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

To determine whether aspartame has a negative effect on cognitive performance.

Inclusion Criteria:

Students at the University of Illinois.

Exclusion Criteria:
  • Use of prescription medications or illicit drugs
  • Presence of phenylketonuria.
Description of Study Protocol:


Healthy college students.


Counter-balanced, double-blind, within-subject RCT.

Blinding Used

Counter-balanced, double-blind, within-subject.


Subjects received either placebo capsules or aspartame capsules (50mg per kg of body weight per day) for nine days, or an acute dose of ethyl alcohol to achieve 0.1% blood ethanol levels as described earlier. All participants received the placebo and ethanol treatments once and the aspartame treatment twice with a seven-day interval. Blood phenylalanine and breath alcohol levels were measured.

Statistical Analysis

  • SPSS used for descriptive statistics comparing subject responses to those of a database of 400 other subjects entered in the SPARTANS (Simple, Portable, Aviation Relevant Test-battery and ANswer-Scoring system) designed to test perceptual-motor abilities, spacial abilities, working memory, attentional performance, risk-taking, reasoning, processing flexibility and planning or sequencing ability
  • One-way repeated measures ANOVA on each battery subtask in the SPARTANS battery
  • Pairwise comparisons where condition was found to have significant effect on test scores (to determine source of effect)
Data Collection Summary:

Timing of Measurements

  • Pre-test and post-test administered (no dosing administered)
  • At the end of the nine-day dosing period, subjects gave blood that was tested for blood phenylalanine and blood alcohol; they also had a breath analyzer test and were then immediately given a cognitive test battery
    • Group One: Pre-test; placebo times nine days; alcohol; aspartame times nine days; aspartame times nine days; post-test
    • Group Two: Pre-test; aspartame times nine days; aspartame times nine days; placebo times nine days; alcohol; post-test.

Dependent Variables

  • Cognitive test (Simple Portable Aviation Relevant Test battery and ANswer-scoring System)
  • Plasma phenylalanine levels (plasma blood)
  • Alcohol (plasma blood and breath analyzer).

Independent Variables

Aspartame (50mg per kg of body weight).

Control Variables

  • Placebo (negative control)
  • Alcohol (positive control)
  • Time of day (to guard against effect of circadian rhythm).


Description of Actual Data Sample:
  • Initial N: 12 (gender not given)
  • Attrition: None
  • Other relevant demographics: All were University of Illinois students
  • Location: Urbana-Champagne, IL. 
Summary of Results:

No deleterious effects of aspartame were detected upon cognitive performance.


After Nine Days of Placebo

After Nine Days of 50mg Aspartame per kg of Body Weight 

After Alcohol Treatment

Statistical Significance of Group Difference

Blood phenylalanine level





Blood alcohol





 Other Findings

Significant correlation between blood phenylalanine level and higher total score on the Schedule task (R=0.77, P=0.004).

Author Conclusion:

Aspartame caused no detectable cognitive deficits. Ethanol was, however, detrimental to performance.

Funding Source:
Government: FDA and FAA
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? No
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
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? 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? Yes
  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)? Yes
  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? 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