6.2. Omega-3 Fatty Acids Status
Plasma and serum fatty acid values can vary significantly based on an individual’s most recent meal, so they do not reflect long-term dietary intake. However, omega-3 status can be valued by calculating the percentage of the total serum phospholipid fatty acids. Although a normal range is not established, mean values for serum phospholipid EPA plus DHA are about 3–4% [206]. Omega-3 status could also be assessed analysing erythrocyte fatty acids. Harris and von Schacky proposed the “omega-3 index”, which represents the content of EPA plus DHA in red blood cells membranes, expressed as a percentage of total erythrocyte fatty acids, and reflects better long-term intake of EPA and DHA [207,208]. EPA and DHA are about 3–5% of erythrocyte fatty acids in Western populations with low fish intakes [209]. Moreover, the recent discovery of novel dietary omega-3 and omega-6 lipid-derived metabolites-such as resolvin, protectin, maresin, 17,18-epoxy-eicosatetraenoic acid, and microbe-dependent 10-hydroxy-cis-12-octadecenoic acid, and their potent biologic effects on the regulation of inflammation, have initiated a new era of nutritional immunology [210]. It has been shown that a synergy between omega-3 fatty acids and gut microbiota enhances the efficacy of immune checkpoint inhibitors [211].