You Are What You (Think) You Eat

New research reveals why food labeled “healthy” is unsatisfying.
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New research reveals why food labeled “healthy” is unsatisfying.

After eating food marketed as “low-fat” or “guilt-free,” do you still feel hungry? If so, don’t blame the food: Blame the label.

A key hormone associated with the feeling of satiety responds far more dramatically when people think they are consuming an indulgent treat. That’s the conclusion of newly published research from Yale University, which finds what we tell ourselves about the food we eat affects the point at which we start feeling full.

The study, tastily titled "Mind Over Milkshakes" has weighty implications for the campaign against obesity. Its findings suggest labeling foods as healthy may be counterproductive, since doing so apparently produces an unwanted and unhelpful physical response.

Writing in the journal Health Psychology, a research team led by Yale psychologist Alia Crum describe an experiment featuring 46 participants. A reasonably diverse group, its subjects ranged in age from 18 to 35, and in body size from normal to overweight. They participated in two 2.5-hour sessions, which took place precisely one week apart.

“At the first session, participants were told that that the metabolic kitchen at the Yale Center for Clinical Investigation was working on designing two different milkshakes with different nutrient content, and that they would taste one milkshake in the first week and another milkshake the following week,” the researchers write. “They were told the goal of the study was to evaluate whether the milkshakes tasted similar, and to examine the body’s reaction to the different nutrients (high versus low fat, high versus low sugar, etc.).

“Unknown to the participants, however, the contents of the two milkshakes were identical. However, the labels depicting these beverages differed.”

During one of the two sessions, participants taste-tested a shake described as high fat and high calorie; the label called featured the word “indulgence” and the slogan “decadence you deserve.” During the other session, the shake was described as low fat and low calorie; the label boasted about “guilt-free satisfaction.”

Blood samples were drawn from each participant 20, 60 and 90 minutes into each session. “During the first interval (between 20 and 60 minutes), participants were asked to view and rate the label of the shake,” Crum and her colleagues note. “During the second interval (between 60 and 90minutes), participants were asked to drink and rate the milkshake.”

Via the blood samples, the researchers tested the participants’ level of ghrelin, a gut peptide that has been called “the hunger hormone.”

“When energy intake is low, or the stomach is empty, ghrelin is secreted from the endocrine cells of the stomach and transported in the bloodstream to the brain, where it binds with receptors … to produce the sensation of hunger,” the researchers write. “As energy intake increases and nutrients are detected in the gastrointestinal tract, ghrelin levels are suppressed, thereby signaling to the brain” to produce a feeling of satiety.

At least, that’s the way it’s supposed to work. This study suggests our expectations can short-circuit this crucial process.

“When participants drank the indulgent shake, they had a significantly steeper decline in ghrelin than when they drank the (physically identical) sensible shake,” the researchers found. “(Their) level of ghrelin reflected a moderate level of physiological craving, followed by a significant level of physiological satiety.

“On the other hand, when drinking the shake in a sensible mindset, participants exhibited flat or slightly increased levels of ghrelin over the course of consumption, suggesting that, despite consuming the same nutrient contents, they were not physiologically satisfied.”

These results are “consistent with what one might observe if participants actually consumed beverages with different caloric counts,” the researchers note. “Participants’ satiety was consistent with what they believed they were consuming, rather than the actual nutritional value of what they consumed.”

Think of it as the evil twin of the placebo effect.

While much research remains to be done, these results suggest labeling food as “good for you” may produce a destructive backlash. The researchers are particularly troubled by the not-uncommon practice of putting health claims on the labels of not-particularly-healthy foods.

“This juxtaposition … may be especially dangerous,” they write. The misleading label may inhibit the onset of the feeling of fullness, prompting people to eat more of the unhealthy food.

"Perhaps if we can begin to approach even the healthiest foods with a mindset of indulgence,” Crum and her colleagues conclude, “we will experience the physiological satisfaction of having had our cake and eaten it, too.”

Of course, that would require a radical redefinition of a decadent dish. Anyone for a scrumptious serving of spinach?

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