Let's review what we know about ghrelin. Identified in 1999, ghrelin is a hormone that sends information from the stomach to the brain.
When energy intake (i.e., nutrients, calories) is low or the stomach is empty, ghrelin is produced in the stomach and transported to the brain. There it binds with receptors to produce the sensation of hunger and motivate eating.
As energy intake increases and nutrients are detected in the gastrointestinal tract, ghrelin production slows, thus signaling to the brain to reduce appetite and increase feelings of satiety. This is part of the reason we're always told to eat slowly: it takes time for ghrelin production to be modulated with food intake, and time for ghrelin communication with the brain to take place, thus giving us the feeling of being full.
The power of the study presented today:
Crum, A., Corbin, W., Brownell, K., & Salovey, P. (2011). Mind over milkshakes: Mindsets, not just nutrients, determine ghrelin response. Health Psychology, 30 (4), 424-429 DOI: 10.1037/a0023467
is its simple elegance in examining the relationship of expectations of satiety on the production of ghrelin. Does one's perception via a package label affect the biological underpinnings of appetite?
Participants were brought to the research lab on 2 occasions a week apart. They were told that they would be testing 2 new shakes being developed at the lab, that they would be asked to drink and evaluate the shakes, and that blood samples would be taken to test their bodies' reactions to high and low fat and sugar content.
However, the shakes were different only in their labels . . . the contents of the containers were identical. One label read "Indulgence: Decadence you Deserve," with 620 calories, 30 grams of fat, and 56 grams of sugar. The other label read "Sensi-Shake: Guilt Free Satisfaction," with 140 calories, 0 grams of fat, and 20 grams of sugar.
Would the labels influence the participants' evaluation of the shakes? And would the expectation of what was being consumed change the production of ghrelin?
Perhaps not surprisingly, participants rated the the perceived "healthiness" of the Sensi-Shake significantly greater than that of the Indulgence shake. Remember, the only difference between the shakes was the label.
Further, there was no difference in ratings of taste between the 2 shakes. Nor was there a significant difference in the subjective feeling of hunger. These are powerful results in themselves. The labels did not influence the participants' perception of taste or feeling of fullness.
The researchers measured ghrelin levels 3 times: before the experiment began (baseline), after seeing the label but before consuming the shake (anticipatory), and after consuming the shake (postconsumption). When presented with the Indulgence shake, ghrelin levels rose significantly in anticipation and declined precipitously after consumption. When presented with the Sensi-Shake, ghrelin levels remained flat or rose moderately in anticipation and declined significantly after consumption.
Further statistical analysis revealed that the significant factor in these changes was the decline in ghrelin after consumption of the shake, not the anticipatory bump. And the ghrelin levels of those in the Indulgence mindset declined significantly more than the levels of those in the Sensi-Shake group.
The statistical power of the study is enhanced by the use of the same people on 2 occasions to consume the shakes. This reduces the variability between the 2 conditions and increases the statistical power of the analyses. For example, baseline ghrelin levels are likely to be very similar in each person from week to week.
In addition, there was a 1-week interval between consuming the shake in the Indulgence mindset and the one in the Sensi-Shake mindset. This interval reduces the chance that the participants would remember the first shake and directly compare the experience of the shakes.
The erroneous nutritional content of the label had a significant effect on the ghrelin response. So what of nutrition labels we encounter every day? The authors make a worrisome conclusion:
"A product may be labeled 'low-fat' (because it is lower in fat than a full fat option) but still be a high-fat food. A food product might be a good source of fiber but still have a sugar content that is exorbitantly high. This juxtaposition of unhealthy nutrients with healthy proclamations may be especially dangerous. Not only is the product itself unhealthy, but the mindset of sensibility might correspond to an inadequate suppression of ghrelin, regardless of the actual nutrient makeup."
The mind and the body . . . intimate partners at the most basic biochemical level.