High-fat diet using soybean meal as protein source: use for selecting rats prone and resistant to obesity

Objective The objective was to develop a high-fat, low cost diet, using soybean meal as protein source. This diet should effectively discriminate between rats prone and resistant to obesity and allow the obese phenotype to be achieved in the animals that are prone to obesity. Furthermore, the diet must be palatable and not be rejected by the animal in the short run. Methods The chow was obtained by mixing the following ingredients: condensed milk (15.5%), peanuts (18.5%), soybean meal (20.0%), corn oil (6.0%), Bio Tec chow (30.0%) and chocolate wafer cookies (10.0%). In order to make it appropriate for rats, the mixture was pelleted and subjected to food analysis. The chow was offered to Wistar rats for a week. The animals were subsequently separated according to weight gained. The upper third group was considered prone to obesity and the lower third group was considered resistant to obesity. The animals were sacrificed 80 days later to determine body weight, food intake, retroperitoneal, periepididymal and carcass fats and total fats. Results Food analysis found that the chow had an energy density of 5.31 Kcal/g, 22.3% fat, 22.2% protein, 15.9% fiber and 35.7% carbohydrates. After being fed for 87 days with the high-fat diet, obesity-prone rats had higher body weight and retroperitoneal, periepididymal and total fats than obesity-resistant animals (p < 0.05). Food intake was also higher among obesity-prone rats (p < 0.05). The replacement of casein by soybean meal as protein source reduced the cost of the study by 96.0%. Conclusion The substitution of casein by soybean meal in a high-fat diet allows cost reduction and the identification of obese-prone rats. Continuous use of this high-fat diet resulted in the development of the obese phenotype, as seen with other diets used in the literature.