Whole dietary interventions may reduce symptoms of depression/anxiety (1), but adherence is difficult. Single-food interventions, like almonds, may enable improved adherence and contain micronutrients associated with cognitive benefits and have a prebiotic effect on the gut microbiome (2). This randomised controlled trial assessed the effects of whole almonds on mental and gut health in adults with mild to moderate depression/anxiety.

Adults 18-45 years with Patient Health Questionnaire Anxiety and Depression (PHQ- ADS) (3) scores of 10-29 were randomised to 56g/day whole almonds (intervention) or two iso-caloric muffins/day (control) for 12 weeks. Symptoms of depression/anxiety (primary outcome) were assessed via the PHQ-ADS. Mental health and gastrointestinal symptoms were measured using validated questionnaires. Faecal samples were analysed for short- chain fatty acids via gas-chromatography, study measures were collected at week 0 (Baseline) and week 12 (Endpoint).

Eighty-four participants were randomised (mean age 25 years, BMI 23 kg/m2, 76% female, 46% white ethnicity). Among those who completed mental health and gastrointestinal symptom assessments (n = 81), almond consumption did not significantly affect depression and anxiety symptoms (p = 0.42), mental wellbeing (p = 0.98), or stool frequency (p = 0.32). However, functional impairment was significantly improved in the almond group compared to control (p = 0.05), and participants reported significantly fewer hard stools (p < 0.001). P-values for mental health measures were calculated using linear mixed models. P-values for stool-related outcomes were calculated using a linear regression with baseline values as a covariate.

Short-chain fatty acid (SCFA) concentrations were analysed in a subset of participants who provided faecal samples (n = 64; 31 in the almond group and 33 in the control group). There were no significant between-group differences in faecal SCFA concentrations, including total SCFAs (p = 0.51), acetic (p = 0.60), propionic (p = 0.47), butyric (p = 0.60), iso-butyric (p = 0.84), iso-valeric (p = 0.84), or valeric acid (p = 0.80). p-values were calculated using ANCOVA with baseline values as a covariate.

While almonds did not significantly reduce symptoms of depression/anxiety or the majority of mental health outcomes, they improved functional impairment and reduced reports of hard stools, suggesting potential benefits for mental and gut health. Microbiome analyses are ongoing to investigate potential markers related to the gut-brain axis. Future trials should assess whether singular food interventions have efficacy in severely depressed/anxious populations.