NNNS: Appetite (2006)

Study Design:
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Quality Rating:
Research Purpose:
The purpose of the study was to measure the anorexic effect of capsulated aspartame taken at different intervals before eating.  
Inclusion Criteria:
  • Not currently dieting to lose weight
  • Dietary restraint score (10) was less than equal to 16
  • Non-smoker
  • Body mass index was within the range 18 to 25kg/m2
  • Healthy men and women.
Exclusion Criteria:
Description of Study Protocol:


  • Recruited by advertisements circulated within the University of Leeds

  • Not paid for participation in the study

  • Protocol was approved by the Leeds University Deparatment of Psychology Ethics Committee.


Subjects were divided into three groups, each with six men and six women, matched on restraint core and BMI.

  • Group A: Received treatments five minutes before the beginning the test meal

  • Group B: Received treatments 30 minutes before the test meal

  • Group C: Received treatments 60 minutes before the test meal.


Each subject received two treatments exactly one week apart. Treatments were:

  • 400mg aspartame and 400mg corn flour were each administered in a single, size 0, white gelatin capsule, swallowed with 50ml of tap water.

  • Six subjects in each group were given asparatame on the first week and placebo on the second week, with the remaining subjects given the treatment in reverse order. 

Blinding Used

  • Half of the subjects within each of the groups were tested by one experimenter and the other half by a second experimenter

  • Subjects were fully blind to the contents of the capsules

  • The identity of the capsules was concealed from the experimenters for the duration of the study by using a code assigned and kept by a collegue not involved in the work.   

Statistical Analysis

  • Food energy consumed in the test meal was calculated from energy values published in food composition tables and manufactuters' labels.

  • ANOVA and multiple comparisons among means were done with the Newman-Keuls test and checked with the student's T-test (two-tail probabilities).

Data Collection Summary:

Timing of Measurements

  • Before the start of the study, volunteer subjects attended a brief meeting, during which, they were given a description of the study and questionnaires to be used. Information on their food preferences was collected and used to adjust the menu for the test meal to suit individual tastes.
  • Test days: Subjects ate breakfast in the laboratory between 8:00 and 9:00 a.m. The meal was the same on both occcasions (cereal or toast plus tea or coffee).
  • Following breakfast, they were allowed to drink only water and a maximum of one cup of tea or coffee before returning to the laboratory at 11:50 a.m. and seated in individual cubicles
  • At 12:00 noon and at 10 minute-intervals up to and including 1:00 p.m., subjects rated hunger, desire to eat, fullness and thirst on 150mm line scales 
  • Ratings were also completed immediately after swallowing the capsule with water and after finishing the test meal at around 1:20 to 1:30 p.m.   
  • Group C took the capsule at 12:01 p.m., Group B at 12:31 p.m. and Group A at 12:56 p.m. During the intervals between procedures, subjects were allowed to read and relax
  • Test meal: Served at 1:01 p.m., consisting of 16 sandwich quarters (two varieties of fillings), salad, fresh fruit, sweet biscuits and a cold dessert (yogurt, fruit jelly, canned fruit salad or rice pudding). This amount offered at least 2,000kcal and was well in excess of the subject's usual intake. Water was available to drink with the meal. The same menu was given on each of the two test days. 
  •  Foods were weighed before and after meal to the nearest 0.1 gram.
Description of Actual Data Sample:
  • Initial N: 36 (18 men, 18 women)
  • Age: 18-30 years
  • Anthropometrics: Body mass index was within the range of 18kg/m2 to 25kg/m2
Summary of Results:

Motivation to Eat Ratings

  • Three-way ANOVA (time of administration, treatment and time as factors) revealed a statistically significant main effect of time (P<0.001) due mainly to the reduction in hunger following the test meal; no other significant effects
  • Non-significant effects involving treatment were: Main effect of treatment, treatment by time of administration, treatment by time, treatment by time of administration by time.
  • Overall, the level of hunger before and after the meal was unaffected by administration of aspartame.
  • Thirst ratings: Significant time of administration by time interaction (P<0.001) for thirst, due to a decline in thirst following the consumption of the capsule and water, which occurred at different times for the different groups. 

Food Intake

  • Significant interaction effect on time of administration and treatment as factors carried out on the results for test meal intake.
  • Not significant were the main effect of time of administration and the main effect of treatment
  • Aspartame reduced food intake compared with placebo, when administered 60 minutes before the start of the test meal (P<0.01), but not when administered either 30 or five minutes before the start of the test meal.
Author Conclusion:
  • Capsulated aspartame reduced food intake when taken 60 minutes before, but not when taken either five or 30 minutes before eating a test meal. In contrast, there were no significant effects of aspartame on pre-meal ratings of hunger, desire to eat or fullness for any of the groups. 
  • Results confirm a post-inhibitory action of aspartame on appetite, which may involve the amplification of the satiating effects of food. The lack of effect of aspartame administered at the shorter intervals before eating suggests a post-gastric or even post-absorptive mechanism of action. This observation is important for the possible therapeutic exploitation of the anorexic effect of capsulated aspartame.
Limitations and Biases
  • May help in dietary treatments for obesity
  • There is need to assess the delay of eating for at least an hour after taking aspartame and also test the effectiveness in reducing intake when taken repeatedly over a number of days.
Funding Source:
University/Hospital: University of Leeds
Foundation associated with industry:
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) 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%.) N/A
  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? 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? 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? N/A
  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