Abstract: Six studies with a total of 1039 patients were eligible for inclusion. The two largest studies were rated as low risk of bias for all assessed items. Four studies were rated as unclear risk of bias for randomization and allocation concealment. Two studies were rated as high risk of bias for incomplete outcome data and selective reporting. There was a marginal significant benefit of n-3 therapy for maintenance of remission. Thirty-nine per cent of patients in the n-3 group relapsed at 12 months compared to 47% of placebo patients (6 studies, 1039 patients; RR 0.77, 95% CI 0.61 to 0.98). A GRADE analysis rated the overall quality of the evidence for the primary outcome (i.e. relapse) as very low due to unexplained heterogeneity (I2 = 58%), publication bias, and a high or unknown risk of bias in four studies in the pooled analysis. When two large studies at low risk of bias were considered the benefit was no longer statistically significant. Thirty-seven per cent of patients in the n-3 group relapsed at 12 months compared to 42% of placebo patients (2 studies, 738 patients; RR 0.88, 95% CI 0.74 to 1.05). No significant heterogeneity was identified for this pooled analysis ( I2 = 0%). A GRADE analysis indicated that the overall quality of the evidence supporting this outcome was moderate due to sparse data (294 events). No serious adverse events were recorded in any of the studies but in a pooled analyses there was a significantly higher rate of diarrhea (4 studies, 862 patients; RR 1.36 95% CI 1.01 to 1.84) and upper gastrointestinal tract symptoms (5 studies, 999 patients; RR 1.65, 95% CI 1.25 to 2.18) in the n-3 treatment group. Evidence from two large high quality studies suggests that omega 3 fatty acids are probably ineffective for maintenance of remission in CD. Omega 3 fatty acids appear to be safe although they may cause diarrhea and upper gastrointestinal tract symptoms.

Plain-language summary: Randomized placebo-controlled studies that evaluated the effect of daily intake of capsules containing omega-3 fatty acids to maintain remission in Crohn's disease were reviewed. Six studies including 1039 patients were included in the review. A pooled analysis of six studies suggests a marginal benefit for omega 3 fatty acids over placebo (i.e. fake medicine) in preventing relapse of disease at one year. However, these results need to be interpreted with caution due to differences across the studies in terms of induction of remission regimens (e.g. surgical remission versus drug therapy) patients (e.g. adult versus pediatric patients) and medication regimens (e.g. some studies used different placebos), the possibility of publication bias (i.e. only studies with positive results are published) and low methodological quality in four studies in the pooled analysis. When the two largest and highest quality studies were pooled the results showed no benefit to omega-3 treatment over placebo. There were no serious side effects in any of the studies. Common side effects included unpleasant taste, bad breath, heartburn, nausea and diarrhea. Evidence from two large high quality studies suggests that omega 3 fatty acids are probably ineffective for maintenance of remission in CD. Omega 3 fatty acids appear to be safe although they may cause diarrhea and upper gastrointestinal tract symptoms.