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Background: Omentin is an adipokine with anti-inflammatory and insulin-sensitizing effects that can play a protective role against cardiovascular disease and diabetes. The aim was to systematically review and summarize the existing evidence on the association between overall dietary intake and omentin gene expression and circulation. Summary: A literature search was conducted in PubMed, Scopus, and Web of Science up to September 2019. Of the 1,940 retrieved articles, 20 relevant studies were included, 6 of which were observational, 11 were clinical trials in humans, and 3 were animal studies. Four randomized controlled trials (RCTs) had a high risk of bias (RoB), 1 had “some concerns”, and 2 had a low RoB. Among the nonrandomized studies with comparators, 4 had a serious RoB and 2 had a moderate RoB. In the experimental animal studies with a moderate RoB, conflicting results for omentin serum concentration were found for high-fat and low-fat diets. A high-fat diet (HFD) was shown to reduce omentin gene expression in one animal study. In the observational studies, omentin serum concentration was reduced by Ramadan fasting and saturated fatty acid (SFA) intake, and an increase in omentin gene expression was observed with monounsaturated fatty acid (MUFA) intake. There was no association of dietary inflammatory index (DII), macronutrient intake, or total calorie intake with omentin plasma concentrations. In the human interventional studies, omentin plasma concentration increased with a long-term low-calorie, low-fat diet (LFD), and no change was seen with a HFD or a short-term low-calorie diet (LCD). Key Messages: It seems that a long-term diet with a lower fat content and a balanced distribution of fatty acids, i.e., a higher MUFA and lower SFA intake, may effectively increase omentin plasma concentration, possibly via improved insulin resistance and reduced inflammation, but more research is needed to confirm or refute this.