Background <p>Early enteral nutrition (EN) is widely recommended for critically ill patients; however, its effects on clinical outcomes remain controversial. Previous systematic reviews have primarily focused on the timing of EN initiation, while the potential impact of nutritional adequacy during early feeding has been insufficiently evaluated. In addition, substantial variability exists in the definitions of “early” and “adequate” feeding across studies, contributing to inconsistent conclusions. Therefore, this systematic review and meta-analysis aimed to comprehensively evaluate the effects of EN initiation timing and nutritional adequacy on the prognosis of critically ill adults.</p> Method <p>An electronic search was conducted through the following databases: PubMed, EMBASE, the Cochrane Library, and Web of Science, on 5 May 2026. The search keywords included "Intensive Care Units", "Critical Illness", "Enteral Nutrition", and "Adult". The primary outcomes examined were 30-day mortality and the rate of infectious complications. To evaluate the risk of bias in the included studies, we used the Risk of Bias in Nonrandomized Studies of Interventions (ROBINS-I) and the Cochrane Risk of Bias 2 tool (RoB2). Statistical analyses were conducted via Stata version 14, employing odds ratios (ORs), weighted mean differences (WMDs), and 95% confidence intervals (CIs) for data synthesis. Publication bias was assessed via a funnel plot, Egger's test, Begg's test, and the trim-and-fill method. The certainty of evidence for each outcome was rated via the GRADE framework.</p> Results <p>A total of 19 studies comparing early enteral nutrition (early EN) versus delayed enteral nutrition (delayed EN) were included in the meta-analysis, and 4 studies comparing adequate early enteral nutrition (AEEN) versus inadequate early enteral nutrition (in-AEEN) were included in the qualitative review. Early EN significantly reduced the incidence of infectious complications in critically ill patients (OR = 0.33, 95% CI 0.16–0.69, <i>P</i> = 0.003). In addition, early EN was associated with shorter hospital stay (WMD = −4.20&#xa0;days, 95% CI −6.64 to −1.75, <i>P</i> &lt; 0.001) and ICU stay (WMD = −3.08&#xa0;days, 95% CI −4.31 to −1.85, <i>P</i> &lt; 0.001), although substantial heterogeneity was observed. No significant differences were identified in 30-day mortality (OR = 1.01, 95% CI 0.90–1.14, <i>P</i> = 0.403), duration of mechanical ventilation, or incidence of other complications between the two groups. Qualitative evidence from limited studies suggested that achieving adequate nutritional targets during early EN may further improve clinical outcomes and reduce mortality risk in critically ill patients. Taken together, these findings indicate that achieving the feeding energy target may increase the clinical benefits of early feeding, reduce mortality rates, and promote recovery. However, this assumption requires further comprehensive verification.</p> Conclusion <p>Early EN may reduce infectious complications and shorten hospital and ICU stay in critically ill patients, whereas its effects on mortality remain uncertain. Limited evidence suggests that achieving adequate nutritional targets during early EN may further improve clinical outcomes. Further high-quality studies are needed to determine optimal nutritional strategies in critically ill patients.</p> <p><i>Trial registration</i>: This systematic review and meta-analysis was prospectively registered in PROSPERO (CRD420251118159).</p>