Depression poses increasing public health challenges, and alternative dietary strategies are gaining attention for their potential therapeutic effects. This study evaluates a natural ingredient-based formula powder (FP) for its antidepressant effects in a chronic unpredictable mild stress (CUMS) mouse model under both a standard diet and high-fat high-sugar diet (HFHSD) conditions. Behavioral tests demonstrated that FP significantly reduced immobility time in the forced swimming test and tail suspension test, and improved anxiety-like behavior in the open field test, particularly by increasing the central zone activity in mice fed a standard diet. FP supplementation also mitigated CUMS- and HFHSD-induced organ damage, as indicated by increased small intestine and colon coefficients. At the molecular level, FP downregulated the expression of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6) and upregulated brain-derived neurotrophic factor (BDNF) and tryptophan hydroxylase-2 (TPH2) in the hippocampus and colon. These findings suggest that FP exerts antidepressant-like effects by alleviating neuroinflammation and supporting the gut-brain axis, offering a promising functional food approach for managing depression.