The incretin hormones, GIP and GLP-1, enhance postprandial insulin secretion, promote adipogenesis, and regulate gastrointestinal motility and food intake. To date, a consensus on how the incretin response is altered in obesity is lacking. We investigated the effects of chronic high-fat-feeding on incretin secretion in the lymph fistula rat model. Male Sprague-Dawley rats (8 wk) were provided a semi-purified AIN93M high-fat (HF) or low-fat (LF) diet ad libitum for 3 or 13 wk; a high-fat pair-fed (HF-PF) group was included as a control during the 3 wk feeding trial. Energy intake, body weight, and body composition were regularly monitored. At the culmination of the feeding period, an intestinal lymphatic duct cannula and duodenal infusion tube were installed. All animals were challenged with a 3 ml Ensure bolus (3.125 kcal/animal) to measure lymphatic incretin secretion. Despite a significantly higher energy intake, both the 3 wk and 13 wk HF-fed animals did not have an increase in body weight and only a slight increase in body fat compared to LF-fed rats. Following the duodenal Ensure challenge, the 3 wk and 13 wk HF-fed rats had significantly greater lymphatic GIP and GLP-1 secretion than the LF-fed animals. Additionally, the HF-PF group displayed a secretion profile similar to the HF-fed animals for GIP but a similar pattern to the LF-fed animals for GLP-1. The HF-PF data suggest that the increased GIP secretion is driven by the greater percentage of fat intake, whereas the increased GLP-1 secretion is driven by the excess caloric intake.