NNNS: Appetite (2006)

Study Design:
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Quality Rating:
Research Purpose:
To study the effects on appetite, food intake and food selection of consuming different volumes of a carbonated mineral water (CMW) pre-load in combination with aspartame (APM), as either a pill or a sweetener.
Inclusion Criteria:
Exclusion Criteria:
  • Smoking
  • Following a vegetarian diet
  • Diagnosis of phenylketonuria
  • Food allergy
  • Major illness
  • Receiving medications.
Description of Study Protocol:


  • By posters placed throughout the University of Toronto and by word of mouth
  • Subjects gave informed consent to participate in the study, approved by the University of Toronto Human Subjects Review Committee. 



Experimental Schedule

Time Procedure
10:00 p.m.  night before Subject fasts 
7:45 a.m. Subject arrives at feeding studies laboratory
8:00 a.m. Subject consumes breakfast
9:30 a.m. VAS motivation to eat; VAS food appeal
10:55 a.m. VAS motivation to eat; VAS food appeal
11:00 a.m. Treatment preload
11:05 a.m. VAS motivation to eat
11:10 a.m. VAS motivation to eat
11:15 a.m. VAS motivation to eat
11:20 a.m. VAS motivation to eat
11:30 a.m. VAS motivation to eat; VAS food appeal
11:45 a.m. VAS motivation to eat
12:00 p.m. VAS motivation to eat; VAS food appeal
12:05 p.m. Buffet lunch served
12:30 p.m. VAS motivation to eat; VAS food appeal

Experimental Design and Aspartame Content of Soft Drinks

Treatment Pre-Load Aspartame (mg) Consumption (minutes)
A 280ml carbonated mineral water (control) 0 10
B 560ml mineral water 0 10
C 280ml mineral water plus encapsulated APM 340 10
D 280ml mineral water plus APM sweetener 340 10
E 560ml diet soda 340 (precise amounts depended upon the diet soda consumed) 10

Subjects were asked to select one soft drink flavor from a choice of Sprite, 7-Up, orange, ginger ale, root beer or cream soda to be consumed during the study.


  • Consumed entirely within the 30 minutes, breakfast meal size was dependent on subject's weight, such that it provided 25% of the estimated daily caloric intake, based on average expenditures for height and weight
  • Energy content of the meal was regulated by altering the amount of cereal and milk presented for consumption.


  • Treatment was administered at 11:00 a.m. and fully randomized
  • All treatments were served cold in 300-ml cups
  • Subjects consumed all beverages at a rate that ensured half of the drink was consumed in the first five minutes and the entire drink completed in no less than nine minutes and no more than 10 minutes
  • For Treatment C, the APM was administered as two gelatin capsules (each containing 170mg APM) consumed 2.5 and 7.5 minutes after drinking began
  • Treatment E subjects were unaware of the nature of the soft drink.


  • Each subject was served an individualized buffet lunch and instructed to eat until comfortably full within the 30 minutes of allotted time
  • Macronutrient content was constant across the lunches and was the same at each test session.

Blinding Used

Treatment E subjects were unaware of the nature of the soft drink.

Statistical Analysis

  • An ANOVA done with all five treatment conditions allowed a general statement about the effects on appetite and food intake. Because responses to food vary between individuals of high and low restraint, a secondary analysis was done with "restrained/non-restrained" as an addtional main effect. All post hoc analyses were done using Tukey's post hoc comparisons.
  • Food intake and selection: The effect on treatment on total energy intake was assesssed by a one-day repeated-measures ANOVA. Macronutrient selection was analyzed through a two-way repeated-measures ANOVA (treatment x macronutrient).
  • Visual analog scales: Baseline VAS scores were taken at 10:55 a.m., five minutes prior to consumption of the pre-load and all changes in appetite were taken relative to baseline. VAS scores of subjective appetite were analyzed by two-way repeated-measures ANOVAs and food appeal were grouped by major component and analyzed through three-way ANOVAs.
Data Collection Summary:

Timing of Measurements

  • Weight
  • Height
  • Restrained eaters questionnaire
  • Food liking checklist
  • Food acceptability list.

Food Intake and Selection

  • Amount consumed during lunchtime was measured
  • Total energy intakes, protein, carbohydrate and fat was calculated
  • Macronutrient composition was calculated from manufacturers and food composition tables.

Visual Analog Scales

  • Subjective appetite and food appeal were measured throughout the morning using VAS continuous 10cm lines word-anchored at each end. Subjective appetite VAS asessed desire to eat, hunger, fullness and prospective consumption.
  • The food appeal VAS measured the appeal of 32 commonly available foods, portion sizes of which were equated for energy content.
Description of Actual Data Sample:
  • Initial N: 18 males
  • Age: 19 to 25 years
  • Anthropometrics: BMI, 21kg/m2 to 25kg/m2.


Summary of Results:
  • Treatment had no effect on food intake or macronutrient selection
  • Both 560ml of CMW or soft drink suppressed appetitie, although 280ml of APM-sweetened mineral water significantly increased subjective appetite realtive to the control
  • Encapsulated APM had no effect on appetite.

Food intake and selection

  • Neither treatment nor test session had a significant effect on total caloric intake at lunch-time meal
  • Macronutrients were not consumed in equal amounts (P<0.001), post hoc analyses showed that subjects ate more fat than CHO or protein and more CHO than protein. However, there was no treatment effect or treatment x macronutrient interaction.

 Subjective Appetite

  • Treatment had a significant effect on prospective consumption (P<0.02) and a marginal effect on desire to eat. There were no treatment effects on hunger or fullness.
  • Increasing the volume of the drink from 280ml of mineral water to 560ml significantly reduced all four measures of subjective appetite (smallest P<0.02)
  • The subjective appetite following consumption of 560ml of mineral water was not different from that following consumption of 560ml of the APM-sweetened soft drink
  • Consuming APM as a pill (without taste) did not significantly reduce subjective appetite, compared to the mineral water control
  • Consuming 340mg APM as a sweetener significantly increased all four measures of hunger (smallest P<0.02). 

Food Appeal

  • Comparisons of treatments (effect of volume, effect of APM pills and effect of mineral water vs. diet pop) showed no treatment effects. Subjects found foods generally less appealing after the APM-sweetened mineral water pre-load, compared to the mineral water alone (P<0.05).
  • In all treatment comparisons, food appeal increased from 10:55 a.m. to 12:00 p.m. and declined after lunch, with CHO foods being more appealing than fat and low-calorie foods (all P<0.05). Analysis of time x major component increased in appeal more rapidly than fat and low-calorie foods (all P<0.05).

Restrained Eaters

There were no differences between restrained and non-restrained eaters in the size of lunchtime meal, nor any group interaction x treatment interaction.


Author Conclusion:

Appetite reduction following consumption of an APM-sweetened drink is likely due to drink volume and not the APM content. Consuming APM-sweetened CMW produces a short-term increase in subjective appetite.

Limitations and Biases

  • Differences in experimental design
  • Measured food intake at wrong time
  • Intense sweetener used in the study.


Funding Source:
Government: National Institute of Nutrition (Canada)
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? N/A
  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? No
  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