Mind Over Milkshakes: Detailed Notes

Mind Over Milkshakes: Mindsets, Not Just Nutrients, Determine Ghrelin Response

Objective

The study aimed to determine if physiological satiation, measured by ghrelin levels, varies depending on the mindset towards food consumption.

Methods

• Participants: 46 participants were involved in the study.
• Procedure: Participants consumed a 380-calorie milkshake on two separate occasions.
  • They were misled to believe it was either a 620-calorie "indulgent" shake or a 140-calorie "sensible" shake.
• Measurements: Ghrelin levels were measured through intravenous blood samples at three intervals:
  • Baseline (20 min)
  • Anticipatory (60 min)
  • Post-consumption (90 min)
• During the first interval (20-60 min), participants viewed and rated the misleading label of the shake.
• During the second interval (60-90 min), they consumed and rated the milkshake.

Results

• Ghrelin Response:
  • The "indulgent" mindset led to a significantly steeper decline in ghrelin levels after consumption.
  • The "sensible" mindset resulted in a relatively flat ghrelin response.
• Satiety: Participants' satiety aligned with their beliefs about what they consumed, rather than the actual nutritional content.

Conclusions

• The impact of food consumption on ghrelin may be psychologically influenced.
• Mindset significantly affects physiological responses to food.

Keywords

Mindset, nutrition, ghrelin, hunger, product labeling

Introduction

• Mindset (thoughts, beliefs, and expectations) is a crucial component in health.
• Expectation to heal enhances medication effects.
• Interpretation of events influences the impact of stress and illness.
• Identifying housework as exercise elicits physiological benefits.
• Mind and body are interdependent.

Food Expectancies

• Mindset determines taste and preference.
• Examples:
  • Coke tastes better from a brand-name cup (McClure et al., 2004).
  • Strawberry yogurt and cheese spreads are less enjoyable when labeled "low-fat" (Wardle & Solomons, 1994).
  • Adding vinegar to beer as a "special ingredient" can improve taste ratings if the consumer is unaware of the vinegar (Lee, Frederick, & Ariely, 2006).
  • Perceived cost of wine affects the brain's pleasure center (Plassmann, O’Doherty, Shiv, & Rangel, 2008).

Food Labels and Perceptions

• Affect hunger and subsequent food consumption.
• People adjust eating based on perceived calorie intake.
• High calorie preload leads to greater fullness and less consumption.
• Low calorie preload leads to more hunger and increased consumption.
• Restrained eating can moderate these differences.
• Counterregulatory eating: Highly restrained participants eat more after perceiving a high calorie preload.

Ghrelin and Energy Balance

• Ghrelin is a gut peptide identified as an essential indicator of energy insufficiency.
• When energy intake is low, ghrelin is secreted, leading to hunger and motivating consumption.
• As energy intake increases, ghrelin levels are suppressed, reducing appetite and increasing satiety (Baynes, Dhillo, & Bloom, 2006; Murphy, Dhillo, & Bloom, 2006).
• Ghrelin levels should rise and fall in proportion to calories consumed for metabolic balance (Zigman & Elmquist, 2003).
• Complex communication exists between metabolic and neurological systems.
• Abnormalities in ghrelin signaling may be associated with weight gain and obesity (Cummings, 2006).
• Ghrelin administration promotes food intake and body weight gain (Theander-Carillo et al., 2006; Wren et al., 2001, as cited in Castaneda et al., 2010).

Current Study

• Investigated whether mindset influences ghrelin release in response to food consumption.
• Considers the moderating influence of restraint on eating behavior and satiety (Heatherton, Polivy, & Herman, 1989).
• Analyzed the influence of restrained eating on ghrelin response (Schur, Cummings, Callahan, & Foster-Schubert, 2008).

Method Details

• Participants: Recruited through flyers for a "Shake Tasting Study" at the Yale Center for Clinical Investigation.
  • Received $75 for two 2.5-hour sessions.
  • Ages 18-35, BMI in normal to overweight range (M = 22.5, SD = 4.04).
  • Prescreened for diabetes, pregnancy, chronic conditions, and food allergies.
  • Final Data: 46 participants (65% women, 78% student, 22% community member; 56% White, 12% African American, 11% Asian American, 10% Hispanic/Latino, 11% other).
• Design and Procedure:
  • Two 2.5-hour sessions, 1 week apart, at 8:00 a.m. or 8:20 a.m. after an overnight fast.
  • Participants were told the study evaluated whether two milkshakes with different nutrient contents tasted similar and examined the body’s reaction to nutrients (high vs. low fat/sugar).
  • Milkshakes were identical in content but had different labels: "indulgent" (high fat, high calorie) or "sensible" (low fat, low calorie).
  • An intravenous catheter was placed for blood drawing.
  • Blood samples were drawn at 20 min (baseline), 60 min (anticipatory), and 90 min (post-consumption).
  • Participants viewed and rated the label (20-60 min) and then consumed and rated the milkshake (60-90 min).
  • Shake consumption was to be completed within the first 10 minutes of the interval.
  • Order of milkshake presentation was counterbalanced.

Measures

• Ghrelin: Measured using a double antibody RIA (GHRT-89HK) with intra-assay variability of 4-10% and inter-assay variability of 4.8-12.8% (Millipore; St. Charles, MO).
  • Samples kept on ice, spun, and plasma stored at -70 °C until analysis.
  • Total blood collected: 90 ccs (45 ccs per visit).
• Taste Ratings: Participants commented on smell, appearance, taste, enjoyment, and healthiness via 100-mm visual analogue scales (0 = not at all, 100 = extremely).
• Hunger Ratings: Subjective feelings of hunger were rated 10 minutes before each ghrelin measurement using 100-mm visual analogue scales (0 = not at all, 100 = extremely).
• Restrained Eating: The Dutch Eating Behavior Questionnaire (DEBQ; Van Strien, Frijters, Bergers, & Defares, 1986) was used.
  • Only the restraint subscale was analyzed.
  • This scale assesses unidimensional restraint.
  • Reliability in the current sample: Cronbach’s α = .82. Restrained eating was dichotomized at the midpoint.

Results Details

• Perceived Healthiness and Tastiness: Mixed-model ANOVA was conducted with shake type (indulgent, sensi-shake), restrained eating (nonrestrained, restrained), and order (Session 1, Session 2) as factors.
  • Perceived Healthiness: Significant main effect for type of shake, F(1, 89) = 42.50, p < .01, \eta^2 = .33. Sensi-shake was rated as healthier than the indulgent shake, t(44) = 15.61, p < .01.
  • Perceived Tastiness: No significant main or interaction effects.
• Ghrelin and Hunger: Mixed-model ANOVA with time (baseline, anticipatory, postconsumption), shake type, & order.
  • No significant main effects or interactions involving order, so data was collapsed over order.
  • 2 (shake type) x 3 (time) repeated-measures GLM with restrained eating.
  • Quadratic shake x time interaction effect expected.
  • Ghrelin: Reliable quadratic effect, F(1, 44) = 4.36, p < .04, \eta^2 = .091. Steeper rise in ghrelin in anticipation of the indulgent shake, followed by a steeper reduction after consumption.
  • Indulgent mindset: Moderate physiological craving followed by significant satiety.
  • Sensible mindset: Flat or slightly increased ghrelin levels.
  • No significant interaction or between-subjects effect of restrained eating.
  • The primary driver of the quadratic effect was the response to consuming the shake, F(1, 44) = 5.75, p < .02, \eta^2 = .12.
  • The anticipation effect was not significant, F(1, 44) = 0.94, p = .34, \eta^2 = .02.
  • Hunger: No significant main or interaction effects.

Discussion

• Participants had a steeper decline in ghrelin after consuming the indulgent shake compared to the sensible shake.
• Ghrelin response was dependent on perceived expectancies rather than objective nutritional differences.
• Psychological mindset of sensibility while eating may dampen the effect of ghrelin.
• Elevated ghrelin levels can cause increased body weight and fat gain (Murphy et al., 2006; Zigman & Elmquist, 2003).
• Ghrelin antagonists can have the opposite effect (Castaneda et al., 2010).
• Flat ghrelin profiles in response to the sensible shake may lead to increased appetite and decreased metabolism.

Limitations and Future Research

• No significant differences in subjective hunger were found, possibly due to measurement timing or method.
• Additional research is needed to understand the relationship between ghrelin levels, subjective hunger, and subsequent consumption.
• Future studies should incorporate subsequent consumption and consider restrained eating.
• Label manipulation is common, and inaccurate or misleading health claims may be dangerous.
• The juxtaposition of unhealthy nutrients with healthy proclamations might lead to inadequate ghrelin suppression.
• Mindset alterations have the potential to elicit a seemingly inappropriate sense of satiation.
• Further research is warranted to understand better how psychological factors influence the biological impact of food.