Obesity is the most prevalent nutritional disorder encountered in small animal medicine. Problems related with obesity are the higher incidence of morbidity and mortality. Nutritional and physical activity interventions have been common strategies employed; however, they have shown low compliance rates. Because of it more attention has been given to the nutrient composition of diets. Using the canine model, three experiments were conducted to examine the effect of fish oil or barley on protein and lipid metabolism, as well as postprandial glycemia, and nutrient digestibility in mature and in young adult dogs. In Exp. 1, seven female dogs were randomly assigned to one of two isonitrogenous and isocaloric diets, control (CO) or fish oil (FO), in a crossover design. Animals fed the FO diet tended to be more sensitive to glucose, showing a lower glucose half life. Cholesterol and HDL decreased (p<0.05) on the FO treatment. Overall, the supplementation of fish oil may improve glucose clearance rate and is effective in decreasing cholesterol in mature overweight dogs. In Exp. 2, eight female Beagles were randomly assigned to one of two isonitrogenous and isocaloric diets, control (CO) or fish oil (FO), in a crossover design. Overall, feeding a FO containing diet showed a protective effect against the rise of plasma CHOL and it increased plasma ghrelin levels. However, it did not appear to improve protein metabolism or postprandial glycemia in adult lean dogs. In Exp. 3, sixteen female dogs were randomly assigned to four experimental diets; control (40% corn) or three levels of barley (10, 20, 40%). The data suggest that inclusion of barley up to 40% in diets for adult dogs is well tolerated and does not negatively impact nutrient digestibility of the diets. However, inclusion of barley did not improve aspects related to fecal odor, postprandial glycemia, or plasma cholesterol. Overall, the research presented herein suggests that different nutritional strategies - dietary lipid or carbohydrate manipulation - may be beneficial in ameliorating health issues (e.g., hyperlipidemia) or in improving the health status of dogs (e.g., gut health by increased SCFA production).