EAL

AWM: Portion Control (2006)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To examine the effect of portion size on intake during a single meal, and to investigate whether the response to portion size depended on which person, the subject or the experimenter, determined the amount of food on the plate.

Inclusion Criteria:

Aged 21 - 40 years, in good health, regularly eating 3 meals/day, BMI 20 - 28.

Exclusion Criteria:

Not currently following a weight-loss diet or trying to gain weight, were not using medication known to affect food intake or appetite, were not athletes in training, were not pregnant or lactating, had no food allergies or restrictions that would affect food intake. Subjects were excluded if they scored 30 or more on the Eating Attitudes Test or more than 40 on the Zung Questionnaire or if they reported that they disliked any of the foods to be served at the test meal.

Description of Study Protocol:

Recruitment

Recruited through advertisements in local and university newspapers and posters.

Design

Nonrandomized Clinical Trial. Between-subjects design with repeated measures within each group.

Blinding used (if applicable)

Not applicable.

Intervention (if applicable)

Participants told that study was to examine effects of lunch on taste. Subjects had 1 of 4 portions of macaroni and cheese served to them in 1 group, other group served themselves out of differing portions in serving dish.

Statistical Analysis

Food intake, energy intake, mean duration and VAS ratings were analyzed with use of mixed linear model with repeated measures. The fixed factor effects were portion size and serving method, subjects were treated as a random effect. The interaction between portion size and serving method was tested for significance before examination of the main effects of these factors. The residuals from the model for food intake at lunch were examined for normality and equal variance. Regression analysis was used to calculate the within-subject slope for food intake. t tests were used to compare data on subject characteristics between groups. Subjects who left < 30 g uneaten were considered to have consumed the entire portion. To examine the influence of subject characteristics on the relation between portion size and intake, the factor of subject sex was added to the model. The interactions of serving method, portion size and sex were tested to determine the factors to use in the model. Continuous subject characteristics were then tested as covariates in the model.

Data Collection Summary:

Timing of Measurements

Subjects served lunch 1 day/week for 4 weeks. Measurements of height and weight taken at study beginning, as well as screening questionnaires (Eating Inventory, original-scale Eating Attitudes Test, Zung Self-Rating Depression Scale and Depression Status Inventory, and detailed demographic questionnaire). At end of study, subjects completed discharge questionnaire and Eating-Then and Now questionnaire.

Dependent Variables

Food intake: all food items weighed before and after meal to nearest 0.1 g
Duration of meal recorded to nearest 0.5 min
Hunger and satiety ratings before and after lunch: subjects rated their hunger, thirst, prospective consumption, nausea, and fullness on visual analogue scales

Independent Variables

Food intake: lunch included an entree of macaroni & cheese consumed ad libitum. At each meal, subjects presented with 1 of 4 portions of the entree: 500, 625, 750, or 1000 g. One group of subjects received it portioned on a plate, one group received it in a serving dish and portioned the food themselves. Order of presentation of the portion sizes were balanced across subjects. Subjects asked to keep evening meal and activity level as similar as possible, refrain from drinking alcohol on day before each test day, refrain from eating or drinking (other than water) after 2200 hours, eat a similar breakfast on the morning of each test day, and not eat for 3 hours before and after the test meal. Subjects kept a brief record of their food intake and activity. Lunch was eaten in individuals cubicles and subjects were not allowed to read or do work. Macaroni & cheese was served with 30 g carrot sticks and 17g chocolate bar, which had to be eaten in full.

Control Variables

Description of Actual Data Sample:

Initial N: 59 subjects selected.

Attrition (final N): 51 men and women completed. 5 reported low rating for taste of macaroni & cheese, 2 had scheduling conflicts, 1 withdrew due to illness.

Age: Plate group (n=27): 22.0 +/- 0.4 years, Serving dish group (n=24): 22.5 +/- 0.6 years

Ethnicity: Not mentioned

Other relevant demographics: Plate group BMI: 23.5 +/- 0.4, Serving-dish group: 23.9 +/- 0.4

Anthropometrics: Subjects were assigned to the 2 groups so that the groups were matched for age, sex, BMI, and scores for dietary restraint and disinhibition.

Location: Pennsylvania State University

Summary of Results:

Other Findings

Portion size significantly influenced energy intake at lunch (P < 0.0001) and there was no interaction between serving method and portion size.

Subjects consumed 30% more energy (676 kJ) when offered the largest portion than when offered the smallest portion.

Energy intakes of the 4 conditions of portion size were 2286 +/- 103 kJ, 2553 +/- 126 kJ, 2728 +/- 149 kJ, and 2962 +/- 181 kJ. Intakes in all conditions were significantly different from each other (P < 0.05) except for those between the 625 and 750 g conditions (P = 0.097).

Across all conditions of portion size, no significant differences were found before or after lunch in ratings of hunger, prospective consumption, fullness, thirst or nausea in either group.

Female subjects ate a mean of 30% less food than did male subjects, but the difference was not statistically significant.

The response to the variations in portion size was not influenced by who determined the amount of food on the plate or by subject characteristics such as sex, BMI, or scores for dietary restraint or disinhibition.

Author Conclusion:

The results of this study show that the amount of food that is presented during a single meal directly affects energy intake. Larger portions led to greater energy intake regardless of serving method and subject characteristics. Portion size is a modifiable determinant of energy intake that should be addressed in connection with the prevention and treatment of obesity.

Funding Source:

Reviewer Comments:

Normal-weight and overweight young adults eating alone.

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)	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?	???
	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?		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