Think that bag of potato chips will make you happier than a healthy cup of yogurt? Think again. Eating yogurt has an emotional impact on your brain. Already known as a useful way to reduce stroke risk and improve digestion, yogurt may help people cope with mood, anxiety, stress and pain, according to researchers at the University of California, Los Angeles.

Evidence that bacteria eaten from food could directly impact brain function.

The essential ingredient, according to the researchers, is the living bacteria, known as probiotics, found in most forms of yogurt and also found within the body’s gut. Probiotic yogurt has already been shown to have beneficial effects for the human digestive system, such as helping treat diarrhea.

Now there is evidence that bacteria eaten from food could directly impact brain function.

The UCLA study included 36 women between the ages of 18 and 53 with a healthy body mass index (BMI). One group was given an eating regimen of probiotic yogurt twice a day for a month. Another group was given the same regimen with non-probiotic yogurt. A third group was given no dairy products at all.

All subjects were given a functional magnetic resonance imaging (fMRI) brain scan before and after their yogurt regimen. In addition, to get a picture of their emotional state, the women were given an emotional faces attention task, in which their brains were scanned while matching a series of emotional faces on a computer screen.

Women who ate the probiotic yogurt showed reduced brain activity in several critical regions, such as the somatosensory cortex and insular cortex, during the emotional task. The somatosensory cortex receives sensory information from all areas of the body and the insular cortex integrates sensory information from internal areas of the body such as the gut.

In contrast, women who ate non-probiotic yogurt or no dairy at all for a month showed either no change or an increase in brain activity in these regions.

In the non-emotional state, women who ate probiotic yogurt showed stronger neural connectivity between the periaqueductal grey – an area of the brain that responds to pain and emotion – to the prefrontal cortex, an area of the brain responsible for most decision making.

Women who did not eat probiotic yogurt showed enhanced connectivity between the periaqueductal grey and the emotion-related parts of the brain, such as insular cortex, somatosensory cortex and amygdala, leaving them more vulnerable to emotion. While the exact mechanisms behind the alterations in brain function are as yet unclear, the researchers suggest that bacteria in the gut may send molecular signals to the brain that change over time.

Dr. Emeran Mayer, the study’s senior author, explained that our diet can influence the way gut bacteria break down food. A Mediterranean diet rich in vegetables and fiber promotes the growth of healthy gut bacteria, while a diet loaded with fats and carbohydrates leads to a different set of gut bacteria that are less helpful to the human body.

“Now we know that [helpful gut bacteria] has an effect not only on metabolism but also affects brain function,” Mayer said.

The discovery that changes in the bacteria in the intestinal tract can affect the brain has significant implications and could point the way toward dietary or drug interventions to improve brain function.

Patients with irritable bowel syndrome (IBS) have imbalances in their gut bacteria and are often treated with probiotic substances, as well as peppermint oil and dietary fiber. In the future, the researchers hope to study a cohort of patients with IBS and other digestive disorders in an effort to identify the molecular signals that contribute to the shifts in brain responses induced by probiotic foods.

The study appears in the current online edition of the journal, Gastroenterology.