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Baseline characteristics and quality of included RCTs

From 240 identified studies, 223 were excluded on initial screening. After full-text evaluation of the remaining 17 papers, eleven were included (Figure 1). Three papers reported data from the same trial,8–10 and one paper reported a trial with three arms, which was regarded as two separate studies,11 and thus the combined study contained ten RCTs with a total of 694 CRC patients (348 cases in the omega-3 group and 346 cases in the control group). Detailed baseline characteristics are listed in Table 1. Case numbers ranged from 18 to 148, and average age ranged from 50 to 71 years. Daily administered omega-3 PUFA ranged from 1 to 4 g in a fixed manner, or 0.05 to 0.2 g/kg adjusted to body weight. Preoperative nutrition support was used in three trials, postoperative nutrition support in four trials, and perioperative nutrition support in three trials. Omega-3 PUFA-enriched nutrition was administered orally in five trials: oral + jejunal infusion in one trial and parenteral in four trials.

(To view a larger version of Table 1, click here.)

Overall quality of the RCTs was moderate to high. As shown in Figure 2, four trials had unclear risk in selection bias, and three trials had unclear risk because of a lack of detailed information on random-sequence generation and concealment allocation.11,12,15–17 Only one trial showed a high risk of performance and detection bias, as the trial was not blinded.13

Effect of omega-3 PUFAs on postoperative infectious complications

Data for postoperative infectious complications were reported in eight trials. Meta-analyses in a fixed-effect model showed that the incidence of postoperative infectious complications was significantly lower in favor of omega-3 PUFAs compared with control (15.58% vs 24.76%, RR 0.63, 95% CI 0.47–0.86; P=0.004). There was a significant reduction in infectious complications in the pre- and postoperative subgroup (7.65% vs 18.23%, RR 0.43, 95% CI 0.24–0.76; P=0.004), though not in the perioperative subgroup (26.09% vs 33.33%, RR 0.78, 95% CI 0.54–1.13; P=0.19), as shown in Figure 3.

Effect of omega-3 PUFAs on postoperative SSI

The incidence of SSI was reported in eight trials. Meta-analysis results in a random-effect model revealed no significant difference between omega-3 PUFAs and control (7.17% vs 10.03%, RR 0.72, 95% CI 0.44–1.2; P=0.21). Subgroup analyses likewise showed no significant difference in pre- or postoperative (4.37% vs 7.73%, RR 0.58, 95% CI 0.25–1.34; P=0.2) or perioperative (10.87% vs 13.04%, RR 0.83, 95% CI 0.44–1.58; P=0.58) omega-3 PUFA-nutrition support, as shown in Figure 4.

Effect of omega-3 PUFAs on postoperative total complications

The incidence of postoperative total complications was reported in eight trials. The results revealed no significant difference in either overall meta-analyses (36.76% vs 47.02%, RR 0.67, 95% CI 0.43–1.04; P=0.08) or subgroup analyses of pre- or postoperative (36.61% vs 49.17%, RR 0.53, 95% CI 0.19–1.42; P=0.2) and perioperative (36.96% vs 44.20%, RR 0.82, 95% CI 0.53–1.25), P=0.35) omega-3 PUFA administration, as shown in Figure 5.

Effect of omega-3 PUFAs on postoperative inflammatory cytokines and CD4+:CD8+ cell ratio

Inflammatory cytokines were reported in four trials. Meta-analysis results in a fixed-effect model showed that omega-3 PUFA nutrition was associated with a lower level of TNFα (SMD −0.37, 95% CI −0.66 to −0.07; P=0.01) and IL-6 (SMD −0.36, 95% CI −0.66 to −0.07; P=0.02) compared with control, with no significant influence on CD4+:CD8+ cell ratio (SMD 0.36, 95% CI −0.04 to 0.76; P=0.08); as shown in Figure 6.

Effect of omega-3 PUFAs on postoperative hospital stay

Hospital stay was reported in six trials, and meta-analyses in a random-effect model showed a significantly reduced postoperative hospital stay in the omega-3 group compared with the control group (MD −2.09, 95% CI −3.71 to −0.48; P=0.01), as shown in Figure 7.