What believe about a food's ingredients may have a biological effect on our bodies above and beyond the actual nutrient content.
That is the conclusion from a study published in the journal Health Psychology, which was recently covered by Alix Spiegel at the NPR Health blog.
The authors conducted an experiment in which they fed the same 380 calorie milk shake to two different groups of subjects. The first group was lied to, and were told (via a label) that the shake was a "sensible" 140 calories. The second group was also lied to, but in the opposite manner: they were told (via a label) that the shake was an "indulgent" 620 calories.
The researchers measured the levels of a hormone, ghrelin, before during and after the label experiment. Ghrelin levels are particularly interesting to monitor because they regulate metabolism and help signal hunger or satiety. After eating a big meal, ghrelin levels fall, signalling us to stop eating. Eat a light meal, and ghrelin levels remain high, signaling us to eat more.
The authors found that people consuming the "indulgent" labeled shake experienced a significant increase in ghrelin just before consumption (in anticipation) and then a significant decline in ghrelin after consumption. The change, the authors argue, is consistent with that typically observed after eating a big meal. By contrast, the level of ghrelin was flat before and after eating the "sensible" shake. All this is in spite of the fact that the two shakes were exactly the same in every way except for the labels!
The authors were quoted as saying:
Labels are not just labels; they evoke a set of beliefs
and that labels might
actually affect the body's physiological processing of the nutrients that are consumed.
One way to interpret the results is to place them in the category with other "behavioral biases" in the behavioral economics literature: another piece of evidence that people do not behave rationally. I see it a bit differently. The results suggest a kind of "extra" rationality. Mind over matter. What we think might well trigger how our body responds. Marketers might influence what we think about foods, but we have some control over the process too.
Now, if I can just fool myself into believing that small lunch salad is actually one of the Carl's Jr. "Indulgent Salads", I'll feel fuller and lose more weight!
The study's sample size was small (N=46), probably because to measure ghrelin they had to insert an intravenous catheter to draw blood at repeated intervals. So one proceed with caution until more work of this sort is done. Still, very interesting nonetheless.