"Stress signals danger and should make us detect [tastes like] bitter more strongly," Epel says. And this is exactly what happened in the study.
Participants in the study experienced a stronger sensitivity to bitter, sweet and sour tastes after watching emotional videos with storylines that were both happy and sad. In fact, their sensitivities to these tastes were heightened by about 15 percent.
But, at the same time, participants' ability to distinguish levels of fat "got much worse," according to researcher Paul Breslin of the Department of Nutritional Sciences at Rutgers University, who co-authored the study.
"It was a surprise," Breslin says, that perceptions of fat moved in the opposite direction.
It turns out, Breslin says, that his findings fit with a body of evidence that suggests that people who are mildly depressed and who have elevated body weight may have lower sensitivity to fat.
So, it's possible that if "they don't know the fat is there, and eat it, they may be inadvertently eating more fat," says Breslin. "That's sort of the concern here."
The research was carried out in Germany at the University of Wurzburg. Lead author Petra Platte, a psychologist by training, recruited participants to taste samples of a creamy drink that contained varying levels of fat.
At the start of the study, the participants were all feeling a little blue or anxious. Researchers were able to assess the emotional status of the participants by having them complete a 21-question survey, called the Beck Depression Inventory.
Then, the participants were asked to watch video clips. There was a feel-good, happy video of a man bringing flowers to a woman. There was also a sad clip in which a son watches his father die. Both of the videos were designed to elicit an emotional response.
In addition, there was a third video — a boring, unemotional workplace training clip. The participants who watched this unemotional clip did not lose the ability to gauge levels of fat.
So, it seems to be that it's an emotional reaction, when folks are already a little blue, that causes people to lose the ability to tell high fat from low. The study is published in the journal PLOS One.