AbstractThe effects of fat intake from different dietary sources on bladder cancer (BC) risk remains unidentified. Therefore, the present study aimed to investigate the association between fat intakes and BC risk by merging world data on this topic. Data from 11 cohort studies in the BLadder cancer Epidemiology and Nutritional Determinants (BLEND) study, provided sufficient information on fat intake for a total of 2731 BC cases and 544 452 noncases, which yielded 5 400 168 person‐years of follow‐up. Hazard ratios (HRs), with corresponding 95% confidence intervals (CIs), were estimated using Cox‐regression models stratified on cohort. Analyses were adjusted for total energy intake in kilocalories, gender, smoking status (model‐1) and additionally for sugar and sugar products, beers, wine, dressing and plant‐based and fruits intakes (model‐2). Among women, an inverse association was observed between mono‐unsaturated fatty acids (MUFAs) and BC risk (HR comparing the highest with the lowest tertile: 0.73, 95% CI: 0.58‐0.93, P‐trend = .01). Overall, this preventative effect of MUFAs on BC risk was only observed for the nonmuscle invasive bladder cancer (NMIBC) subtype (HR: 0.69, 95% CI: 0.53‐0.91, P‐trend = .004). Among men, a higher intake of total cholesterol was associated with an increased BC risk (HR: 1.37, 95% CI: 1.16‐1.61, P‐trend = .01). No other significant associations were observed. This large prospective study adds new insights into the role of fat and oils in BC carcinogenesis, showing an inverse association between consumption of MUFAs and the development of BC among women and a direct association between higher intakes of dietary cholesterol and BC risk among men.