BACKGROUND: Dietary fatty acids are membrane components and lipid mediator precursors in the ovarian microenvironment. It is currently unclear how their composition determines the reproductive outcome in obesity-related infertility. AIMS: To map how saturated, monounsaturated and polyunsaturated fatty acids and their proportions affect oocyte competence, steroidogenesis and early embryonic development under obesity and high-fat diets. METHODS: The system retrieved English-language literature published from January 1, 2017 to September 30, 2026 in PubMed, Web of Science, Cochrane Library and Scopus. Predefined keywords for fatty acid types, reproductive outcomes and metabolic background were used, supplemented by manual searches. Two reviewers independently screened the titles, abstracts and full texts according to the pre-defined inclusion and exclusion criteria; eligible evidence included observational studies in humans, animal experiments and in vitro mechanism studies. Results were presented in a narrative summary; due to significant heterogeneity, no meta-analysis was conducted. RESULTS: A total of 699 retrieval records were identified, among which 82 studies met the inclusion criteria and were included in the data extraction. The analysis of these studies showed that the effect direction depended on the type of fatty acid and the context, rather than any single fatty acid: palmitic acid and stearic acid caused damage to oocyte maturation and blastocyst formation through endoplasmic reticulum stress (IRE1-XBP1) and mitochondrial stress (ceramide-AMPK/SIRT3). Oleic acid buffered lipid toxicity through lipid droplets, but excessive amounts inhibited CYP19A1 steroid synthesis and activated NLRP3/IL-1β. Omega-3 competed with arachidonic acid at COX-2 and exerted effects through NF-κB, Nrf2/GPX4 and GPR120, while omega-6-derived prostaglandins supported ovulation and implantation. CONCLUSION: Reducing palmitic acid, moderating oleic acid, increasing EPA and DHA and limiting omega-6 excess opens a non-pharmacological route, informing preconception nutrition in obesity and PCOS, refining assisted reproduction, and guiding ratio-based trials.