Whether Smaller Plates Reduce Consumption Depends on Who's Serving and Who's Looking: A Meta-Analysis

Abstract

The literature on whether varying plate size has an effect on consumption is mixed and contradictory. This meta-analysis of 56 studies from 20 papers shows that varying the size of the container holding food (e.g., plate or bowl) has a substantial effect on amount self-served and/or consumed (Cohen’s d 5 .43). More generally, we found a doubling of plate size increased the amount self-served or amount consumed by 41%. Our analysis resolves the various
contradictions of past reviews: we found that the plate-size effect had a substantial effect on amount self-served (d = .51) and on amount consumed when the portion was self-served (d = .70) or manipulated along with (confounded with) plate size (d = 48). However, plate size had no effect on amount consumed when the portion size was held constant (d = .03). Overall, plate size had a stronger effect when participants were unaware that they were participating in a food study (d = .76).

Full text

THE BEHAVIORAL SCIENCE OF EATING
Whether Smaller Plates Reduce Consumption
Depends on Who’s Serving and Who’s Looking:
A Meta-Analysis
STEPHEN S. HOLDEN, NATALINA ZLATEVSKA, AND CHRIS DUBELAAR
ABSTRACT The literature on whether varying plate size has an effect on consumption is mixed and contradictory.
This meta-analysis of 56 studies from 20 papers shows that varying the size of the container holding food (e.g., plate or
bowl) has a substantial effect on amount self-served and/or consumed (Cohen’sd5.43). More generally, we found a
doubling of plate size increased the amount self-served or amount consumed by 41%. Our analysis resolves the various
contradictions of past reviews: we found that the plate-size effect had a substantial effect on amount self-served (d5
.51) and on amount consumed when the portion was self-served (d5.70) or manipulated along with (confounded
with) plate size (d548). However, plate size had no effect on amount consumed when the portion size was held con-
stant (d5.03). Overall, plate size had a stronger effect when participants were unaware that they were participating
in a food study (d5.76).
Does plate size affect how much we eat? The Small
Plate Movement (www.smallplatemovement.org) is
founded on the premise that smaller plates lead us
to eat less, but the evidence on the effect of plate size
1
is greatly disputed. Some researchers report that smaller
plates reduce consumption (Wansink and Kim 2005; Wan-
sink, Payne, and Werle 2008; Van Kleef et al. 2012; Wansink
and Van Ittersum 2013). But many others report finding
no effect (Rolls et al. 2004, 2007; Shah et al. 2011; Yip et al.
2013; Libotte et al. 2014). Some even report negative effects
(e.g., Robinson et al. 2015c).
Four recent reviews do little to clarify the effects of plate
(or bowl or other food-container) size on consumption. In
a qualitative review, Casazza et al. (2015) concluded that
plate size was a “robust driver of self-served portion sizes.”
Robinson and Matheson (2015) in another qualitative re-
view concluded that “smaller diameter plates [and] bowls”
reduce consumption while acknowledging that there were
some studies that showed no effect. In the only meta-
analysis (quantitative review), Robinson et al. (2014b) con-
cluded that “evidence to date does not show that dishware
size has a consistent effect on food intake.”Finally, Libotte
et al. (2014) in another qualitative review noted that de-
spite widespread recommendations to use plate size to con-
trol portions, “the evidence to supportthis is contradictory.”
In short, the effects of plate size are unclear. We there-
fore sought to answer the question of whether smaller plates
reduce consumption and, given the equivocal results, to de-
termine the conditions under which plate size affects con-
sumption.
We first distinguished between two distinct dependent
variables: the amount of food self-served vs the amount con-
sumed. Robinson et al.’s (2014b) meta-analysis focused on
“formally measured or recorded food intake,”while Casazza
et al. (2015) focused on self-served portions. In general,the
amount self-served is presumed to mediate the amount con-
sumed (see fig. 1), an assumption confirmed in a number of
studies that examine both dependent variables (e.g., Koh
and Pliner 2009; Van Kleef et al. 2012). Wansink and Johnson
(2015) and Robinson et al. (2015b) report that studies mea-
suring both show that the amount consumed is 85%–90%
of the amount self-served. However, the effect of plate size
on amount consumed might be different if portions are not
self-served. We therefore examined both dependent variables.
In terms of independent variables, we first distinguished
between manipulations of area (i.e., plate size in its strict
Stephen S. Holden is honorary associate professor of marketing at the Macquarie Graduate School of Management, Macquarie University, Australia.
Natalina Zlatevska (nzlatevs@bond.edu.au) is senior lecturer, marketing, at University of Technology Sydney, Australia. Chris Dubelaar is professor of mar-
keting and associate dean, research and development, at Deakin University, Australia.
1. We are using the term “plate size”generically here. It therefore includes plates, bowls, and other food containers such as packages.
JACR, volume 1, number 1. Published online January 1, 2016. http://dx.doi.org/10.1086/684441
©2016 the Association for Consumer Research. All rights reserved. 2378-1815/2016/0101-0013$10.00

sense) and volume (as in bowls and packages). Some studies
manipulate the plate size in two dimensions (i.e., expand-
ing the diameter of a round plate increases its area); others
manipulate three dimensions (i.e., increasing the volume).
Importantly, both Robinson et al. (2014b) and Libotte et al.
(2014) have observed that manipulations of area appeared
to have no effect, while manipulations of volume did. This
result seems surprising as a doubling of area would be more
noticeable than a doubling of volume. Research by Chan-
don and Ordabeyeva (2009) and Ordabeyeva and Chandon
2013) supports this notion by showing that consumers ap-
pear to be more sensitive to a manipulation in one dimension
and less sensitive to manipulations in three dimensions. We
therefore sought to reexamine this unexpected result.
We also distinguish between whether it was the consump-
tion plate or the serving plate that was manipulated, a vari-
able Libotte et al. (2014) referred to as “food-serving mode.”
Conceptually, consumption and serving plates could inde-
pendently and even interactively affect both amount of
food self-served and amount consumed (see fig. 1). Whilecon-
sumption and serving-plate manipulations could be crossed,
no one has done so to our knowledge. We anticipated that
manipulations of the serving-plate size and the consumption-
plate size would show a positive effect.
We also examined two further variables that have been
little examined in the past. The first is to break down those
studies examining amount consumed by how the portion
size was manipulated: was the portion size fixed (the same
for both plate sizes), self-served, or varied (and therefore
confounded) with plate size. Research has shown that por-
tion size has a strong effect on consumption (doubling of a
portion leads to 35% greater consumption on average; Zla-
tevska et al. 2014). We therefore sought to examine whether
plate size had an effect independent of portion size.
The second is whether the plate-size effect is mitigated
in studies where people are aware that they are participat-
ing in a food study. A number of recent studies suggest that
awareness may mitigate various food consumption effects in
general (Robinson et al. 2014a) and, more specifically, plate-
size effects (Libotte et al. 2014), portion-size effects (Zla-
tevska et al. 2014), and partitioning effects (Holden and Zla-
tevska 2015).
Finally, we also extended previous analyses by address-
ing the multidimensionality and scalability of plate size by
developing an elasticity measure of the effect of plate size
on consumption.
METHOD
We have followed PRISMA principles (Preferred Reporting
Items for Systematic Reviews and Meta-Analyses) as the ba-
sis for reporting our method and our results (Beller et al.
2013). The interventions we examined were manipulations
of plate size (defined broadly as plate, bowl, and other food
container); the outcomes we examined were amount self-
served and amount consumed. Further details on the inter-
ventions, outcomes, and studies that were included in our
analysis are provided in the following.
Interventions
Our primary interest was in examining the effect of plate-
size manipulations, so studies needed to have at least two
levels of plate size to be included in the analysis.
2
Some stud-
ies included three or more levels, for example, “small,”“me-
dium,”and “large”(Rolls et al. 2004, 2007). In these cases, the
comparison of “small”versus “medium”was entered into the
meta-analysis as one study and “medium”vs. “large”as an-
other. We note that Robinson et al. (2014b) did this but also
included an additional study comparing “small”versus “large.”
We did not because it creates a problem of “double-counting”
the effects. It also creates one effect that is a function of a ma-
nipulation that is equal to the sum of two other manipula-
tions. This highlights that the plate size effect is scalable,
and we might expect a larger change from a larger change
in plate size. This is an issue that we address later.
In order to try and separate some of the conflicting find-
ings regarding plate size, we distinguish between various types
of interventions. First, and in line with Robinson et al. (2014b),
we distinguish between manipulation of area whether re-
ported as diameter (e.g., Rolls et al. 2007) or area (e.g., Koh
Figure 1. Plate size effects.
2. We excluded studies that manipulated the size and number of con-
tainers simultaneously. Specifically, Wansink and Cheney (2005), which
manipulated both the size and the number of serving bowls (2 #4L
vs. 4 #2 L), was excluded even though it was included in other reviews
(Libotte et al. 2014; Robinson and Matheson 2015). The problem is that
the size manipulation is confounded with the number manipulation, a fea-
ture of “partitioning”studies that can have paradoxical and contradictory
effects (Zlatevska et al. 2014; Holden and Zlatevska 2015).
Volume 1 Number 1 2016 135

and Pliner 2009), and also volume whether reported as bowl
size (Ahn et al. 2010) or package size (Wansink and Kim
2005). Second and in line with an observation by Libotte
et al. (2014), we distinguished between whether the plate
being manipulated was the serving plate (e.g., Wansink
1996) or the consumption plate (e.g., Rolls et al. 2007).
Outcomes
Amount of food consumed was recorded in a wide variety
of ways: grams (Marchiori et al. 2012), ounces (Wansink
et al. 2006), kilojoules (Shah et al. 2011), calories (Di Santis
et al. 2013), and “percentage of plate surface”(Wansink and
Van Ittersum 2013). To avoid any confusion with energy in-
take (kilojoules), we only included amount consumed for
foods that were homogenous in terms of energy density. In
such cases, whether a study measured weight consumed or
energy consumed was of no consequence.
3
We also included studies that reported amount self-served
even though they were excluded in some previous reviews.
4
We note that five studies measured both amount self-served
and amount consumed and are therefore reported for each
outcome (Koh and Pliner 2009; Van Kleef et al. 2012; Di
Santis et al. 2013; Van Ittersum and Wansink 2013; Wansink
et al. 2014).
We excluded all studies that measured perceptions and
judgments such as serving a portion to match a target
(Bryant and Dundes 2005; Van Ittersum and Wansink
2012; McClain et al. 2014; Penaforte et al. 2014). Despite
their promise, we also excluded studies that measured body
weight change (Pedersen et al. 2007; Ahn et al. 2010; Hanks
et al. 2013)
5
and food waste (Kallbekken and Sælen 2013) as
the outcomes.
Participants and Study Designs
We included both within-subject (e.g., Rolls et al. 2007) and
between-subject experimental designs (e.g., Wansink and
Van Ittersum 2013), field and laboratory based experiments,
with both random (e.g., Van Kleef et al. 2012), and non-
random assignment of subjects to conditions (e.g., Koh and
Pliner 2009).
Search Strategy
Studies relevant for the meta-analysis were initially identi-
fied through a search of ABI/Inform, ProQuest Digital Dis-
sertations, Business Source Premier, Web of Science, Psych-
Info, SCOPUS, Google Scholar, and other databases using
the following keywords: portion size, plate size, package size,
bowl size, dishware, and container size. We also manually
searched through the following relevant journals and con-
ference proceedings where papers on portion size, plate size,
or container size have been previously published: Journal
of Marketing,Journal of Marketing Research,Journal of Con-
sumer Research,Journal of Consumer Psychology,Journal of
Public Policy and Marketing,Obesity Reviews,Annual Review
of Nutrition,American Journal of Clinical Nutrition,Body
and Society,British Journal of Sociology,Social Science and
Medicine,Appetite,Journal of Obesity Research,Advances in
Consumer Research, American Marketing Association pro-
ceedings, and the Obesity Society abstract supplements.
The references in articles found in our search were also ex-
amined to identify further studies. We also acknowledge
and thank the reviewers and editors for identifying some
articles that were in press or otherwise missed through the
above process.
Data Extraction
We recorded data from each study that would allow for the
calculation of a standardized mean difference (Cohen’sd; see
figs. 2a,2b). To enable the later calculation of an elasticity
coefficient, we also recorded the amount self-served and/
or consumed from the “small”and “large”plate size condi-
tion and the size of the plate if, and as, reported by the re-
searchers themselves.
Finally, we coded for two further variables of interest.
First, we coded for whether or not portion size was self-
served, manipulated along with (i.e., confounded with) plate
size, or held constant across plate-size conditions. Second,
we coded for whether people were aware that they were
participating in a “food study.”For participants to be un-
aware, the research would generally feature a nonfood cover
story, and consumption was measured covertly. While it is
difficult for a within-subjects design to disguise the fact that
food is the focus of the study as noted by Van Kleef et al.
(2012), within-subject designs with children were, in some
instances, included (e.g., Van Ittersum and Wansink 2013;
Wansink et al. 2014, study 2). These studies featured a
3. Studies measuring the consumption of nonfood items such as
bleach and detergent were excluded (Wansink 1996, study 5). A six-week
pilot study showing a decline in consumption by Robinson and Matheson
(2015) also had to be excluded due to insufficient data.
4. We note that while some previous reviewers focused on amount
consumed (Libotte et al. 2014; Robinson et al. 2014b), they did appear
to include some studies measuring amount self-served (e.g., Wansink
et al. 2006; Van Ittersum and Wansink 2013).
5. Ahn et al.’s (2010) data on actual consumption were included.
136 Smaller Plates Reduce Consumption Holden, Zlatevska, and Dubelaar

field-setting such as a school or summer-camp, and the food
manipulations were incorporated into regular meals with-
out notice to the children, so we judged the participants
were unaware.
RESULTS
Fifty-six studies reported in 20 papers representing over
3,507 subjects were included in our meta-analysis (see figs.
2a,2b; for details of the included studies and their respec-
tive effect-sizes; see appendix, available online, for full de-
tails of all studies). Using Cohen’sd, a measure of standard-
ized mean differences, calculated under a random effects
model, we found the overall effect of plate size across the
56 studies was d5.43 (95% confidence intervals ±.11),
which would be described conventionally as a medium
effect-size (Cohen 1988).
To address the file-drawer problem (Rosenthal 1979),
we calculated the fail-safe N to be 2,828. This is “the num-
Figure 2a. Effect of plate size on amount consumed.
Volume 1 Number 1 2016 137

ber of [null effect] studies that would need to be added
to a meta-analysis to reduce an overall statistically signifi-
cant observed result to non-significance”(Rosenberg 2005,
464). A visual observation of the funnel plot for the k5
56 studies shows some asymmetry with some studies with
larger standard errors being overrepresented. The first pos-
sible interpretation is that this shows publication bias. How-
ever, another possibility is that given the scalability of plate
size, the variation in standard errors may represent differ-
ent strength manipulations of plate size (Sterne et al. 2011).
That a large change in plate size might result in a larger ef-
fectis something we will capture later by calculating the plate
size elasticity of consumption. In any case, standard meta-
analytic reporting gives less weight to studies with higher
standard errors and smaller n’s.
The heterogeneity of studies was considerable and the
effect-size varied from study to study as indicated by Q 5
212.3, which was much greater than the degrees of free-
dom (df 555). The I
2
index, indicating the percentage of
variation in the meta-analysis that was attributable to study
Figure 2b. Effect of plate size on amount self-served.
138 Smaller Plates Reduce Consumption Holden, Zlatevska, and Dubelaar

heterogeneity, was a substantial 74% (Higgins and Thomp-
son 2002; Huedo-Medina et al. 2006).
The overall d5.43 shows that plate size had a positive
effect on amount consumed and/or self-served. Due to the
high degree of study heterogeneity, the fact that five stud-
ies provided measures of both amount self-served and
amount consumed (and are therefore double-counted), and
the existence of reviews reporting no plate size effect at least
in terms of those studies which manipulate only area as op-
posed to volume (Libotte et al. 2014; Robinson et al. 2014b),
we proceeded by breaking down the effect.
We first examined plate size effects broken down by
the outcome measured (amount consumed vs. amount self-
served), dimensions manipulated (area vs. volume), and
type of plate (consumption vs. serving plate; see fig. 3). This
analysis enabled us to understand more clearly the con-
flicting views of whether plate size has an effect, but we
caution against interpreting this analysis as if the variables
are fully crossed in an experimental sense. As may be seen,
some cells in this analysis had no or few observations: we
found no studies manipulating the area of a serving plate,
and only one study that examined the effect of a volume
manipulation on amount consumed (Van Kleef et al. 2012).
Even for those cells with more observations, the studies
contained in each cell differed from studies in other cells
in many ways beyond those variables used to create the
subgroups.
As shown in figure 3, plate sizes had moderate to strong
effects on amounts self-served and consumed across most
cells (d5.33 up to d51.15). There was one notable excep-
tion: the manipulation of area of consumption plates had a
small (and nonsignificant) effect on amount consumed (d
A
5
.06 ±.20). This single cell where the area of a consumption
plate was manipulated appears to account for the conflicting
conclusions seen in the literature. The two reviews which fo-
cused on amounts consumed (top half of fig. 3) concluded
that manipulations of area (“plates”) had no effect relative
to manipulations of volume (“bowls”; Libotte et al. 2014;
Robinson et al. 2014b). However, our analyses show that area
and volume had an approximately equal effect on amount
self-served (d
area
5.49 ±.30 vs. d
volume
5.52 ±.19) (bottom half
of fig. 3). The two other reviews focused on amount self-
Figure 3. Effects of plate size: summary.
Volume 1 Number 1 2016 139

served and accordingly concluded that plate size had a clear
positive effect (Casazza et al. 2015; Robinson and Matheson
2015).
While the presentation in figure 3 may encourage us to
think that the anomalous effect is driven by something spe-
cial about the interaction of area and consumption plate,
we again highlight that it would be a mistake to think of
the elements in this cell as having been randomly drawn
from the population of all possible studies. This is perhaps
highlighted by the fact that five of the 10 studies in this cell
are from one article (Rolls et al 2007), and that there are
no observations of the effect of manipulating the serving-
plate area on amount consumed.
We then proceeded by examining theindependent effects
of five different variables on the plate size effect: (1) out-
come variable (amount consumed vs amount self-served),
(2) dimensions manipulated (area or volume), (3) type of
plate (consumption vs serving), (4) whether subjects were
aware that they were participating in a food study or not,
and (5) how portion size was manipulated within plate size
for amount consumed. The results are presented in figure 4.
Of the five variables examined, the effect of plate size
remains fairly consistent whether amount is self-served or
amount consumed is measured, and whether area or vol-
ume, and serving plate or consumption plate is manipulated.
However, the effect of plate size is considerably greater un-
der specific conditions as shown in the bottom two panels
of figure 4. Specifically, the plate-size effect was greater
when consumers were unaware that they were participating
in a food study (d
unaware
5.76 vs d
aware
5.31). We note that
Figure 4. Effects of plate size: analysis by subgroups. * This analysis examines the effect of plate size on amount consumed only (k527).
140 Smaller Plates Reduce Consumption Holden, Zlatevska, and Dubelaar

not only was the effect larger, but it was statistically signif-
icant—the 95% confidence intervals for each estimate do
not overlap. Furthermore, examining the effect of plate size
on amount consumed, the effect was stronger if the consum-
ers self-served their portions, or the portion sizes were con-
founded with the plate size. There is an important implica-
tion here—plate size does not appear to have an effect on
amount consumed if the portion size remains fixed across
plate sizes. So while the effect of plate size on amount con-
sumed and amount self-served does not appear to be very
different on average, the results suggest that the effect of
plate size on amount consumed is, to a large degree, me-
diated by a portion-size effect. In the case of self-service,
the larger plates apparently encourage larger portions, and
so the consumer eats more.
We note that there are insufficient observations to say
whether the effect of unawareness is crossed with these other
variables. Of the 10 studies in which portion size was fixed,
all comprised participants who were aware they were partic-
ipating in a food study. Further research is required to estab-
lish whether or not plate size might have an effect where the
portion is fixed if participants are unaware.
A limitation of this subgroup analysis is that it ignores
possible interactions of the identified variables with one an-
other, although, as noted, the lack of observations and lack
of random sampling constrain any effort to conduct such
an analysis. However, the problem does highlight that the
anomalous cell seen in figure 3 where the plate size effect
has no effect, may reflect the influence of variables other
than those identified. For instance, in this anomalous cell,
nine of the 10 studies were with subjects who were aware
they were participating in a food, which tends to show a
smaller effect as seen in figure 4. Moreover, there was one
study out of 10 in this cell that showed a strong plate-size
effect (Wansink and Van Ittersum 2013, study 2; see fig. 2a).
The subjects in this study self-served their portions and were
unaware they were participating in a food study.
Scaled Effect Size
To complete our analysis, we developed a scalable measure
of the plate size effect to address the problem that Cohen’s
dis difficult to interpret. Cohen’sd(and related standard-
ized mean difference measures) report the effect of “con-
trol”versus “treatment”or, in our case, large versus small
plate size, but nothing beyond this (Chernev et al. 2010).
No allowance is made for the fact that some researchers in-
creased the plate size from the small to large condition by
200% (Marchiori et al. 2012), while others increased it by
just 30% (Rolls et al. 2004). In other words, effect size as
measured by Cohen’sdcannot capture a plate-size effect
that changes as a function of the change in plate size.
In an effort to address this problem, we calculated per-
centage change in plate size and the resulting percentage
change in consumption to allow for the effect-size to be ex-
pressed as a plate size elasticity of consumption. The per-
centage change in consumption was calculated as follows:
DC=CS;(1)
where DC5change in consumption (amount eaten from
larger plate 2amount eaten from smaller plate) and CS 5
consumption from smaller plate size.
We then calculated the same change parameter for plate
size, although we note that it was necessarily conditioned
on the dimensions that were manipulated. For those stud-
ies reporting plate size as a diameter, we first converted
this into an area ((diam/2)^2*p) and then expressed change
in area for all observations as follows:
DA=AS;(2)
where DA5change in area (larger area 2smaller area) and
AS 5smaller area.
Change in volume was measured in a similar way al-
though we note that studies typically report change by ca-
pacity of the container (e.g., 100-g package or 2-L bowl) and
almost never included information about the actual physi-
cal dimensions:
DV=VS;(3)
where DV5change in volume (larger volume 2smaller
volume) and VS 5smaller volume.
We then regressed change in consumption (eq. [1]) on
the change in plate size (be it area as in eq. [2] or volume
as in eq. [3]) with no constant and with each study weighted
by the meta-analytic weights generated under a random ef-
fects model.
6
The coefficient generated represents an elas-
ticity measure which can be interpreted as the percentage
change in consumption for a doubling (100%) increase in
plate size.
6. The regressions were modeled without a constant because a zero
percent change in plate size has a zero percent change in consumption.
In any case, and following Eisenhauer (2003), we note that when included,
the constant was not significant, and the coefficient for change in plate
size was little changed. While the presented regressions were weighted,
unweighted regressions returned virtually identical results, consistent with
the random-effects model weights being more “balanced”than under fixed-
effects (Borenstein et al. 2009).
Volume 1 Number 1 2016 141

Looking across all 56 studies combined (including five
studies that provided measures of both amounts self-served
and consumed), doubling the plate size led to increases in
amounts self-served/consumed of 41% on average ( p<.001,
k556). Alternatively stated, halving the plate size led to a
29% reduction in amount self-served/consumed on average.
This scalable measure might offer some promise for explor-
ing the conditions under which plate size effect varies but
requires more observations (studies) in order to be stable.
DISCUSSION
The results from both the meta-analysis and the elasticity
analysis show that plate size has a considerable effect over-
all on amount self-served and consumed. While two previ-
ous reviews concluded that plate size had no reliable effect
on amount consumed (Libotte et al. 2014; Robinson et al.
2014b), our analysis found that there was a substantial
plate size effect on amount consumed, but only if the con-
sumer self-served their portions or portion size was varied
in line with plate-size. Plate size had no effect on average in
situations where portion sizes were held constant across
plate sizes.
Our analyses have also suggested that a major driver of
the effect is whether subjects are aware that they are par-
ticipating in a food study or not. If participants were un-
aware that they were participating in a food study, the effect
of manipulating plate-size was substantially (and signif-
icantly) larger (d
unaware
5.76 vs. d
aware
5.31), a finding in line
with a suggestion by Libotte et al. (2014). This result is
consistent with other recent reports suggesting that im-
portant demand effects operate in food studies. Zlatevska
and colleagues (Zlatevska et al. 2014; Holden and Zlatevska
2015) have showed that the effects of portions and parti-
tions respectively were reduced when research participants
were participating in a study where food was the focus. Rob-
inson and colleagues (Robinson 2014; Robinson et al. 2014a,
2015a) have conducted a meta-analysis and empirical stud-
ies showing that when subjects know they are being ob-
served, their consumption is reduced.
Overall, our analysis supports the notion that plate size
positively influences consumption when portions are self-
served or varied in line with plate size and if consumers
are unaware that their consumption is being monitored.
But significant areas remain to be explored more fully. Our
research highlights that more attention needs to be directed
to the distinction between amount consumed and amount
self-served and, in particular, the way in which self-served por-
tions may effectively mediate the observed plate-size effect.
While some previous reviewers have suggested that bowls
or manipulations of volume have a greater effect than ma-
nipulation of area (Libotte et al. 2014; Robinson et al. 2014),
we consider this unlikely. Our results show that there is little
distinction between manipulating a plate in two dimensions
(area) or three dimensions (volume as in a bowl). More-
over, if there were to be a difference, we would expect two-
dimensional changes to have a greater effect than three-
dimensional changes in view of the compelling evidence that
the perceived size and perceived change in size in containers
is quite distinct from the actual change (Chandon and Orda-
bayeva 2009; Ordabayeva and Chandon 2013). Changes in one
dimension are generally perceived as bigger than an equiv-
alent change in three dimensions (Raghubir and Krishna
1999; Chandon and Ordabayeva 2009). In any case, very
few of the studies included in our analysis gave any consid-
eration to the perceived change. With regard to volume in
particular, we found virtually no studies that reported the
dimensions of the container. This made it impossible to
code those studies manipulating volume for the number
of dimensions changed. Given the promising opportunities
offered through the manipulation of one versus all three
dimensions as highlighted by Chandon and Ordabeyeva
(2009), we think that it would be helpful if, at the very least,
future studies examining the effect of plate size, and espe-
cially volume, report the three dimensions of the container
of both the smaller and larger plate.
In terms of future directions and implications, we think
that further exploration of the awareness by participants
of their participation in a food study deserves more atten-
tion. In their qualitative review, Libotte et al. (2014) noted
that in all the studies they reviewed where they found a
plate-size effect, “participants were distracted from food-
consumption or serving,”and “no distraction factors were
present in the studies that did not find a significant effect
of plate size.”They confirmed this in their own study of
plate size in a setting using a “fake-food buffet”: their study
produced no effect. In our review, we report no effect of
plate size on amount consumed if the portion size was held
constant but there is an important caveat: all studies con-
tributing to this result featured participants who were aware
they were in a food study. Therefore, we need studies with
unaware participants investigating whether or not plate size
has an effect when portion sizes are held constant.
In view of the potential importance of subject aware-
ness, we add our voice to Robinson’s (2014) call “to lie more
to participants in eating behaviour experiments.”Impor-
tantly, we highlight that the blinding required is more than
142 Smaller Plates Reduce Consumption Holden, Zlatevska, and Dubelaar

simply blinding to the manipulation but also blinding to the
measurement. That is, the individual needs to be “double-
blinded”: unaware of the plate size manipulation and un-
aware even that they are participating in a food-consumption
experiment.
However, we also hasten to add that blinding in the clas-
sic social experimentation sense overlooks another prom-
ising possibility related to the human adaptation to novel
stimuli (Berlyne 1971). A novel stimulus attracts attention
initially, becomes familiar, and ultimately is forgotten. This
may explain how some longer-term trials with smaller dish-
ware have reported success in reducing consumption (Ahn
et al. 2010; Robinson and Matheson 2015) and weight
(Pedersen et al. 2007; Hanks et al. 2013). Ensuring partic-
ipants are blind to the manipulation or the measurement in
such trials is likely to be virtually impossible. We speculate
that awareness of the changed dishware attenuates over
time. The result is therefore consistent with the notion
that the effect works best when the participant is blind
to the intervention. The difference is that through adapta-
tion, the consumer becomes blind to long-term manipula-
tions of plate size.
In summary, smaller plates will reduce the amount self-
served to a plate. Smaller plates also reduce the amount
consumed if the consumers are self-serving to those smaller
plates or portion size is manipulated in line with the plate
size. However, simply reducing plate size and holding por-
tion size constant appears to have no effect—but this needs
further investigation with unaware consumers. The plate-
size effect is observed to be larger if the consumers do not
believe they are being watched. So the widespread, long-
term use of smaller plate sizes may help reduce consump-
tion and perhaps obesity in precisely the same way that we
have become blind to how large plate sizes have become. Con-
tinual use of smaller plate sizes may be both habit-forming
and good for your health.
THE LARGER THEME: SMALL STEPS
TOWARD OVERCOMING OBESITY
Obesity is growing (Flegal et al. 2002, 1998; Young and
Nestle 2002), and concern about obesity is growing at a pro-
portional rate. Despite enormous amounts of research and
attention directed to the obesity problem, there appear to
be no simple solutions. Perhaps this is an important find-
ing: there is no large simple solution; rather obesity can
only be successfully tackled by a series of small steps.
Our research suggests that substituting small for larger
plates is one such small step that will help, especially if con-
sumers are self-serving to the plate, and if the change to
smaller plates is not signaled to the consumer. This research
fits within a larger field of small ways in which the amount
we consume can be potentially limited by portions served
such as smaller plates (shown in this article), smaller “food
units”(Davis et al. 2016), smaller portions (Zlatevska et al
2014), partitioned portions (Holden and Zlatevska 2015),
or conversely, encouraging people to eat less by making por-
tions appear larger (e.g., Wansink and Van Ittersum 2003,
2006; McClain et al. 2014).
At a broader level, the efforts toward downsizing con-
sumed portion sizes all fit within a much larger field of small
steps used to modify the consumption environment so as to
nudge people toward healthier and less wasteful consump-
tion behaviors (e.g., Szocs and Biswas 2016; Williamson,
Block, and Keller 2016).
So there are solutions: they are small but also numerous.
The greatest challenge perhaps is how to implement these
ideas. In this regard, we see four different stakeholders we
need to address: public health policy makers, food market-
ers, consumers, and food researchers.
The first stage in encouraging these small steps toward
a solution is through the public health policy path. But it is
difficult to imagine how these small steps might be imple-
mented by the public health authorities, especially given evi-
dence that consumers can react negatively to heavy-handed
approaches (Pham et al. 2016). The best public health ap-
proach would appear to be to provide information and ideas
for implementing small changes and leaving the changing to
others.
A second step is for marketers to actively engage in en-
couraging healthier consumer habits. While some may view
marketer involvement with some caution, they do in fact
have the capacity—and in many instances, the interest—
to help nudge consumers in the right direction. In this regard
then, we might encourage marketers to implement ideas
such as making healthy the default option (e.g., Peters et al.
2016).
Ultimately, change has to be implemented at the consumer
level, and for this to work, a more consumer-empowered,
bottom-up approach is probably needed. In this consumer-
centric version, consumers are encouraged (by distributed
information) to make informed decisions to help them-
selves. It is noted that in this regard, the very public outcry
about the growth in obesity may be viewed as a positive. Due
to this media attention, many consumers are searching for
solutions, even if small and subtle. The Small Plate Move-
ment (www.smallplatemovement.org) is an excellent exam-
Volume 1 Number 1 2016 143

ple of a consumer-focused intervention that encourages bet-
ter habits for better living.
Finally, food researchers can help, and our research sug-
gests directions for future efforts. While food researchers
are typically united in seeking solutions for obesity, a search
for strong, simple solutions can potentially hide smaller,
subtle solutions. Our research was motivated by the con-
siderable confusion about whether small plates work to re-
duce consumption. Many had studied the effect of small
plate sizes in various settings, which generated a wide range
of results, positive, neutral, and even negative. Even review
articles have disagreed about whether there is an effect
or not (Libotte et al. 2014; Robinson et al. 2014b; Casazza
et al. 2015; Robinson and Matheson 2015). Our research
resolved this confusion: we show that the effect of smaller
plates on amount self-served is substantial, but the effect
of smaller plates on amount consumed holds only under
specific conditions, notably where consumers self-serve
their portions or when portion size is reduced along with
plate size. More research on the small steps that can be taken,
and the conditions under which they do and do not oper-
ate, is to be encouraged.
Our research also revealed another sometimes entrenched
practice in food science that we believe needs shifting: we
found the overall effect of plate sizes was stronger if study
participants were unaware that their consumption is being
monitored. Our article adds to a growing body of research
suggesting that the effects of portion sizes and partitioning
are mitigated when subjects are aware they are in a food
study (Zlatevska et al. 2014; Holden and Zlatevska 2015).
This fits with broader reviews showing that aware partici-
pants tend to modify or constrain their consumption (Rob-
inson et al. 2014a, 2015a). Importantly then, the small and
subtle steps that can be used to modify consumption might
be missed in studies where participants are aware they are
in a food study.
The obesity problem can be resolved—through a series
of small steps. Our research offers some clarification around
one such small step. Use small plates, especially if you are
self-serving your food to your plate. It will encourage you
to self-serve and eat less. What about the problem that if
someone installs smaller plates in their household, every-
one will know, that is, be aware of the change? Our research
does show that smaller plates work best if people are un-
aware that their consumption is being monitored. Fortu-
nately, while humans tend to notice novel stimuli, the flip
side is that they tend to adapt to and overlook familiar
stimuli. So even if the change to small plates in a household
is a conscious decision, over time, the members of the house-
hold are likely to become unaware of the change, and we
might expect to see behavior change accordingly. There is
already some evidence to suggest that this is the case with
individuals adopting smaller dishware showing a loss of
weight over time (Pedersen et al. 2007; Hanks et al. 2013).
The problem of obesity is growing. Smaller plates are one
of a range of small steps that can help reduce the amount
self-served and thus the amount consumed.
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