Abstract
An increase in the portion size leads to an increase in energy intake, a phenomenon
which is also referred to as the portion size effect. Previous research has shown that this
effect occurs for different kinds of people, in different settings, and for different foods.
Furthermore, the portion size effect persists over longer periods of time and has therefore
been connected to the worldwide increase in overweight and obesity. Portion and pack sizes
have increased in recent years and it is thus important to find ways to prevent the occurrence
of the portion size effect.
In Chapter 2 I review what is known about the portion size effect to date and discuss
possible causes of the effect. I expand on the view that consumers are uncertain about how
much they should eat and therefore rely on external reference points, such as the portion
size, to determine their consumption amount. The way the portion size is incorporated in the
consumption quantity decision can vary, which leads to four different explanations for the
portion size effect: cleaning the plate, unit bias, anchoring, and portion sizes as social norms.
To prevent the portion size effect, people can be encouraged either to rely less on external
reference points or to use other external reference points in the consumption decision.
In Chapter 3, we tested whether the portion size acts as a social norm and as such
communicates how much is appropriate to eat. In two online experiments, we manipulated
the normative relevance of the portion size, either by providing information that the portion
size communicated the behaviours of an in-group (own university students) or out-group
(students from a different university), or that it was approved by a minority or majority of a
relevant social group. Results showed that participants expected to eat and serve more from
larger than from smaller portions, but that this portion size effect was less pronounced when
the normative relevance of the portion size was decreased. Furthermore, in Experiment 3.2,
the relation between portion size and the expected amount served was partly mediated by
the amount that was considered appropriate, providing further evidence that the portion size
is indeed an indicator of the appropriate amount to eat. At the same time, mediation was only
partial, and although the normative relevance manipulation weakened the portion size effect,
it did not prevent it. Hence, social concerns about eating appropriately certainly play a role
in the portion size effect, but there seem to be other causes as well.
In Chapter 4, we focussed on preventing the portion size effect by motivating people
not to use external reference points, such as the portion size, in their consumption quantity
decision. Previous research has shown that providing diet-concerned individuals with a
reminder of their dieting goal can help them control their consumption, and we investigated
whether such a reminder would also be effective in reducing the pack size effect. In
Experiment 4.1, expected consumption of a number of snack foods was measured, and a
dieting magazine served as the diet prime. In Experiment 4.2, actual consumption of M&M’s
was measured, and dieting commercials served as diet primes. The results of both
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experiments indeed showed that restrained eaters lowered their (expected) consumption
from large snack packages when exposed to a diet prime and as a result the pack size effect
disappeared.
In Chapter 5, we tested whether instead of motivating people not to use an external
reference point in the consumption decision, it might be effective to provide people with an
alternative, better reference point in the form of a serving size recommendation. In three
experiments, we measured (expected) consumption of unhealthy snack foods which were
provided in either a small or large package which did or did not contain the serving size
recommendation. Furthermore, we tested both a pictorial serving size recommendation,
which displayed food amounts visually and a non-pictorial recommendation, which
communicated the recommended amount in grams only. Only the pictorial recommendation
reduced (expected) consumption from large packs and hence weakened the pack size effect.
Although the serving size recommendation reduced the pack size effect, it did not seem to
fully remove it, suggesting that it might not have provided sufficient motivation for everyone
to no longer incorporate the portion size in the consumption quantity decision.
In summary, it is difficult, but not impossible to weaken the portion and pack size effect.
These findings also imply that the tendency to eat more when more food is provided, is to a
certain extent under conscious control. This means, that with sufficient help, people will be
able to rely less on environmental cues, such as the portion size, when making consumption
decisions.
Original language | English |
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Awarding Institution |
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Supervisors/Advisors |
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Award date | 21 Apr 2016 |
Place of Publication | Rotterdam |
Print ISBNs | 9789058924384 |
Publication status | Published - 21 Apr 2016 |
Research programs
- ESE - MKT
- RSM MKT