Moderate exercise attenuates postprandial lipaemia and insulinaemia, and increases fat oxidation for at least 24 h post-exercise. The magnitude of this effect is related to exercise energy expenditure, but it is unclear whether these changes are the consequence of exercise per se or the associated energy deficit. This study aimed to 1) determine the effects of exercise, with and without energy deficit, on postprandial metabolism, and 2) determine whether exercise-induced changes in postprandial triglyceride (TG) responses were related to changes in whole-body and hepatic fat oxidation. Thirteen men (age 40±8 y, BMI 31.1±3.0 kg/m2) [mean±SD] completed three 2-day trials in random order. On Day 1: subjects rested (C), walked briskly to expend 27 kJ/kg body mass (E), or completed the same walk with all energy expended replaced (ER). On Day 2: subjects arrived after a 12 h fast and rested for 8.5 h. During this time breakfast and lunch were provided (each with 97 g carbohydrate, 33 g fat, 28 g protein, 3.3 MJ energy). Regular blood samples were collected for measurement of TG, insulin, and 3-hydroxybutyrate (3-OHB; a marker of hepatic fatty acid oxidation). Indirect calorimetry with a ventilated hood was used to determine whole-body substrate oxidation. For 3 d preceding Day 2, subjects avoided alcohol, planned exercise (other than test walks) and had all food provided by the experimenter. Time-averaged postprandial TG concentrations were C: 2.0±0.3 mmol/l, E: 1.7±0.3 mmol/l and ER: 1.9±0.2 mmol/l (p<0.02; ANOVA, for C vs E, E vs ER) [mean±SEM]. Postprandial insulin concentrations were C: 44.1±5.0 mU/l, E: 36.0±3.8 mU/l and ER: 39.6±4.5 mU/l (p<0.03 for C vs E, C vs ER, E vs ER). Postprandial 3-OHB concentrations were C: 20±2 µmol/l, E: 28±2 µmol/l and ER: 23±2 µmol/l (p<0.05 for C vs E, E vs ER). Postprandial fat oxidation over the 8.5 h was C: 37.0±2.0 g, E: 44.6±2.3 g and ER: 40.6±2.1 g (p<0.05 for C vs E, C vs ER, E vs ER). Significant correlations were observed between the exercise-induced changes in postprandial TG and postprandial 3-OHB concentrations (r=0.48, p=0.01; Pearson Correlation) and the exercise-induced changes in postprandial TG and postprandial fat oxidation (r=0.74, p<0.0005). In conclusion, prior moderate exercise without energy deficit attenuated postprandial insulinaemia and increased fat oxidation although an energy deficit augmented these effects. An energy deficit was needed to elicit an exercise-induced reduction in postprandial TG concentrations. Furthermore, exercise-induced changes in postprandial TG concentrations were related to changes in whole body and hepatic fat oxidation.