- Click here for explanation of classification scheme.

• To measure both changes in flavor evaluation and intake following flavor-MSG pairings
• To explore whether a novel savory flavor-conditioned stimulus acquired MSG-like flavor properties following repeated pairings of the flavor CS and a MSG flavor element.

Previously completed a general recruitment questionnaire which included questions from the Three Factor Eating Questionnaire (TFEQ).

• Those scoring more than six on the TFEQ restraint scale, because some studies have suggested that highly restrained individuals may be insensitive to flavor-based learning
• Allergy or an aversion to any of the foods on the ingredient list
• Diabetic
• Suffered from an eating disorder.

Recruitment

Recruited from staff and volunteers at the University of Sussex.

Design

Randomized controlled trial to contrast changes in voluntary consumption, hedonic and sensory evaluations of the flavor of a target savory soup on two test days before and after four training days where the soup was either consumed either unaltered (exposure to control condition) or with its flavor enhanced by the addition of 0.5% of MSG (MSG experimental condition).

Blinding Used

Subjects were blinded as to which training condition group (control group with nothing added or group with 0.5% MSG added) they were randomized.

Intervention

• Participants visited the Ingestive Behavior Unit on seven non-consecutive days
• On all seven days, participants were required to eat nothing and drink only water from 11:00 p.m. the previous evening and to report to the Unit at a pre-assigned time between 8:30 and 10:00 a.m. for breakfast
• Breakfast consisted of 60g cereal (Crunchy Nut Cornflakes, Kelloggs brand) along with 160g of semi-skimmed milk and 200g of orange juice (total 1,682kJ)
• Once breakfast was complete, participants were free to leave the Unit and were required to return three hours later, having consumed only water, for the main test session.

Day One: Practice session (participants not informed it was practice):

• Participants consumed a different soup than the test soup to allow them to become familiar with the software and prevent exclusion due to participant error.

Days Two and Seven: Test days (the Pre- and Post-training sessions):

• Participants were taken to a test cubicle and followed on-screen appetite and mood ratings
• They were served a bowl of the test soup, which they evaluated for hedonic and sensory properties and then consumed it ad libitum
• Participants were interrupted automatically by the SIPM (Sussex Ingestion Pattern Monitors) system after consumption of every 50g of soup and asked to rate hunger, fullness and thirst
• Additional bowls of soup (served 60° to 65°C) were provided after every 150g consumed until the participants had consumed as much as they liked, at which point the mood and appetite were re-rated
• Once ratings were complete, participants were free to leave on the pre-training day, but completed a brief structured debriefing. They had their height and weight measured in light clothing before being paid on the final (post-training) session.

Days Three to Six: training sessions:

• Participants were served a fixed quantity (200g) of soup, and were instructed to consume all of this (they were not able to eat ad libitum)
• The only ratings collected on training days were those before the soup was served, when soup was first tasted and when the meal was complete (no interruptions in eating to make additional ratings).

Statistical Analysis

• T-tests were used to determine any differences in hedonic or sensory evaluation between groups. This data was converted into change scores by subtracting the equivalent pre-training data, and these change data were then contrasted between training conditions using T-tests.
• Intake data at pre- and post-training were contrasted by two-way ANOVA, with session [(pre- or post-training within-subject and condition (MSG or control factors: between subject)]
• Hunger ratings at the start and end of soup intake at pre- and post-training were contrasted by three-way ANOVA, with session and time of rating within-subject and condition between-subject
• Change in hunger following initial tasting of the soup was calculated at pre- and post-training by subtracting rated hunger before soup was presented from rated hunger once the soup had been tasted as a test of the appetizing effect of the soup flavor. These changes were then contrasted between two training conditions at the two test sessions using mixed two-way ANOVA.
• Hedonic and sensory evaluations of the soup during training were contrasted between conditions across the four training sessions using two-way mixed ANOVA
• Hunger and fullness ratings at the start and end of soup ingestion were also contrasted between conditions and training sessions using three-way ANOVA, with condition between-subjects and time (start or end of meal) and session (pre- or post) within-subjects.

Timing of Measurements

• Seven non-consecutive days
• On all seven days, participants reported to the Unit at a pre-assigned time between 8:30 and 10:00 a.m. for breakfast. They returned for soup three hours later.

Dependent Variables

• Soup intake was measured using SIPM
  • SIPM system consisted of a concealed digital balance connected via a serial line to an Apple G3 computer, custom programmed using Future Basic II to read the balance weight on stability to an accuracy of 0.1g, at two-second intervals during feeding bouts
• Change in hedonic evaluations and change in sensory evaluations were measured using digital Visual Analog Scales (VAS) presented on the SIPM before and after eating.  

Independent Variables

Soups:

• Proprietary brand low-energy soup (Organic Soup in a Mug Leek and Potato flavor) combined with 200g boiling water
• Both soups were served in white ceramic soup bowls at a temperature of 60° to 65°C
  • Control soup: Fixed with 200g boiling water and was unaltered
  • MSG condition: Added 0.5% w/w MSG.

Control Variables

Practice and training days were used to get participants used to the software and prevent exclusion due to error.

Initial N

32 volunteers (27 women and five men).

	MSG Group	Control Group
Gender	13 women Three men	14 women Two men

 

Age

	MSG Group	Control Group
Age	22.3±2.2 years	24.9±2.3years	T (30)=0.83, NS

 

Anthropometrics

	MSG Group	Control Group
BMI	21.4±0.3	22.1±0.5	T (30)=1.17, NS

Location

University of Sussex.

Key Findings

• The change in pleasantness of the soup between post- and pre-training sessions differed significantly between training conditions [T(30)=2.85, P=0.008], with liking increasing in the condition which had added MSG during the intervening training sessions, but decreasing in the control condition
• The amount of soup consumed at pre- and post-training sessions depended on an interaction between condition and session [F(1,30)=6.02, P=002]
• The change in intake between pre- and post-training sessions differed significantly between conditions [T(30)=2.45, P<0.05), with intake increasing after training in the MSG condition but tending to decrease in the control condition
•  There was a large effect of time of rating (before or after the meal): [F(1,30)=25.23, P<0.001]
• There was a marginal interaction between session and time [F(1,30)=4.05, P=0.053], with a tendency for hunger to decrease less after eating at the post- compared with pre-training sessions in both conditions despite greater intake in the condition, which had MSG added during training
• Analysis of the changes in hunger showed a significant interaction of condition and time of rating [F(1,30)=4.30, P=0.047]
• Tasting the soup caused similar, small increases in hunger in both conditions during the pre-training session, but there was a marked increase in appetite after tasting the soup in the condition where MSG was added during training, which was significantly greater than that in the control condition [F(1,29)=6.64, P=0.015], at the post-training session. 

Other Findings

• Analysis of pleasantness and savory across the four training trials confirmed:
  • Pleasantness ratings differed significantly between conditions across the four training sessions [F(1,30)=10.02, P=0.004], with higher ratings in the MSG condition than in the Control condition
  • Addition of MSG significantly increased the savory quality of the soup ([F(1, 30)=5.87, p=0.022]
• Analysis of hunger and fullness and the beginning and end of the four training sessions showed:
  • Overall hunger was less [F(1,30)=50.48, P<0.001], after consuming the soup
• Correlational analysis showed:
  • Intake was positively correlated with rated soup pleasantness both at pre-training [R(32)=0.48, P=0.006] and at post-training [R(32)=0.50, P=0.004]
    •  This effect was still significant when the training condition was parceled out [pre-training R(29)=0.48, P=0.007; post-training R(29)=0.45, P=0.011]
  • Rated savoriness correlated with pleasantness [Pre-test r(32)=0.36, P=0.043): Post-test R(32)=0.41, P=0.02]
  • Rated pleasantness tended to be positively correlated with intake in both groups, and the restricted power in these analyses may have masked these effects
  • The only significant correlation for sensory quality was a negative correlation between changes in ratings of bitter and sour in the Control group and a positive correlation between changes in ratings of sour and salty in the MSG-paired group.

This study provides further evidence that liking for savory flavors can be enhanced by association with MSG, but whether these changes reflect a sensory of post-ingestive effect of MSG requires further substantiation.

Government:

UK Biotechnology and Biosciences Research Council (BBSRC)

• Note: Author states that the sample size limited the scope of the analyses and other relationships may have been significant if a larger sample had been tested
• Although there is a Discussion of Findings section, it does not appear to list any limitations. It merely compares the results of this study to several others.