EAL

AWM: Portion Control (2006)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To determine the combined effects of energy density and portion sizes on energy intake in women.

Inclusion Criteria:

Female, 20-45 y of age, in good health, nonsmoking, not dieting, not in athletic training, not pregnant or lactating, not using medications known to affect food intake or appetite, consuming meals (including breakfast) at regular intervals, no change in body weight (+4.5 kg) in the previous 6 mo., no food allergies or restrictions. After pre-testing, normal weight and overweight (BMI between 19 and 29.9) women who scored <20 on the EAT-26 and <40 on the Zung Depression Scale, and who were unaware of the purpose of the research were accepted into the study.

Exclusion Criteria:

As listed above.

Description of Study Protocol:

Recruitment Advertisements in the local university community

Design: Nonrandomized clinical trial - within subjects design with repeated measures.

Blinding used (if applicable) NA

Intervention (if applicable): Lunches of varying energy density and portion size once per week for 6 weeks.

Statistical Analysis Food intake (g), energy intake (kJ), VAS ratings, and change in VAS ratings before and after meals were analyzed with a mixed linear model with repeated measures. The fixed-factor effects were energy density and portion size, with subjects treated as a random effect. The interaction between energy density and portion size was tested for significance before analyzing the main effects of these factors. The residuals from the model for food and energy intakes were examined for normality and equal variance. Mean intakes were analyzed both with and without subjects who cleaned their plate. The effect of subject characteristics on the main outcome was analyzed by ANCOVA. Regression analysis was used to identify significant predictors of food intake. Tukey's test was used for post hoc pairwise comparisons of means for significant effects.

Data Collection Summary:

Timing of Measurements Potential subjects came to laboratory for height and weight measurements and to complete screening questionnaires (Demographic and Health questionnaire, Eating Inventory, Eating Attitudes Test, Zung Self-Rating Depression Scale and Dutch Eating Behavior Questionnaire). Once a week for 6 weeks, subjects served breakfast, lunch and dinner ad lib. All meals were scheduled at the same time on all test days, with a minimum of 4 h between breakfast and lunch and 4.5 h between lunch and dinner.

Dependent Variables

All foods weighed before and after each meal to nearest 0.1 g
Percentage body fat determined by bioelectrical impedance analysis
Energy intake (kJ) of food consumed at lunch and for the total day
Completed questionnaire about physical well-being, medications, alcohol consumption.
Visual analog scales used to measure hunger, thirst, prospective consumption, nausea, fullness, palatability, comparison of portion size with subject's usual portion size, estimation of amount of fat and salt in each food.

Independent Variables

Main entree at lunch was formulated in 2 versions varying in energy density (5.23 vs 7.32 kJ/g), each of which was served in 3 different portion sizes (500, 700 or 900 g), matched for macronutrient composition and palatability. Entrees assembled in lab by trained research personnel. Breakfast and dinner were standard. Women instructed to refrain from eating and drinking (except water) after 2200 the night before each test day, not to consume alcohol during the previous 24 hours and maintain similar exercise levels throughout the day. Subjects seated in individual cubicles.

Control Variables

Description of Actual Data Sample:

Initial N: 45 women

Attrition (final N): 39 completed. 3 withdrew before the study began for personal reasons, one subject withdrew after her 2nd session, 2 subjects did not meet the minimum requirements for intake (>100 g) and ratings of pleasantness of taste (>35 mm) of the manipulated entree.

Age: Mean age 23.4+1 years (range 20-44)

Ethnicity: not stated

Other relevant demographics: Mean BMI 23.1 +/- 0.41 (range 19.3 - 29.7)

Anthropometrics: Subject characteristics are only reported for the entire group.

Location: U.S. - Pennsylvania

Summary of Results:

Other Findings

There was a significant effect of portion size (P < 0.0001) and energy density (P < 0.0001) on the weight of food and energy intake consumed at lunch. The interaction between the factors was not significant (P = 0.09 for weight, P = 0.27 for energy intake) indicating that the portion size and energy density of foods act independently to affect amount of food consumed.

Increases in portion size and energy density led to independent and additive increases in energy intake (P < 0.0001).

Subjects consumed 56% more energy (925 kJ) when served the largest portion of the higher energy-dense entree than when served the smallest portion of the lower energy-dense entree. Subjects consumed 20% more food when served the largest portion vs smallest portion, and 10% more food when served higher energy density than lower energy density.

Subjects did not compensate for the additional intake by eating less at subsequent meals. Food intake at breakfast and dinner did not differ between conditions (P > 0.05).

Despite substantial differences in energy intake, no systematic differences in ratings of hunger and fullness across conditions were observed.

When all meals were considered together, there was an effect of portion size (P=0.003) and energy density (P<0.0001) on total daily energy intake.

Subjects rated the pleasantness of the odor of the low density entree higher than the high density entree (P=0.02).

None of the subject characteristics (age, body size, dietary restraint, disinhibition, depression, and eating attitudes) resulted in changes in intake in the different conditions. However, in regression analyses the combination of these factors predicted an additional 16% of the variance in the food intake at lunch.

Author Conclusion:

The findings from this study showed that when both the energy density and the portion size of a food are increased, both factors act independently to affect energy intake. In conclusion, the results from this experiment provide evidence that the energy density and the portion size of foods add together to independently affect energy intake. This association is of particular importance in that it identifies the availability of large portion sizes of energy-dense foods as a significant contributor to increased energy intakes. The understanding of this relation can aid in the development of dietary strategies to prevent and treat obesity.

Funding Source:

Government:

NIH

Reviewer Comments:

Normal weight and overweight women eating alone. Subject characteristics did not make a difference. Subsequent meal intake studied.

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?	???
3.	Were study groups comparable?		N/A
	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?	N/A
	3.3.	Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.)	N/A
	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?		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?	N/A
	6.6.	Were extra or unplanned treatments described?	N/A
	6.7.	Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups?	N/A
	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