Obesity is the most prevalent nutritional disorder in cats (Felis catus; Hoenig et al., 2011). High carbohydrate diets, prescribed for weight loss, may contribute to adiposity (Thiess et al., 2004). The effects of a high fat (HF; 30% fat, 10% carbohydrate), high carbohydrate (HC; 10% fat, 46% carbohydrate) and a moderate diet (15% fat, 30% carbohydrate) supplemented with a calorie restriction mimetic (mannoheptulose (MH); 8 mg/kg BW), fed to energy requirements, on feline metabolism and behaviour were investigated (n=20; 4 ± 2.5 kg). An 11 week acclimation procedure was designed to adapt cats to 24-hr restriction within a chamber used for indirect calorimetry. Stress indicative behaviour (Kessler and Turner, 1997) declined with repreated exposure to increasing lengths of restriction within chambers and on week 11 stress levels were low and consistent (P<0.05). Neither the HF nor HC diet impacted body weight (p>0.05); however, HF feeding caused an increase in body fat (0.75 kg (baseline) vs. 1 kg (86d)) after long-term feeding. Energy expenditure (EE) was not impacted by dietary fat/carbohydrate. Respiratory quotients (RQ) increased and decreased with exposure to the HC (fasted= 0.80 ± 0.008; fed= 0.87 ± 0.008), HF (fasted= 0.76 ± 0.008; fed= 0.78 ± 0.008) diet, respectively. Glucose to insulin (G:I) ratio increased with HF feeding; indicating improved insulin sensitivity. Physical activity, measured using accelerometers, declined with HF (-1.6 counts/hr) and HC (-2.8 counts/hr) feeding from baseline. T-maze performance decreased and increased with HF (-0.85 score/10) and HC (0.85 score/10) feeding from baseline (p<0.05). MH did not impact body weight or composition (p>0.05). Area under the curve for EE increased during the 15-22 hour post feeding with MH treatment (2370.3 (-MH) vs. 3292.0 (+MH) ± 0.0002). RQ and G:I were not impacted by MH (p>0.05). MH increased play motivation, measured using obstruction tests (p<0.05). Diets high in carbohydrate are not ideal for weight loss since they negatively impact insulin sensitivity and voluntary EE. Diets promoting elevated EE, activity and normal glucose/insulin profiles are ideal for weight control and MH offers a unique opportunity for use in weight loss regimes. / This work was funded by Procter and Gamble Co.