The immune system requires an adequate supply of nutrients, although current dietary recommendations may not account for optimal immune function in healthy adults. Nutrient inadequacies due to the growing influence of the western diet pose a risk for immune dysfunction. This review aims to determine the beneficial effects of supplementing dietary fats, nutrients that modulate gut microbiota, and specific micronutrients on systemic immune functions (concentrations of plasma cytokines, antibodies, and acute phase proteins) during health and acute inflammatory conditions, including COVID-19. We discussed micronutrients (selenium, zinc, and vitamin D) with compelling evidence supporting immunomodulatory properties. Additionally, the synergistic effects of physical activity and dietary interventions on systemic immune markers are explored. Briefly, evidence suggests that dietary consumption of monounsaturated (oleic and palmitoleic acids) and omega-3 polyunsaturated fatty acids (eicosapentaenoic and docosahexaenoic acids) promotes anti-inflammatory properties. Food sources (fiber, prebiotics, probiotics, omega-3) and patterns (Mediterranean diet) increase the production of short-chain fatty acids, beneficially altering gut microbiota composition, which subsequently enhances the immunomodulatory properties of circulating immune cells. A positive synergistic role of nutrient supplementation (omega-3 and fiber) and physical activity on circulating C-reactive protein and interleukin-6 levels has been observed. Lastly, omega-3 supplementation during COVID-19 infection may reduce circulating C-reactive protein and pro-inflammatory cytokines and improves pain and fatigue symptoms. This review highlights recent findings that support the beneficial role of specific nutrients in promoting systemic immune function in healthy adults. However, to establish specific dietary recommendations to support optimal immune function, more research is required. Key takeaway: Increasing dietary fats (fish and olive oils) and specific micronutrients may positively impact systemic immune function in healthy adults. Evidence suggests that these nutrients promote immunomodulatory properties useful in resolving acute infection.
Keywords: MUFA; PUFA; immunity; infection; inflammation; nutrition; physical activity; selenium; vitamin D; zinc.