Obesity-induced insulin resistance (IR) is a common problem in humans as well as domestic dogs. It is well-known that this syndrome is associated with many modifications but it is still unclear if the changes are alterations or adaptations. The purpose of this study was to develop obesity-induced IR in dogs, through a long-term overfeeding period, and to explore hormonal and metabolic disturbances associated with the development of this syndrome. Dogs were overfed for 7 months. Body weight increased by 43 ± 5%, and insulin sensitivity decreased by 44 ± 5%. Plasma insulin-like growth factor 1 (IGF1), tumour necrosis factor alpha (TNFα), and non-esterified fatty acids (NEFA) concentrations progressively increased during the overfeeding period (IGF1: 111 ± 13 to 266 ± 32 ng/ml, p < 0.001; TNFα: 5 ± 5 to 134 ± 41 pg/ml; NEFA: 0.974 ± 0.094 to 1.590 ± 0.127 mmol/l, p < 0.05). These metabolic and hormonal impairments are associated with IR, in obese dogs, and could explain, at least in part, the outbreak of this syndrome.