A high fat diet significantly increases epididymal fat, serum free fatty acids and reduces the number of GLP-1-positive cells in the distal intestine . Epididymal fat (A-B) and fasting serum free fatty acids (C) are significantly increased in animals receiving HFD (55% and 41% increase, respectively) and reduced by a 14-day 300 mg/day metformin treatment (22% and 59% reduction, respectively). (n = 8 for control diet group, n = 6 for HFD group, n = 4 for HFD group receiving metformin). There is a trend towards a reduced number of GLP-1-immunopositive cells in intestinal tissue sections from animals on HFD (D and G) as compared to animals receiving a control diet (E and G); 55% reduction, p = 0.134, an effect indicated to be reversed by daily administration of metformin for 14 consecutive days (F and G), (n = 3 for each treatment group). Scale bar: 25 μm. No significant effect can be determined of a HFD or metformin treatment on prandial serum GLP-1 (7–36 and 9–36) levels (H); HFD - 46% increase, p = 0.095 and HFD + metformin – 72% increase, p = 0.23. Intestinal expression of GLP-1R mRNA was significantly upregulated in response to a HFD (53% increase), while normalized by metformin treatment. (n = 8 for control diet group, n = 6 for HFD group, n = 4 for HFD group receiving metformin). GLP-1R mRNA expression was normalized with mRNA expression of GAPDH, which was used as an internal control. A.u.; Arbitrary units (I). Bars represent mean ± SEM. *, p < 0.05 compared with control group. #, p < 0.05 compared with HFD group. Statistical analysis was performed using one-way ANOVA.