Researchers have uncovered a gut-diet link to postpartum depression, finding that eating a diet of soy, fermented foods, and seaweed may nurture beneficial gut bacteria and protect mothers’ mental health.
With the link between the gut microbiome and mental health now fairly well established, scientists have begun looking at how promoting a healthy microbiome can improve conditions such as depression in real-life scenarios.
A new study led by Kyoto University has investigated how gut bacteria and diet are linked to postpartum depression in Japanese mothers.
“Our investigation was driven by the need to better understand how intestinal microbiota, physical condition, and dietary habits relate to maternal mood, even among mothers not clinically diagnosed with mental illness,” said Michiko Matsunaga, an associate professor in developmental psychology and neuroscience at Kyoto University, and the study’s lead and co-corresponding author.
Globally, the prevalence of postpartum depression (PPD), the onset of depressive episodes after childbirth, is estimated to be around 10% to 20%. Symptoms can include an unstable mood, loss of interest, feelings of guilt, sleep disturbances and disorders, and changes in appetite. PPD can develop at any time within the first year after the birth of a child and last for years. For Japanese women, particularly, cultural factors such as stigma, reluctance to seek outside help, and a preference for independence can deter women from seeking mental health treatment.
The researchers recruited 344 mothers of children up to age four, none of whom had diagnosed psychiatric or physical illnesses. The severity of participants’ depression was assessed using the Beck Depression Inventory-II (BDI-II), with scores of 20 or above considered high risk for depression. Mothers also reported on their sleep quality and duration, and completed a multidimensional physical scale that covered factors such as fatigue, hormone balance, and circulation. Stool samples were analyzed using RNA sequencing to measure microbiota diversity and the abundance of specific bacteria.
Participants also reported how often they ate 18 categories of foods. Factor analysis revealed two dietary patterns among participants: a vegetable and meat diet (VMD), which consisted of lots of vegetables, meat and fish; and a soy and fermented food diet (SFD), which was high in soy, fermented foods, seaweed, mushrooms, and fruits.
About 14% of mothers scored in the high-depression range despite being considered “healthy”. Lower gut microbiota diversity was associated with higher depression scores. Specific butyrate-producing bacteria – beneficial gut bacteria that ferment dietary fibers to produce butyrate, a short-chain fatty acid (SCFA) – were less abundant in mothers with more depressive symptoms. These bacteria are known to improve gut and immune health.
From a physical perspective, depressed mothers reported poorer sleep quality and worse overall physical condition. However, the researchers found that mothers who ate the SFD had lower depression scores, better physical condition, and healthier gut bacteria. The VMD pattern was linked to some physical health benefits, but not to lower depression. Mothers with depression were also found to eat less yogurt, dairy, and pickled vegetables than those with lower depression scores.
“These findings deepen our appreciation for the richness of traditional Japanese dietary culture and its potential mental health benefits,” said Masako Myowa, PhD, the study’s other corresponding author.
One of the study’s biggest limitations is that its cross-sectional design can show associations but not cause-and-effect. Additionally, food intake was self-reported, with only 18 food categories; there were no details on whether the foods were processed or fresh, nor on the types of meat and fish eaten, for example. Factors like marital status, exercise, or family mental health history were not included. Results may reflect unique aspects of Japanese diets and may not fully apply elsewhere.
Despite these limitations, the study does raise an interesting consideration: diet as prevention. Eating more soy, fermented foods, seaweed, mushrooms, and vegetables may help reduce the risk of postnatal depression, partly by supporting gut bacteria that produce beneficial fatty acids. The study highlights the importance of the gut-brain axis in maternal mental health, suggesting non-drug interventions such as dietary changes or probiotics could support long-term well-being.
The researchers plan to conduct further studies to examine whether targeted dietary changes can improve both gut bacteria and mental health in postpartum women.
“I find it fascinating that this integrated perspective may help us better understand emotional states and develop new, holistic approaches to mental health support,” Matsunaga said.
The study was published in the journal PNAS Nexus.
Source: Kyoto University
