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AIM: To investigate the relationships of serum fatty acid (FA) composition and estimated desaturase activities with the liver fat marker alanine aminotransferase (ALT). METHODS: 546 Swedish elderly men of a population-based cohort participated in this cross-sectional study. FA composition was assessed in serum cholesterol esters to determine dietary fat quality (e.g. linoleic) and desaturation products (e.g. dihomo-gamma-linolenic acid). Desaturase indices, including stearoyl coenzymeA desaturase-1 (SCD-1), were calculated by FA product-to-precursor ratios. RESULTS: In linear regression analyses adjusting for lifestyle, abdominal obesity and insulin sensitivity, the dietary biomarker linoleic acid (n-6), but not n-3 FAs, was inversely related to ALT. Desaturation products including palmitoleic, oleic, gamma-linolenic and dihomo-gamma-linolenic acids, and Delta6-desaturase and SCD-1 indices were directly related to ALT (all p<0.05). After further adjustment for factors previously linked to fatty liver (i.e. serum lipids, adiponectin concentrations), SCD-1 index (p=0.004) and insulin resistance (p<0.0001) were independent determinants of ALT activity, whereas waist circumference, triglycerides, non-esterified FA and adiponectin were not. CONCLUSION: A low dietary intake of linoleic acid and elevated SCD-1 index may contribute to higher ALT activity in elderly men, even independently of obesity and insulin resistance.