Obesity is a growing concern for the nation. Increased interest has focused on the gastrointestinal tract (GI) properties that may impact nutrient absorption. To compare potential differences in GI morphology, we examined the histological characteristics of the digestive tracts of lean and obese rats. High-capacity runners (HCR) are lean, whereas low-capacity runners (LCR) are obese, yet HCR eat more than LCR. Intestines were collected from 12 HCR and 12 LCR adult male rats. After fixation with 10% formalin, a sample from the jejunum was paraffin embedded and sectioned cross-sectionally on a microtome, followed by hematoxylin and eosin (H&E) staining. Using microscopy, we were able to quantify aspects of jejunum such as villi length, diameter, and surface area, and number of crypts per unit area. Preliminary findings showed thinner mucosal layers in the LCR than in the HCR. Longer villi were seen in the HCR than LCR jejunum; however, the number of villi was greater in the LCR. Ongoing analyses will calculate the surface area of villi. The total number of villi and surface area could differentially impact nutrient absorption.