The type and amount of dietary fat, and in particular n-3 PUFA, may influence insulin action. The aim of this study was to examine the effects on HOMA indices from increased n-3 PUFA intakes at 3 and 6 months in a registered 12 month weight loss trial [ACTRN12608000425392]. The blinded RCT with 30 males and 88 females (aged 45+9.95yr; BMI 31.34+3.49kgm–2) compared a control diet (2MJ deficit, 30%fat + placebo) with two intervention groups (2MJ deficit, 30% fat emphasizing fish with placebo or supplement of 420mg EPA+ 210mg DHA). Differences between groups were assessed using repeated measures analysis of variance, where data was available at 0,3,6mo (n=73). A significant time effect was found for decreased HOMA-R (inverse of %S) (P=0.001), with post hoc analysis showing a significant difference between 0–3mo (P=0.006) and 0–6mo (P=0.002). Values for the control group were higher than for the intervention groups but the effect was not significant at 3–6mo (P=1.000). No effect was seen for HOMA(%β) (N=72). Energy restriction appears to decrease insulin resistance in overweight adults in the first 3 mo, and there may be added benefits with food or supplemental n-3 PUFA dietary enrichment.