This study evaluated the anti-inflammatory effects, protection of gut barrier integrity, and stimulation of phagocytosis in peripheral cells of a nutritional supplement based on a synergistic combination of yeast-based ingredients with a unique 1,3/1,6-glucan complex and a consortium of postbiotic Saccharomyces cerevisiae rich in selenium and zinc. The anti-inflammatory effect in Caco-2 cells in the presence and absence of a pro-inflammatory challenge (tumour necrosis factor alpha [TNF-α]/interferon gamma [IFN-ɣ]) showed statistically significant reductions of IFN-ɣ induced protein-10 (IP-10), and monocyte chemoattractant protein-1 (MCP-1) levels vs. controls (p < 0.001). Disruption of the gut integrity in the presence or absence of Escherichia coli (ETEC H10407) showed transepithelial electrical resistance (TEER) values higher in the ABB C1® group after 6 hours of testing. Spontaneous build-up of the gut epithelium monolayer over 22 days was also greater in the ABB C1® condition vs. a negative control. ABB C1® showed a significantly higher capacity to stimulate phagocytosis as compared with controls of algae β-1,3-glucan and yeast β-1,3/1,6 glucan (p < 0.001). This study supports the mechanism of action by which ABB C1® may improve the immune response and be useful to prevent infection and allergy in clinical practice.