothesis. In the larger group, children initiated
eating more rapidly, socialised less, and ate at a slightly faster
rate than when they ate in the smaller groups.
There are several limitations to this study. Our sample size
was small, and our power may therefore have been limited to
detect more subtle effects. We did not have data on the prior
meal children consumed at home or when it was consumed,
which could have acted as a confounder. However, children’s
ability to tightly regulate intake in response to caloric preload is
limited,34 35and prior research has shown that social facilitation
easily disrupts post-prandial regulation of intake.21Finally, we
did not collect data regarding the volume of beverages that
children consumed. Nonetheless, each child was given the same
beverage in both group size conditions in which he or she
participated. The fact that beverage type was held constant
across group size conditions in the individual child would
indicate that beverage type could not act as a confounder of the
group size effect.
In summary, our study has demonstrated that when children
eat in groups of nine, they eat about 30% more than when in
groups of three for the same length of time. The effect seems to
be mediated by increased arousal. Preschool-aged children can
be included as also responding to the social facilitation effect of
group size on quantity of consumption, although the mechan-
ism of effect seems to be different from in adults, and is open to
empirical verification with physiological measures. It is not
clear from our study whether large group size increased
measures within subjects
Unadjusted means for snack characteristics by group size, accounting for repeated
Groups of 3, n=54*
Groups of 9, n=54*
sizep Value Mean (95% CI) Mean (95% CI)
Snack duration (min)
Amount eaten (g)
Eating rate (g/min)
Latency to eating initiation (min)
Adult prompts to eat per minute
Social interaction rating
13.0 (11.0 to 15.0)
21.2 (17.3 to 25.1)
2.4 (1.8 to 3.0)
3.0 (2.2 to 3.8)
0.35 (0.15 to 0.55)
3.1 (2.9 to 3.3)
12.4 (10.4 to 15.4)
24.8 (20.9 to 28.7)
2.9 (2.3 to 3.5)
1.9 (1.3 to 2.5)
0.90 (0.70 to 1.1)
2.0 (1.8 to 2.2)
*Number of observations.
characteristics and amount eaten, accounting for repeated
measures within subjects (n=108 observations)
Unadjusted relationship between snack
Slope (b; SE)r p Value
Snack duration (min)
Latency to eating initiation (min)
Adult prompts to eat per minute
Social interaction rating
Eating rate (g/min) quartile*
Quartile 2 vs 1
Quartile 3 vs 1
Quartile 4 vs 1
*Quartile 1 has the slowest eating rate.
What is already known on this topic
N Familiar behaviours increase when they occur in the
presence of others performing the same behaviour.
Adults and animals eat more when eating in the presence
of a group of others also eating, although prior work has
been limited by a lack of control of several important
N It is unknown whether social facilitation operates on
quantity of consumption in young children.
What this study adds
N Preschool-aged children eat about 30% more when
eating in a group of nine versus in a group of three.
N The results provide evidence of higher methodological
quality for the effect of group size on consumption in
humans, and raise questions about the potential relation-
ship between group eating behaviour and childhood
consumption to ‘‘supra-physiological’’ levels, or if small group Download full-text
size decreased consumption compared with ‘‘typical’’ intake.
However, given that the social facilitation effect can overwhelm
satiety mechanisms,21its potential role in contributing to
overconsumption, and thereby increasing overweight risk in
children, deserves consideration in future research.
From a clinical perspective, the results provide additional
theory-driven support for frequent recommendations given to
families regarding children’s eating behaviour. The child who
eats inadequate quantities may consume more when eating in a
group (eg, with the family at the table for a planned mealtime)
than when eating alone, as often occurs when children graze
over the course of the day. For the child who overeats,
overconsumption may be driven by having meals in over-
stimulating busy or chaotic environments, as is often the case
when eating out, particularly at fast food restaurants. Thus, the
results also support recommendations to have mealtimes at
home with the family, but for the purpose of providing a calm
and peaceful eating environment.
We thank Susana Patton, PhD, Jacinta Sitto, BA, and Tiffany Cardinal,
BS, for their thoughtful review of earlier versions of this manuscript.
We also thank Niko Kaciroti, PhD, for statistical support.
Julie C Lumeng, Katherine H Hillman, Center for Human Growth and
Development, University of Michigan, Ann Arbor, Michigan, USA
Funding: This work was supported by the American Heart Association
Fellow-to-Faculty Transition Award 0275040N to JCL. The study sponsor
had no role in study design; in the collection, analysis and interpretation of
data; in the writing of the report; or in the decision to submit the paper for
Competing interests: None.
1 Herman CP, Roth DA, Polivy J. Effects of the presence of others on food intake: a
normative interpretation. Psychol Bull 2003;129:873–86.
2 Allport FH. Social psychology. New York: Houghton Mifflon, 1924.
3 Triplett N. Thedyanmogenic factors in pacemaking and competition. Am J Psychol
4 Towler G. From zero to one hundred: coaction in a natural setting. Percept Motor
5 delaCruz BA. Laughter in children as a function of social facilitation.
Philippine J Psychol 1981;14:55–63.
6 Tolman C, Wilson G. Social feeding in domestic chicks. Anim Behav
7 Harlow HF, Yuddin HC. Social behavior of primates I. Social facilitation of
feeding in the monkey and its relation to attitudes of ascendance and submission.
J Comp Psychol 1933;16:171–85.
8 James WT. The development of social facilitation of eating in puppies. J Genet
9 Harlow HF. Social facilitation of feeding in the albino rat. J Genet Pyschol
10 Hoyenga KT, Aeschleman S. Social facilitation of eating in rats. Psychonom Sci
11 Bellisle F, Dalix AM, deCastro JM. Eating patterns in French subjects studied by
the ‘‘weekly food diary’’ method. Appetite 1999;6:41–5.
12 deCastro JM. Social facilitation of duration and size but not rate of the
spontaneous meal intake of humans. Physiol Behav 1990;47:1129–35.
13 deCastro JM. Social facilitation of the spontaneous meal size of humans occrs on
both weekdays and weekends. Physiol Behav 1991;49:1289–91.
14 deCastro JM, Brewer E. Family and friends produce greater social facilitation of
food intake than other companions. Physiol Behav 1994;56:445–55.
15 deCastro JM, et al. Culture and meal patterns: A comparison of food intake of
free-living Americans, Dutch, and French students. Nutr Res 1997;17:807–29.
16 deCastro JM, et al. Social facilitation of the spontaneous meal size of humans
occurs regardless of time, place, alcohol or snacks. Appetite 1990;15:89–101.
17 deCastro JM, Orozco S. Moderate alcohol intake and spontaneous eating
patterns of humans: evidence of unregulated supplementation. Am J Clin Nutr
18 Redd M, deCastro JM. Social facilitation of eating: effects of social instruction on
food intake. Physiol Behav 1992;52:749–54.
19 Patel KA, Schlundt DG. Impact of moods and social context on eating behavior.
20 Berry SL, Beatty WW, Klesges RC. Sensory and social influence of ice cream
consumption by males and females in a laboratory setting. Appetite
21 deCastro JM. Spontaneous meal patterns in humans: influence of the presence of
other people. Am J Clin Nutr 1989;50:237–47.
22 Clendenen VI, Herman CP, Polivy J. Social facilitation of eating among friends
and strangers. Appetite 1994;23:1–13.
23 deCastro JM, Brewer E. The amount eaten in meals by humans is a power
function of the number of people present. Physiol Behav 1992;51:121–5.
24 Klesges RC, Bartsh D, Norwood JD, et al. The effects of selected variables on the
eating behavior of adults in the natural environments. Int J Eat Disord
25 Zajonc R. Social facilitation. Science 1965;149:269–74.
26 Feunekes G, deGraaf C, vanStaveren W. Social facilitation of food intake is
mediated by meal duration. Physiol Behav 1995;58:551–8.
27 Hedley AA, Ogden CL, Johnson CJ, et al. Prevalence of overweight and obesity
among US children, adolescents, and adults, 1999–2002. JAMA
28 Peth-Pierce R. The NICHD Study of early child care. Bethesda, MD: NICHD,
29 Helburn S, Bergmann B. America’s child care problem: the way out. New York,
NY: Palgrave MacMillan, 2002.
30 Klesges RC. Parental influences on children’s eating behavior and relative
weight. J Appl Behav Anal 1983;16:371–8.
31 Anonymous. NICHD study of early child care phase I instrument document
Bethesda: National Institute of Child Health and Human Development
1991:101–3. http://secc.rti.org/instdoc.doc (accessed 26th January 2007).
32 Bell R, Pliner PL. Time to eat: the relationship between the number of people
eating and meal duration in three lunch settings. Appetite 2003;41:215–18.
33 Pliner P, Bell R, Kinchla M, et al. Time to eat? The impact of time facilitation and
social facilitation on food intake. Boston, MA: Pangborn Sensory Science
34 Birch LL, McPhee LS, Bryant JL, et al. Children’s lunch intake: effects of
midmorning snacks varying in energy density and fat content. Appetite
35 Birch LL, Johnson SL, Andresen G, et al. The variability in young children’s
energy intake. N Engl J Med 1991;324:232–5.
Larger group size and food consumption387