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AIM: The etiology of acute appendicitis (AA) is currently unclear. Low-fiber western dietary patterns (WDP) have long been thought to increase risk of AA, yet the strength and consistency of the evidence has not been quantified. METHOD: A systematic review was conducted following PRISMA guidelines (PROSPERO CRD420251024372). All human studies published in CENTRAL, MEDLINE, Embase, and Scopus from inception to December 2024 were retrieved. The primary outcome was the association between dietary exposure and risk of AA (case-control/cohort studies), and population incidence versus dietary intake at group level (ecological studies). Risk of bias was assessed using the ROBINS-E tool. Studies with insufficient standardized data for meta-analysis or regression were synthesized narratively. RESULTS: Twenty-one studies met the inclusion criteria. Most studies were deemed to have high risk of bias. A meta-analysis of four case-control studies showed lower fiber intake in AA patients (MD -4.53 g [95% CI -10.98; 1.94) p = 0.11; I2 = 98.3%). A meta-regression of ecological studies (15 subgroups, 3 variance-weighted studies) suggested a trend toward lower population incidence with higher fiber intake. A narrative synthesis of the remaining studies consistently linked low-fiber, high-meat, or sugar-dense WDPs with higher AA risk. CONCLUSION: The available evidence, although largely observational, suggests an inverse association between dietary fiber and AA, whereas meat- and sugar-rich WDPs appear to increase AA risk. This review highlights the large degree of uncertainty, heterogeneity, and low-quality data currently available.