Scientists have long known that the brain sends signals to the gut, a process that reveals why stress, for example, can express itself through gastrointestinal symptoms. But it wasn’t until 2013, when researchers at the UCLA uncovered the first evidence that the signal can go the other way as well: from gut to brain.
By studying a group of women who regularly ate yogurt — and with it, the beneficial bacteria known as probiotics — they found that ingested bacteria in food can affect human brain function, effectively altering the way the brain responds to the environment. Specifically, the researchers found that the bacteria in yogurt may help relieve anxiety and stress by reducing activity in the insula, the region of the brain responsible for emotion.
"Many of us have a container of yogurt in our refrigerator that we may eat for enjoyment, for calcium or because we think it might help our health in other ways," said Kirsten Tillisch, an associate professor of medicine in the digestive diseases division at UCLA's David Geffen School of Medicine and lead author of the study. “When we consider the implications of this work, the old sayings 'you are what you eat' and 'gut feelings' take on new meaning."
The study is just one of many that comprise a growing body of research examining how gut flora, and the fermented foods that contain it, such as yogurt, impacts mood. Since 2008, when the U.S. National Institutes of Health launched the Human Microbiome Project, a five-year initiative to identify and characterize the microorganisms in both healthy and diseased humans, “the profound appreciation for the influence of such organisms has grown rapidly with each passing year,” writes Peter Andrey Smith in a New York Times Magazine article in June.
These helpful bacteria like probiotics do a lot for us, from extracting energy from the fermentation of undigested carbohydrates and increasing the growth of intestinal epithelial cells to synthesizing vitamins and suppressing the growth of pathogens.
Now a new study recently published in the journal Food Research International indicates that there may be other, completely different reasons why yogurt has the power to make us happy, and it has to do with the way expectation impacts mood and possibly even scent.
Conducted by a team of European researchers from Finland, Austria and the Netherlands, the study found that eating vanilla yogurt made people feel happy. Specifically, eating vanilla yogurt resulted in the study’s participants projecting more positive emotions than when they ate other flavors. Additionally, yogurts with less fat gave people a stronger positive emotional response, while yogurts with different fruits did not have much difference in their effect on emotions.
The researchers also found that liking or being familiar with a product had no effect on a person’s emotion. But most tellingly, what did affect mood was how they felt after eating the yogurt compared to what they expected to feel before eating it. In other words, their moods were influenced by their expectation — either being pleasantly surprised or disappointed after eating the food in question.
“We were looking for a valid, quick and not too expensive and time-consuming method to measure the emotions or mood changes evoked by food,” said Jozina Mojet from Food & Biobased Research in the Netherlands, lead author of the study. “This sort of implicit method can reveal the complex interactions between the different factors involved in a situation, which, based on his or her memory and expectations, is given meaning by the person under investigation.”
In addition, the strong positive emotional response elicited by eating vanilla yogurt supports earlier evidence that “a subtle vanilla scent in places like hospital waiting rooms can reduce aggression and encourage relationships among patients and between patients and staff,” according to the study’s press release.
To determine the effect of different yogurts on mood, the researchers exposed 24 subjects to a pair of yogurts of the same brand and marketed in the same way, but with different flavors or fat content. They used various analytical methods in the study, including tracking the subjects’ eye movements as they looked at the packaging, reading their faces while they ate the yogurt and a mood-based autobiographical reaction time test.
Notably, the researchers also used a new emotive projection test (EPT), in which study participants were shown photographs of other people and asked to rate them on six positive and six negative traits. “The idea behind the test is that people project their emotions onto their perception of others, so their judgment of others can indicate their own mood,” writes Lucy Goodchild van Hilten, senior marketing communications manager for life sciences at Elsevier, the publisher of Food Research International.
“We were surprised to find that by measuring emotions, we could get information about products independent from whether people like them,” said Jozina Mojet, lead author of the study. "This kind of information could be very valuable to product manufacturers, giving them a glimpse into how we subconsciously respond to a product.”
The study supports the findings of an earlier study by researchers at University College London that lower expectations lead to a greater level of happiness.
“It is often said that you will be happier if your expectations are lower,” said Robb Rutledge, the study’s lead author. “We find that there is some truth to this — lower expectations make it more likely that an outcome will exceed those expectations and have a positive impact on happiness.”
‘Our computational model suggests momentary happiness is a state that reflects not how well things are going but instead whether things are goingbetter than expected,” write the study’s authors.
Could eating yogurt and lowering expectations help to combat depression? While more research is needed, these studies suggest the answer is yes. In the meantime, for a quck and easy mood booster that’s also safe and healthy, try some vanilla yogurt. And try not to expect too much out of it.