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Psychology researchers at Yale and Arizona State Universities, who'd been inspired by the power of beliefs and expectations in affecting other physiological processes, set out to test the connection between a person's mind-set and how full they felt. However, they chose to measure satiety not by asking people, but by the less-subjective mechanism of analyzing their subjects' bodies for spikes and dips in the gut peptide ghrelin. "A key function of ghrelin is that it directly influences metabolism," study author Alia Crum of Yale wrote in an email. "Low levels speed up the burning of calories; high levels slow the burning of calories."

In a test that sounds a little like a modified infomercial, the researchers asked participants on two separate occasions to drink a 380-calorie milk shake. During one session, the label of the drink featured a tantalizing illustration of an ice cream treat, and the nutrition facts showed sky-high fat and calorie contents. In the other session, the label presented the shake as a "sensible" diet aid, with 0 percent fat, no added sugar and only 140 calories. The participants were unaware that the beverages were identical. During each taste test, they submitted blood samples that were analyzed for ghrelin levels.

When participants in the study drank the shake that they believed to be a calorie-packed treat, their ghrelin levels showed a significant and steep decline. But when they drank the "sensible" shake with the diet-friendly label, their ghrelin levels were flat or slightly increased. Consuming the shake in a mind-set of sensibility seemed to dampen the effect of ghrelin and compromise the body's ability to metabolize those nutrients, which is what can lead to an increase in appetite.

This could explain why foods we perceive as "diet" choices often seem less satisfying than foods that we recognize as sinful or decadent. Our dutifully sensible mind-set could cause ghrelin levels to be suppressed, which would keep us from feeling full and also from efficiently burning the calories. Crum says that this could even compromise our decision to choose the low-calorie option, because we could end up eating more of it, or choosing something even more unhealthy later that day.

The study, which was published last month in the journal Health Psychology, shows that the body is easily fooled by the mind, but how do we trick our own minds? It's not like we can slap a label for "Asiago Cheese Straws" on our bag of carrot sticks and expect our ghrelin levels not to catch on.

"I think the most important message from this study is for consumers to be aware of the mind-set that they are in while they are eating, and especially the mind-set that individuals seem to automatically adopt when trying to maintain or loose weight," writes Crum. "The mind-set of 'sensibility' or 'restraint'—no matter what we're eating—might be compromising our body's physiological response, counteracting our hard work at dieting. People should still work to eat healthy, but do so in a mind-set of indulgence." 

Crum suggests the following approach: When eating a chef salad, don't concentrate on the fact that iceberg lettuce is mostly water or that the reason you ordered it was because it seemed less damning than the steak frites. Choose instead to focus on "the indulgent aspects": the creaminess of the cheese, the way a small amount of dressing can pack a lot of flavor, the crunch of the sunflower seeds, the cold snap of the greens. Make healthy options, but find the pleasurable reasons to do so.

In other words, look for the milk shake in every meal. 

Keep reading:

7 Ways to Eat Mindfully

The Perfume Diet: The Surprising Joys of Sensual Indulgences

The Importance of Mindful Eating