NNNS: Effect on Appetite and Food Intake (2011)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

The purpose of the present study was to test the hypothesis that the phenylalanine moiety of aspartame is responsible for its postingestive inhibitory effect on appetite.

Inclusion Criteria:

Adult volunteers.

Exclusion Criteria:

Not described.

Description of Study Protocol:

Recruitment

Not discussed other than subjects were volunteers.

Design

Non-randomized, "with-in subjects" design.

Blinding used

Subjects and experimenter were blind to the identity of the capsules.

Intervention

  • All subjects received each of the four treatments on different days
  • Treatments administered: 200mg L-aspartic acid; 200mg L-phenylalanine; 400mg aspartame; 400mg corn flour (placebo)
  • Each treatment was contained in a single gelatin capsule and was administered with 200ml of tap water.

Statistical Analysis

ANOVA and multiple comparisons among means were made with the Newman-Keules test (and checked using Student's T-test, 2-tail probabilities).

 

Data Collection Summary:

Timing of Measurements

  • Subjects were asked to make visual-analogue ratings of motivation to eat immediately before the treatment and one, 10, 20, 30, 40, 50 and 60 minutes after the treatment
  • Food intake (lunch) was measured one hour after treatment
  • Another set of motivation rating scales was completed immediately after lunch, for three hourly time periods prior to eating their next meal.

Dependent Variables

  • Subjective ratings of motivation to eat before and after treatment and again after the test meal
  • Food intake (kcal) one hour after treatment measured by experimenters.

Independent Variables

Composition of treatment.

 

 

Description of Actual Data Sample:
  • Initial N: 16 (38% male)
  • Attrition (final N): Subject drop-out was not discussed.
  • Age: 20 to 37 years
  • Ethnicity: Not discussed
  • Other relevant demographics: Most of the subjects were undergraduates; none showed excessive concern with eating or their weight
  • Anthropometrics: 15 subjects were normal weight for height (BMI, 22.4±2.8m/kg2); one female was obese (BMI,  52.2)
  • Location: University of Leeds, United Kingdom.
Summary of Results:

 

Mean Food Intakes of Lunchtime Test Meal

Variables

Aspartic Acid

Phenylalanine

Aspartame Control
Kcal consumed at test meal as compared to control -2±533 +47±479 -253±533 * 0±485

 * Significantly different from other three treatments (P<0.01).

Other Findings

There were no significant differences between treatment groups in motivational ratings (before lunch and after lunch).

Author Conclusion:

The findings confirm aspartame suppresses food intake but contrary to the study's hypothesis, this is not due to an individual action of the phenylalanine moiety.

Funding Source:
Government: A grant from the Agricultural and Food Research Council
Reviewer Comments:
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) No
 
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? No
  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? No
  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%.) No
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? ???
  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? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? Yes
  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.) Yes
  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? No
  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? 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? No
  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)? N/A
  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? No
  9.1. Is there a discussion of findings? No
  9.2. Are biases and study limitations identified and discussed? No
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