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Adult Weight Management

AWM: Portion Control (2006)

Citation:

Wansink B, Painter JE, North J.  Bottomless bowls:  why visual cues of portion size may influence intake.  Obes Res 2005; 13(1): 93-100.

PubMed ID: 15761167
 
Study Design:
Randomized Controlled Trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
To examine whether visual cues related to portion size can influence intake volume without altering either estimated intake or satiation.
Inclusion Criteria:
None specifically mentioned.
Exclusion Criteria:
None specifically mentioned.
Description of Study Protocol:

Recruitment

Recruited by recruiter or in response to flyer.

Design

Randomized controlled trial, between-subjects design

Blinding used (if applicable)

Not used.

Intervention (if applicable)

Subjects randomized to 2 visibility levels:  accurate visual cue of food portion (normal bowl) or biased visual cue (self-refilling bowl).  Random seating assignments.  Also completed questionnaire.

Statistical Analysis

Analyses conducted using ANOVA or Pearson correlations (with 2 tailed tests of significance).

Data Collection Summary:

Timing of Measurements

Participants required to eat soup-only lunch and complete questionnaire.

Dependent Variables

  • Intake estimation in kcal and oz, intake volume in oz, and satiety on 9-point scale on questionnaire

Independent Variables

  • Soup consumption.  Soup apparatus housed in a modified restaurant-style table in which 2 of 4 bowls slowly and imperceptibly refilled as their content were consumed. Subjects ate in groups of 4.  Actual volume determined by difference in weights.

Control Variables

 

Description of Actual Data Sample:

Initial N: 54 participants, 72% male

Attrition (final N):  54 participants

Age:  18 - 47 years, mean age 22.5 years 

Ethnicity: Not mentioned

Other relevant demographics: BMI 17.3 - 36.0 kg/m2, mean 24.9

Anthropometrics:  There were no differences between groups in terms of age, sex, BMI or retrospective measures of consumption (5.37 vs 5.43; F (1,51) = 0.016, p = 0.90). 

Location: University of Illinois

 

Summary of Results:

Other Findings

Participants who were unknowingly eating from self-refilling bowls ate more soup [14.7 +/- 8.4 vs 8.5 +/- 6.1 oz, F (1,52) = 8.99, p < 0.01] than those eating from normal soup bowls.  This difference represented an increase of 73% in amount of soup consumed and an increase of 113 kcals (267.9 vs 154.9 kcals).  Sex and BMI were not significant when included as covariates.

There were no differences between retrospective measures of consumption [5.4 vs 5.4, F(1,51) = 0.02, p = 0.90], those who had retrospectively rated themselves as hungry before the meal ate more than those who had rated themselves as less hungry.  An ANOVA using only measures of premeal hunger as covariates indicated that premeal hunger influenced consumption [F(1,50) = 5.8; p = 0.02] but showed that the effect of the cue was still significant [F (1,50) = 10.6, p < 0.01].

However, despite consuming 73% more, they did not believe they had consumed more. nor did they perceive themselves as more sated than those eating from normal bowls.  Those eating from normal bowls believed they had eaten 32.3 calories fewer than they actually ate (122.6 estimated vs 154.9 actual calories).  In contrast, those eating from self-refilling bowls believed they had eaten 140.5 calories fewer than they actually ate (127.4 estimated vs 267.9 actual calories).  

Author Conclusion:
These findings are consistent with the notion that the amount of food on a plate or bowl increases intake because it influences consumption norms and expectations and it lessens one's reliance on self-monitoring.  It seems that people use their eyes to count calories and not their stomachs.  The importance of having salient, accurate visual cues can play an important role in the prevention of unintentional overeating.
Funding Source:
University/Hospital: Julian Simon Research Chair at University of Illinois at Urbana-Champaign (internally funded)
Reviewer Comments:
Questionnaire was not tested for reliability or validity.  Normal weight subjects.
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
 
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? ???
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? No
  2.2. Were criteria applied equally to all study groups? ???
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? N/A
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? No
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? No
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) No
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.6. Were extra or unplanned treatments described? Yes
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? ???
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? ???
  7.5. Was the measurement of effect at an appropriate level of precision? ???
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes