Soy beans
Soy beans. Credit: Wikimedia Commons/Midori Reuters

A soy-rich diet could help reduce anxiety levels caused by certain household chemicals, scientists from North Carolina State University have found.

According to them, exposure to bisphenol A (BPA) results in high levels of anxiety by causing significant gene expression changes in a specific region of the brain called the amygdala. The chemical is used in a wide range of polycarbonate plastics and epoxy resins, such as some food containers.

"We knew that BPA could cause anxiety in a variety of species, and wanted to begin to understand why and how that happens," said Dr Heather Patisaul, an associate professor of biology at North Carolina State University.

The scientists' findings are based on a study of mice. The creatures were exposed to low doses of BPA during gestation, lactation (nursing) and through puberty. After puberty, one group of mice was fed only soy, and the other group was given a soy-free diet.

The study found that adolescent rats which consumed a soy-free diet exhibited significantly higher levels of anxiety. Adolescent rats which took a soy-rich diet did not exhibit anxiety. This suggested that a soy-rich diet may mitigate the effects of BPA.

Researchers also found for the first time gene changes within the brain associated with this elevated anxiety. They noticed certain gene expression changes in the amygdala, the brain region known to play a role in mediating responses to fear and stress.

According to them, two genes, estrogen receptor beta and the melanocortin receptor 4, were affected. They say that the both genes are required for oxytocin release. Changes in oxytocin/vasopressin signaling pathways may underpin the behavioural changes. Oxytocin is a hormone and neurotransmitter that has been linked to social behaviour.

"Soy contains phytoestrogens that can also affect the endocrine system, which regulates hormones," Patisaul said. "It is not clear whether these phytoestrogens are what mitigate the effect of BPA, or if it is something else entirely. That's a question we're hoping to address in future research."