NNNS: Effect on Appetite in Adults (2010)

Citation:
 
Study Design:
Class:
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Quality Rating:
Research Purpose:
  • To determine whether human brain activation is different for caloric sucrose compared to an artificial sweetener. It was hypothesized that sucrose would elicit greater brain activation compared to the artificial sweetener sucralose (Splenda) in the FO/AI and reward pathways, including the midbrain ventral tegmental area (VTA) and nucleus accumbens.
  • To test whether they could measure brain taste-pathway activation for the two sweet taste stimuli using brain imaging that is consistent with the neuro-anatomical literature. Researchers hypothesized that both sweeteners would activate primary brain taste centers (FO/AI) and related areas such as cingulate, striatum, thalamus and orbitofrontal cortex.
  • To study if individual "liking" or pleasantness for sweet taste predicts brain activation and if there is a subset of the taste pathway that is specific for the pleasantness response. Researchers hypothesized that the insula and the dopaminergic reward-related ventral striatum or the ventral tegmental midbrain might be implicated in this response.
Inclusion Criteria:
  • Healthy
  • Normal weight
  • Normal menstrual cycles.
Exclusion Criteria:
  • None specifically listed
  • Clinical interviews and self-assessments were applied in order to assure control status
  • Subjects were screened and assessed for Axis I psychiatric illness with the Structural Clinical Interview for DSM-IV Axis I disorders
  • No participant had a history of an eating disorder or any psychiatric, serious medical or neurological illness
  • Participants were not on medications, including herbal supplements
  • In order to avoid sub-threshold disordered eating, the investigators applied the Eating Disorders Inventory-two that showed normal values for body dissatisfaction, bulimic symptoms and drive for thinness.
Description of Study Protocol:

Recruitment

Local advertisements.

Design

  • Cross-sectional taste tests
  • Treatments were given in random order for the taste tests
  • For brain imaging, six blocks of taste stimulation were used and the block order fully randomized across subjects.

Blinding Used

Treatments were given blindly and in random order for the taste tests.

Intervention

  • Sucrose (0% to 32%)
  • Sucralose (Splenda; concentrations were matched to sucrose for sweetness).

Statistical Analysis

  • Behavioral testing:
    • The hedonic pleasantness scale ranged from one ("like not at all") to  nine ("like extremely"), where five is "neither like nor dislike"
    • A linear statistical equation was used in order to calculate pleasantness slope for sucrose and sucralose. Using the linear slope assesses the rate of change of pleasantness ratings as a function of sucrose concentration. This serves as a proxy measure for pleasantness sensitivity.
    • Behavioral data were analyzed with SPSS14 statistical software
  •  Comparison of taste stimuli:
    • Voxel-wise percent signal change data for the whole brain were entered into unpaired T-tests for main effect BOLD response differences in sucrose and sucralose stimulations; data were also entered into paired T-tests for differences in BOLD response comparing sucrose and sucralose conditions
    • Main effect statistical maps were thresholded at P<0.005 and 1,024uL (minimum of 16 contiguous voxels)
    • Comparison maps subtracting sucrose from sucralose were thresholded at P<0.05 and 512uL (minimum of eight contiguous voxels)
    • In order to avoid confluent regions of interest, an anatomical mask was applied on the statistical maps to retrieve activity data related to the taste pathway: Midbrain, thalamus, caudate, putamen, anteroventral striatum, insula, anterior cingulate and orbitofrontal cortex
    • Percent signal change data were extracted from regions of interest (ROIs) that survived this thresholding, clustering and masking protocol. Those percent signal change data were also used to assess correlation or regression analyses with behavioral data defined in the hypotheses.
  • Taste pathway analysis, functional connectivity analysis:
    • The FO/AI as the primary taste cortex was selected as seed regions in order to assess taste pathway-related areas. We selected the main effect statistical results for sucrose and sucralose in the FO/AI as seed regions.
    • Voxel-wise correlation coefficients were Fisher Z transformed
    • A paired T-test was performed for each seed ROI that contrasted the Fisher Z transforms of the correlation coefficient in the sucrose and sucralose conditions, so as to determine differences in functional connectivity between conditions
    • A voxel-wise regression analysis was used to correlate functional connectivity data with the pleasantness slope for each subject.

 

Data Collection Summary:

Timing of Measurements

One-time measurements.

Dependent Variables

  • Sweetness ratings
  • Pleasantness relation with sweetness
  • Pleasantness slope
  • Taste pathway analysis
  • Functional connectivity.

Independent Variables

  • Sucrose
  • Sucralose (Splenda).

Control Variables/Procedures

  • Subjects were screened extensively at the beginning of the study to rule out factors which could influence the results
  • To reduce cognitive bias, sucrose and sucralose solutions were given blindly and in random order
  • Subjects were allowed to wash their mouth with distilled water between taste stimulations to order to avoid desensitization to or overload from the sweet tastes.

 

Description of Actual Data Sample:

Initial N

13 women.

Attrition (Final N)

  • 12
  • One woman was excluded because she could not fulfill the criteria for behavioral matching of sweet solutions at any concentration tested.

Age

20 to 36 years (mean 27±6 years).

Anthropometrics

  • Current BMI between 20 and 25 (mean 22±2), with a mean low lifetime BMI of 21±1, with a high lifetime BMI of 23±2
  • Normal menstrual cycles; subjects were studied only during the first 10 days of the menstrual cycle because brain reward mechanisms vary depending on the reproductive phase.
Summary of Results:

Findings

  • Taste behavioral measures:
    • Sweetness ratings correlated highly with concentration for sucrose (Pearson correlation mean R=0.9, P<0.0001, range from R=0.86, P+0.03 to R=0.99, P<0.0001) as well as sweetness and concentrations for sucralose (Pearson correlation mean R=0.8, P<0.0001, range from R=0.5, P+0.3 to R=0.99, P+0.0001)
    • Pleasantness relation with sweetness was more variable for either sucrose (Pearson correlation mean R=-0.09, P=0.4, ranging from R=-0.97, P=0.002 to R=0.96, P=0.002) or sucralose (Pearson correlation mean R=0.03, P=0.8, ranging from R=-0.76, P=0.07, to R=0.97, P=0.001).
    • The individual subject slopes for the pleasantness measure were then calculated. This resulted in slopes ranging from sucrose from -0.25 to 0.28 and for sucralose from -0.24 to 0.2. The pleasantness slopes for sucrose and sucralose showed a very high correlation (Pearson R=0.8, P=0.001).
  • fMRI results:
    • The main effect of sucrose stimulation revealed bilateral activation in the FO/AI (extending from the frontal operculum to the inferior insula), left ventral striatum, anterior cingulate and bilateral midbrain
    • Sucralose stimulation also activated the FO/AI bilaterally to a similar extent when compared to sucrose-related activation, but no other area
    • In addition, both sucrose and sucralose activated bilateral sensorimotor cortical areas
    • Within the anatomical regions of interest, overlaid on the statistical maps, sucrose was found to induce significant activation in 10 regions. In comparison, sucralose administration resulted in significant activations in only three of the a priori determine regions (as shown in Table 1).
    • In order to relate subjective assessments of pleasantness with fMRI percent signal change, a regression analysis was conducted with pleasantness ratings as the independent variable and signal change as the dependent measure. The FO/AI activation was selected as imaging variable since it is the primary taste cortex and that area was activated similarly across conditions. This analysis showed that pleasantness slopes predicted left insula activation for both sucrose (P=0.01) and sucralose (P=0.03) conditions. In comparison, there was only a tendency for pleasantness slopes to predict right-sided insula activation for both sucrose (F=2.7, P=0.1) and sucralose (F=2.6, P=0.1) administration. 
  • Sucrose vs. sucralose comparison:
    • A direct comparison of activation due to sucrose or sucralose administration revealed greater activation for sucrose in the bilateral FO/AI; other ROIs were localized to the left caudate, left cingulate and bilateral superior frontal cortex, in addition to the posterior part of the anterior insula bilaterally
    • Overall, there was a similar pattern of connectivity for sucrose and sucralose, with seed regions in the left FO/AI being correlated with activation in the contralateral insula, ipsilateral ventral and middle striatum and pallidum, bilateral anterior cingulate and ipsilateral thalamus
    • The right FO/AI activation was correlated with contralateral insula, bilateral anterior cingulate and bilateral thalamus; no correlation of activity was found for the striatum
    • Functional connectivity analysis showed a higher connectivity in the sucralose condition compared to sucrose for ROIs one and two for sucrose and ROIs 11 and 12 for sucralose
    • For sucrose, pleasantness slopes predicted connectivity of ROI  one with the contralateral insula and midbrain, including the substantia nigra/VTA. These findings were absent in the sucralose condition.
    • Pleasantness slopes predicted connectivity of ROI two with the contralateral insula in the sucrose condition; these findings were also absent in the sucralose condition.
Author Conclusion:
  • Limitations as cited by authors:
    • Recruited women only and the response patterns may be different in men
    • Method of setting seed ROIs and assessing brain activation
  • The results indicate that:
    • Both sucrose and sucralose activate functionally connected primary taste pathways
    • Taste pleasantness predicts left insula response
    • Sucrose elicits a stronger brain response in the anterior insula, frontal operculum, striatum and anterior cingulate, compared to sucralose
    • Only sucrose, but not sucralose, stimulation engages dopaminergic midbrain areas in relation to the behavioral pleasantness response
    • Thus, brain response distinguishes the caloric from the non-caloric sweetener, although the conscious mind could not
    • This could have important implications on how effective artificial sweeteners are in their ability to substitute sugar intake.
Funding Source:
Other: funding source not given
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) N/A
  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) N/A
 
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? N/A
  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? ???
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%.) 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? N/A
  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? N/A
  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? N/A
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? N/A
  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