Calorie restriction (CR) without malnutrition is a dietary intervention known to improve metabolic health in humans. To investigate the mechanisms involved in this, rodent models are often used which involve giving them a portion of food at one time point during the day. This asks the question is it the longer fasting period or the calorie restriction itself, causing the improvements. Thus, we undertook a study to investigate this phenomenon. At 12 weeks of age, C57BL6 mice (9 male and 9 female per group) were randomly assigned to either the control diet (ad lib; 21% protein, 64% carbohydrate, 15% fat; 14.7 kj/g energy density), 20% calorie restriction of the control diet (given at 4pm daily) or the cellulose diluted diet (ad lib; same percentage as control diet but at 10.5 kj/g energy density) for 6 months. Body weight and food intake were measured throughout the experiment while body composition and oGTT were measured just prior to cull. Results showed that the calorie restricted groups ate a similar amount of kilojoules per day, being ~20% lower than controls (Control 48kj/day, 20%CR 37kj/day, 37 kj/day). This resulted in body weight, body length and fat mass (Control 10.6±0.9g; 20%CR 5.0±0.8g; CRdil 4.5±0.6g; p<0.001) being reduced to a similar amount in the restricted groups compared to controls, while lean mass was similar in all 3 groups. Glucose tolerance tests were similarly decreased in the restricted groups (control AUC, 1216±40; 20%CR, 985±44; CRdil, 1023±39 mM/90min; p<0.001). These results suggest that calorie restriction, not fasting time, is a likely mediator of improved metabolic health. Further investigations will determine if the reductions seen in both groups are via similar molecular mechanisms and if they persist long-term.