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Adult Weight Management

AWM: Portion Control (2006)

Citation:

Rolls BJ, Roe LS, Kral TVE, Meengs JS, Wall DE.  Increasing the portion size of a packaged snack increases energy intake in men and women.  Appetite 2004; 42: 63-69.

PubMed ID: 15036784
 
Study Design:
Non-Randomized Controlled Trial
Class:
C - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To determine how the portion size of a packaged snack affects energy intake of the snack and of the subsequent meal.
Inclusion Criteria:
Aged 20 - 45 years, BMI 20 - 40, regularly ate 3 meals/day, regularly snacked between meals and liked potato chips.
Exclusion Criteria:
Subjects were not dieting to gain or lose 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 food restrictions that would affect food intake, and were not smokers.  Subjects excluded if BMI outside 20 - 40, if scored >30 on Eating Attitudes Test, if scores > 40 on Zung Self-Rating Questionnaire, or if they disliked any foods to be served in the study. 
Description of Study Protocol:

Recruitment

Recruited by newspaper advertisements.

Design

Nonrandomized Clinical Trial.  Within-subjects design with repeated measures.

Blinding used (if applicable)

Not applicable.

Intervention (if applicable)

Subjects reported to lab on 5 separate days to eat an afternoon snack and dinner.  On afternoon of each test day, subjects were served 1 of 5 package sizes of potato chips and then had dinner.

Statistical Analysis

Food intake and visual analog scale ratings were analyzed using a linear mixed model with repeated measures, which took into account the time-dependent nature of the repeated observations.  The fixed factor effects were snack package size and subject sex, subjects were treated as a random effect.  A modified Bonferroni adjustment was applied for post-hoc pairwise comparisons between experimental conditions.  Continuous subject characteristics (age, weight, height, BMI and scores for dietary restraint, disinhibition, hunger, depression, and eating attitudes) were tested as covariates in the mixed model.  Subject characteristics for males and females were compared using t tests.  Differences in means were considered significant at p < 0.05.

Data Collection Summary:

Timing of Measurements

Potential subjects came to lab for height and weight measurements and to complete questionnaires (Eating Attitudes Test, Zung Self-Rating Questionnaire, Eating Inventory).  On 5 separate days, subjects ate an afternoon snack and returned 3 hours later for dinner in individual cubicles.  Upon study completion, subjects completed discharge questionnaire.

Dependent Variables

  • Questionnaires about physical well-being, food intake, medications, andn alcohol intake
  • All food intake was weighed to nearest 0.1 g 
  • Characteristics of potato chips rated using visual analog scales
  • Subjects also completed ratings of hunger and fullness using visual analog scales at 6 time points:  immediately before and after the snack, 1 and 2 hours after completion of snack, and before and after dinner

Independent Variables

  • Snack intake:  for each snack, subjects were served 1 of 5 packages of potato chips (28, 42, 85, 128 or 170 g) which they consumed ad lib.  Subjects then returned to lab for dinner which was also ad lib.  Order of presentation of package sizes was balanced among subjects.  Subjects were asked to not drink anything except water, refrain from drinking water for 1 hour prior to lunch and dinner, maintain a consistent activity level on day before and day of each test session, and keep a brief record of food intake and physical activity.  Subjects ate in individual cubicles and were allowed to read magazine without articles relating to snack intake, weight loss, or emotionally disturbing news.

Control Variables

 

Description of Actual Data Sample:

Initial N: 68 subjects

Attrition (final N):  63 subjects completed study.  5 withdrew for personal reasons or schedule conflicts.  3 subjects were excluded from analysis due to repeated low snack intakes (< 10 g at 3 or more sessions).  Final sample composed of 60 subjects, 34 females, 26 males.

Age:  Females:  22.3 +/- 0.6 years; males:  23.5 +/- 1.2 years 

Ethnicity: Not mentioned

Other relevant demographics: BMI females:  22.4 +/- 0.5, males: 24.3 +/- 0.6

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

Location:  Pennsylvania State University 

 

Summary of Results:

 

Females (n=34) - kJ

Males (n=26) - kJ

Snack intake - 28 g 567.6 +/- 21.2 592.5 +/- 14.9
Snack intake - 42 g 774.1 +/- 38.7 885.4 +/- 30.3
Snack intake - 85 g 1135.9 +/- 80.7 1381.2 +/- 114.5
Snack intake - 128 g 1235.6 +/- 92.2 1851.8 +/- 128.8
Snack intake - 170 g 1335.8 +/- 110.6 1892.4 +/- 186.4
Dinner intake - 28 g 3881.2 +/- 196.0 5193.8 +/- 263.6
Dinner intake - 42 g 3825.6 +/- 170.5 4932.4 +/- 289.0
Dinner intake - 85 g 3653.3 +/- 183.9 4881.6 +/- 195.5
Dinner intake - 128 g 3487.3 +/- 126.4 5140.6 +/- 275.9
Dinner intake - 170 g 3708.5 +/- 147.7 4514.2 +/- 192.3
Snack + dinner - 28 g 4448.8 +/- 206.0 5786.3 +/- 265.1
Snack + dinner - 42 g 4599.7 +/- 191.4 5817.8 +/- 298.5
Snack + dinner - 85 g 4789.3 +/- 219.9 6262.9 +/- 246.3
Snack + dinner - 128 g

4722.9 +/- 173.6

6992.3 +/- 353.9

Snack + dinner - 170 g

5044.3 +/- 181.8

6406.5 +/- 306.9

Other Findings

Results showed that snack intake increased significantly as the package size increased for both males and females (p < 0.0001).

Women had a smaller absolute intake of snack than did men; from the largest package size, females ate 71% as much snack as the males did.  In females the increase in intake began to level off at the 128 g package, while in male subjects this pattern began with the 170 g package.

The increase in snack intake from the smallest to the largest package size was 768 kJ (184 kcal) for women and 1300 kJ (311 kcal) for men.

The combined energy intake from snack and dinner also increased as the package size increased. 

The relationship of package size to snack intake was not significantly influenced by any subject characteristics other than sex (age, height, weight , BMI, scores for depression, disordered eating attitudes, dietary restraint, disinhibition, or hunger, the reported frequency of cleaning the plate, or whether or not potato chips were a usual snack food).

In female subjects, the package size of potato chips had no significant effect on energy intake at dinner (p = 0.199).  In male subjects, there was a significant effect of snack package size on dinner intake (p = 0.001), with a significant decrease in intake following the largest snack package.

When snack and dinner intakes were considered together, however, as the package size increased, the combined energy intake at snack and dinner also increased for both women (p < 0.023) and men (P < 0.0001).

On average, when served the largest snack package compared to the smallest, subjects consumed an additional 596 kJ (143 kcal) at snack and dinner combined.

Initial ratings of hunger before the snack was served did not differ across experimental conditions.  Between the snack and dinner, there was no interaction between package size and time.  Ratings of hunger between the snack and dinner decreased significantly with increasing package size at all time points (p < 0.001) but did not differ by sex.

Author Conclusion:
The results from this study demonstrate that the portion size of a packaged snack directly affects the amount of that snack that is consumed.  Furthermore, in most cases individuals did not significantly reduce intake at dinner to compensate for the increased energy intake from the snack.  The only exception was that in male subjects, mean energy intake decreased at dinner following the largest snack package.  Overall, however, increasing the portion size of the snack increased short-term energy intake.  These data suggest that the availability of large packages of energy-dense snacks may be one of the environmental influences associated with excess energy intake.
Funding Source:
Government: NIH
Reviewer Comments:
Normal-weight young men and women, eating alone.  Effect on subsequent intake was 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? Yes
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? N/A
  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? 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? N/A
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