A pilot study involving 18 sedentary individuals aged 65 and older who had mild depressive symptoms found that consuming blueberries for three months was linked to more stable mood changes and slight changes in the bacteria in their intestines. The study, published in 2026 in The Journal of Nutrition, Health and Aging, aimed to explore how diet might affect the gut-brain axis, a relatively under-researched area of health. The gut-brain axis refers to the communication between the digestive system and the brain, and scientists are increasingly interested in how changes in the gut can influence mental health. The research team, from Hebrew SeniorLife, an organization affiliated with Harvard Medical School, focused on blueberries, a widely consumed food. Participants took 48 grams of freeze-dried blueberry powder every day, which is roughly equivalent to two cups of fresh blueberries. This amount provided 11 grams of fiber, including about 8 grams of additional fiber, which is nearly 30 percent of the recommended daily intake. The study used a technique called metagenomic sequencing to examine the genetic material of the bacteria in the participants’ intestines. Researchers also looked for specific substances, or metabolites, produced by these bacteria, such as butyrate and propionate, which are known to have beneficial effects on the body. The researchers were particularly interested in the potential benefits of fiber and anthocyanins, which are pigments found in blueberries that have antioxidant properties. These compounds may support gut health and, in turn, influence mood and brain function. However, the researchers emphasized that the results of the study are still very preliminary and do not yet provide enough evidence to support a claim that blueberries have an antidepressant effect. They noted that further research with larger groups and longer study periods is needed to confirm these findings. The study adds to the growing body of research on the connection between diet, gut health, and mental well-being. While the results are encouraging, they highlight the need for more comprehensive studies before any dietary recommendations can be made for mental health conditions. The researchers hope that their work will inspire future investigations into how specific foods might support both physical and psychological health in older adults.