Fatty acid supplementation increases muscle mass and function in older adults, but the effect of habitual dietary intake is uncertain. Therefore, the objective of this study was to examine the association between habitual dietary fat intake and risk of muscle weakness and lower-extremity functional impairment (LEFI) in older adults. Prospective study with 1873 individuals aged ≥60 years from the Seniors-ENRICA cohort. In 2008-10 and 2012, a validated face-to-face diet history was used to record the one-year consumption of up to 880 foods. Then, fatty acids, other nutrients and energy intake were estimated using standard food composition tables. Means of intake between these years were calculated to represent cumulative consumption over the follow-up. Study participants were followed up through 2015 to assess incident muscle weakness (lowest quintile of grip strength) and incident LEFI (Short Physical Performance Battery score ≤6). Analyses were performed with Cox regression and adjusted for the main confounders, including other types of fatty acids. Over a median follow-up of 5.2 years, 331 participants developed muscle weakness and 397 LEFI. Intake of saturated fatty acids (SFA) did not show an association with muscle weakness but was associated with higher risk of LEFI (multivariable hazard ratio (HR) for tertile 3 vs. tertile 1: 1.15; 95% confidence interval: 1.05-2.01; p-trend = 0.02). This association was mostly due to consumption of Spanish cold cuts and pastry and, to a lesser extent, dairy. Monounsaturated fatty acids (MUFA) intake was associated with lower risk of muscle weakness (HR t3 vs. t1: 0.73; 0.54-0.99; p trend = 0.04), and intake of n-3 polyunsaturated fatty acids (PUFA) was associated with reduced risk of both muscle weakness (0.70; 0.52-0.95; p-trend = 0.02) and LEFI (0.49; 0.35-0.68; p-trend <0.001). Olive oil and blue fish, the main sources of MUFA and PUFA, were also associated with lower risk of muscle weakness and LEFI. Habitual intake of SFA was associated with increased risk of LEFI. By contrast, habitual intake of MUFA and PUFA were associated with lower risk of physical performance impairment. Copyright © 2020 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.