Mind Over Milkshakes
Running head: MIND OVER MILKSHAKES 2
MIND OVER MILKSHAKES 2
Mind Over Milkshakes:
Mindsets, Not Just Nutrients, Determine Ghrelin Response
Kristen Tomlinson
Florida International University
Mind Over Milkshakes
Summary:
Brownell, Corbin, Crum and Salovey (2011) designed a study to test the hypothesis of whether physiological satiation as measured by the gut peptide ghrelin may vary depending on the mindset in which one approaches consumption of food. The sample consisted of 46 participants from the New Haven Community in both on and off campus locations.
This study used an experimental research method because the independent variable is being manipulated and involves random assignment. There is only one main independent variable. It is the altered food labels that were used to isolate the effect of the mindset in the response to an experimental manipulation. They were scheduled for two, 2 1/2-hour sessions at the Yale Clinical Research Center Hospital Research Unit. The sessions were spread a week apart, one at 8:00 a.m. and the other at 8:20 a.m. after having an overnight fast. At the first session, the participants were told that the metabolic kitchen at the research center was working on designing two different milkshakes with different nutritional contents in them. They would taste one milkshake one week and another the following week. They were told the goal of this study is to determine whether the milkshakes taste the same and to examine the body’s reaction to the contents. This independent variable is evaluated to see how it affects the dependent variable, which is their ghrelin levels and how their body reacts to it as well as, the participants thoughts on if the milkshakes tasted good, whether it was healthy, and their feelings of hunger.
For the researcher to control how quick the participants consume the shake, they were instructed to drink the whole shake within the first 10 mins of this interval. They were all normal weight, they were asked to do an overnight fast before, so that all their ghrelin levels were around the same the next morning and they were all between the ages of 18-35. They were also screened for diabetes, pregnancy, allergies and a variety of other medical conditions.The procedure goes as follows: Participants were told they were participating in a study to see whether the milkshakes tasted similar and to examine how to the body will react to the different nutrients in the shakes. What they don’t know is that the two milkshakes are identical. To complete this study, the participants were scheduled for two, 2 ½- hour sessions at the Yale research center. At each session, an internal catheter was placed to draw blood and after a 20-minute rest, the first blood sample is drawn, followed by samples being taken at the 60- and 90-minute marks. During the first interval, participants were asked to rate the labels. Then during the second interval, they were asked to drink and rate the shake. The order of how the milkshakes were presented to the participants was counterbalanced so half received the sensi-shake in the first session and the other half received the indulgent shake in the first session.
To assess the effect of the degree of satiation and on the participants perception of healthiness and tastiness of the milkshakes, a mixed model analysis of variance (ANOVA) was conducted with shake type, restrained eating, and order were included in the model as factors to be used in the study (Crum et al., 2011, p. 427). The results of this study confirmed their hypothesis. When participants drank one of the shakes with an indulgent mindset, the levels of ghrelin were much lower than the participants who drank the sensi-shake, which suggests there is a relationship between satiation and craving. On the other hand, when participants drank the other shake (which was the sensi-shake) they showed a slight increase in their levels of ghrelin over the time of consumption. But they were not physiologically satiated. In this article, the authors noted that the participants rated the sensi-shake as much “healthier” than the indulgent. However, there are no significant differences in how the participants reported their feelings of hunger during the experiment which shows that there is no relationship between satiation and cravings.
Critique:
Overall this study was well designed by testing the hypothesis on whether the physiological satiation that is being measured by ghrelin, may vary depending on the mindsets of the participants when they consumed the milkshakes. The method of using the same shake for two groups of participants and the responses are very similar to the proven phenomenon of counterregulatory eating. Counterregulatory eating refers to a situation in which a person will eat more after having eaten something previously then after having eaten nothing at all. Therefore, the results of Brownell, Corbin, Crum, and Salovey (2011) makes sense because when people think they have consumed a high-calorie food they report as being full and eat less in response, whereas when people believe they have consumed a low-calorie food they report as still being hungry and eat more in response.
Based on the results, chances are that the participants pattern of ghrelin responses is consistent with what one might observe if they were to consume drinks with different caloric contents, so in that sense this study can be considered reliable (meaning it can be repeatable). Also, in the current sample of people, reliability of the restraint eating subscale was adequate. Validity is not as strong, though. Validity refers to whether the study is measuring what it is supposed to measure. When the participants drank the indulgent shake, they had a decline in their ghrelin responses than when they drank the sensible shake. Incorporating subsequent consumption is important for putting these findings in the context of the literature on restrained eating. Even though restrained eating was not a significant piece in the ghrelin responses in the study, research supports the fact that restrained eaters will respond differently to food and label cues than those who are not restraining their eating. In this study, the ghrelin profiles, were psychologically mediated and were dependent on the expectations of the milkshakes nutritional contents as opposed to the nutritional differences. However, the analyses of the measure of hunger, produced no interaction effects as a function of the shake, time, or restrained eating. So how can they measure whether subtle changes in the mindset associated with eating might affect the release of ghrelin in response to consumption if they want participants to fast overnight? I’m not sure that they were measuring their variables right. It did show that even though there were no significant differences to their hunger regardless of mindset after having consumed the milkshake, findings state that the psychological mindset of sensibility during consumption may dampen the effect of ghrelin. The ethics in this study is questionable. The sensible label manipulation may have elicited the mindset of restraint even in the participants that did not consistently report themselves as being restrained. By doing this could have caused negative results at the end of the study. Nonetheless, participants drank the indulgent shake and had a steeper decline in ghrelin than when they drank the sensible shake. Due to the nature of this research question, there is no other way to measure if changes in the mindset will influence the release the ghrelin in the body.
The method that they used for this study is better than the alternatives because they recruited a sample of random participants by putting up flyers around the community. They explained to the participants what the goal of the study was while also keeping information from them about what the study is about so that way the researches can manipulate the labels on the milkshakes. They also did a good job choosing the age range for the sample, as well as running a screening to test them for allergies, pregnancy and other medical conditions so they can make sure everything goes good with the study and they won’t have any major differences with the results. Clearly this method is a great way of exhibiting an experimental research study. Also, by using the restraint subscale allowed the researchers to have a stable factor structure across genders and weight categories.
Based on the results, in order to assess the label manipulation on the health and taste of the milkshake, a model analysis had to be used to interpret the data. For the healthiness, there was significant effect on the type of shake and no interaction effect for the restrained eating or the order in which the shakes were consumed. There were no effects on the tastiness of the shakes. Simple tests suggest that participants rated the sensible shake as being healthier than the indulgent shake. To test the effect of ghrelin and hunger, researchers assessed the data using a mixed-model with time, the type of shake, and order (session 1 and 2). The model did fail to interpret the data and effects of the order of the shakes. The participants did exhibit a steeper rise in ghrelin as well as a steep decline in hunger when they consumed the indulgent shake. Whereas, when they consumed the sensible shake, the levels of ghrelin exhibited as being flat or slightly increased over the course of consumption and were not physiologically satiated despite having the same nutritional contents. As for the measure of the hunger, the analyses produced no effects as a function of the shake, the time or the restrained eating. However, in this case the ghrelin profiles were psychologically mediated. Although the effect of psychologically mediated differences on long term alterations in weight and following consumption were not measured in this study, future research on the impact of this phenomenon on metabolic maintenance is justified. Increased ghrelin levels can cause an increase in body weight and fat gain because of the amount of caloric consumption. The flat ghrelin profiles that were shown when the participants consumed the sensible shake, may be placing them in a psychologically challenging state by showing an increase in appetite and a decrease in their metabolic rate.
Brief summary
Brownell, Corbin, Crum and Salovey (2011) designed a study to test the hypothesis of whether physiological satiation as measured by the gut peptide ghrelin may vary depending on the mindset in which one approaches consumption of food. On 2 occasions, a sample of 46 participants consumed a 380-calorie milkshake under the pretense of two milkshakes (indulgent and sensi-shake). Ghrelin was measured via IV blood samples at 3 time points: baseline, anticipatory and post consumption. During the first interval, researchers asked the participants to view and rate the (mislead) label of the milkshake. During the second interval, they were asked to drink and rate the shake. The mindset the participants had when they consumed the indulgent shake produced a steeper decline in ghrelin, whereas the mindset they had when they consumed the sensible shake was a flat ghrelin response. The satiety was consistent throughout with what they believed rather than the actual nutritional value. The authors concluded that the effect of food consumption on ghrelin may be psychologically mediated, and the mindset affects physiological responses to food.
References
Brownell, K.D., Corbin, W.R., Crum, A.J., & Salovey, P. (2011). Mind over milkshakes: Mindsets, not just nutrients, determine ghrelin response. Health Psychology, 30, 424-429. doi: 10.1037/a0023467