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AWM: Portion Control (2006)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To investigate the effect on energy intake of increasing the portion size of a food served as a discrete unit.

Inclusion Criteria:

Healthy nonsmoking individuals aged 20 - 45 years, with reported BMI < 40, eat meals at regular times, and like the foods to be served in the study.

Exclusion Criteria:

Not dieting to gain or lose weight, not an athlete in training, not taking medications that affect appetite, who have no food restrictions or allergies. Female subjects were required not to be pregnant or lactating. Subjects were excluded if Eating Attitudes Test score was 20 or more, or Zung Self-Rating Scale score was 40 or more.

Description of Study Protocol:

Recruitment

Subjects recruited by flyers and advertisements in local newspapers.

Design

Nonrandomized clinical trial. Within-subject design with repeated measures.

Blinding used (if applicable)

Not applicable.

Intervention (if applicable)

Individuals were told that the purpose of study was to examine perception of taste. Subjects ate lunch in the lab once a week for 4 weeks. Each week they were served 1 of 4 sizes of a deli sandwich (6, 8, 10 or 12 inches) of which they could eat as much as they wanted.

Statistical Analysis

Data analyzed using a linear mixed model with repeated measures. The fixed factor effects in the model were sandwich size and subjects sex; subjects were treated as a random effect. The residuals from the model for food intake were examined for normality and equal variance. The interaction between factors was tested for significance before examining the main effects of the factors. Continuous subject characteristics were tested as covariants in the main model. Subject characteristics of females and males were compared using t tests and chi-square tests. Regression analysis was used to compare the rate of increase in intake with portion size between females and males. In all experimental conditions, consumption of the entire sandwich was defined as leaving less than 25 g uneaten. Results were considered significant at alpha < 0.05, except for post-hoc pairwise comparisons, for which a modified Bonferroni adjustment for multiple comparisons was applied.

Data Collection Summary:

Timing of Measurements

Subjects came to laboratory to be measured for weight and height and complete screening questionnaires (Eating Attitudes Test, Zung Self-Rating Scale, and Eating Inventory).

Dependent Variables

Energy intakes for each meal - foods were weighed before and after the meal to determine amount consumed to 0.1 g
Ratings of hunger and satiety before and after each meal - subjects rated their hunger, thirst, prospective consumption, nausea and fullness on visual analog scales

Independent Variables

Intake of sandwich: subjects came to lab for lunch 1 day per week for 4 weeks and received each of 4 sizes of sandwich: 6" (668 kcal), 8" (892 kcal), 10" (1113 kcal) and 12" (1337 kcal). Order of presentation was randomized across subjects. Subjects were asked to keep meals and activity constant, refrain from consuming alcohol on evening before and morning of each test day, asked not to consume food or caloric beverages 3 hours prior to meal. Subjects completed brief record of physical activity and food intake for evening before and morning of test meal. Sandwiches were served with 1/2 oz potato chips and Andes mint. Subjects were required to eat all potato chips and mint. Subjects were seated alone for lunch and were not allowed to read.

Control Variables

Description of Actual Data Sample:

Initial N: 76 young adults

Attrition (final N): 75 adults, 37 females, 38 males. 1 failed to return after first test meal.

Age: Females: 24.7 +/- 1.1 years, Males: 25.2 +/- 1.1 years

Ethnicity: Not mentioned

Other relevant demographics: BMI females: 22.9 +/- 0.6, males: 24.3 +/- 0.4

Anthropometrics (e.g., were groups same or different on important measures)

Location: Pennsylvania State University

Summary of Results:

	Females sandwich energy intake (n=37)	Males sandwich energy intake (n=38)
6 inch	515 +/- 24 kcal	635 +/- 10 kcal
8 inch	600 +/- 36 kcal	804 +/- 22 kcal
10 inch	619 +/- 35 kcal	919 +/- 31 kcal
12 inch	674 +/- 41 kcal	990 +/- 36 kcal

Other Findings

For both females and males, sandwich intake increased significantly as the portion size of the sandwich increased (P < 0.0001).

The portion size of the sandwich significantly influenced lunch intake for both males and females (P < 0.0001).

78% of males and 35% of females consumed the entire 6 inch sandwich.

When served the 12 inch sandwich, compared with the 8 inch sandwich, females consumed 12% more energy (74 kcal) and males consumed 23% more energy (186 kcal).

When served the 12 inch sandwich, compared with the 6 inch sandwich, females consumed 31% more energy (159 kcal) and males consumed 56% more energy (355 kcal).

Before lunch was served, ratings of hunger did not differ between experimental conditions. After lunch, ratings of hunger were higher after consumption of the 6" sandwich (females: 12 +/- 2 mm, males: 24 +/- 3mm) than after the 3 larger sandwiches (mean for females: 6 +/- 1 mm, males: 9 +/ 2 mm). Ratings of hunger and fullness were not significantly different after eating the 12 inch and 8 inch sandwiches.

Author Conclusion:

These results of this study show that increasing the portion size of a food served as a discrete unit leads to increased energy intake at a single meal without differentially influencing ratings of hunger and satiety. Dietitians should educate their clients about the effect of portion size on food and energy intake and teach strategies for choosing appropriate portion sizes of high-calorie foods, both at home and when dining out.

Funding Source:

Government:

NIH

Reviewer Comments:

Normal weight young adults eating alone, examined only 1 meal, not effect on subsequent intake.

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?		Yes
	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?	Yes
	2.2.	Were criteria applied equally to all study groups?	Yes
	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?	Yes
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)	N/A
	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?	Yes
	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?		N/A
	5.1.	In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate?	N/A
	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.)	N/A
	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?		Yes
	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?	Yes
	7.5.	Was the measurement of effect at an appropriate level of precision?	Yes
	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