Introduction: There is a large body of evidence about immunonutrition formulas; however, there are still doubts about their usefulness in routine clinical practice as compared with standard formulas. In the age of personalized medicine, new studies appear every year regarding several types of patients; therefore, an updated point of view on these formulas is necessary. Methods: The Embase database was searched from 2016 to 14 March 2022. Our criteria were articles published in English and Spanish. The evidence quality was evaluated using GRADEpro, and the review was developed according to the PRISMA statement. Results: In this review, a total of 65 unique records were retrieved; however, 36 articles did not meet the inclusion criteria and were thus excluded. In total, 29 articles were included in the final analysis. In the last few years, many meta-analyses have attempted to identify additional existing studies of surgical patients with certain pathologies, mainly oncological patients. Immunonutrition prior to oncological surgery was shown to cause a decrease in inflammatory markers in most of the studies, and the main clinical events that changed were the infectious complications after surgery. The length of stay and mortality data are controversial due to the specific risk factors associated with these events. Conclusions: The use of immunonutrition in patients who have undergone oncological surgery decreases the levels of inflammatory markers and infectious postoperative complications in almost all localizations. However, more studies are needed to assess the use of immunonutrition based on Enhanced Recovery After Surgery (ERAS) protocols.