Current clinical practice emphasizes increasing calorie and protein intake to abate the nutritional decline that frequently occurs in cancer patients. Using an animal model of tumor-induced anorexia, we found that increasing the protein density of food resulted in a net increase in protein intake, but a decrease in the food intake of both healthy and tumor-bearing animals. The increased protein intake did not affect the nutritional status of tumor-bearing animals as indicated by body weight or serum levels of total protein, insulin, or insulin-like growth factor 1. These data suggest that factors regulating feeding responses to increased protein density of food are intact in hypophagic tumor-bearing rats, and that increased protein intake does not influence plasma levels of hormones requisite for protein synthesis. These data may partially explain why interventions to improve the nutritional intake of cancer patients have marginal effects on body weight, accrual of lean body mass, or synthesis of visceral proteins.