The impact of feeding a hypercaloric parenteral solution on N balance, energy metabolism, and muscle strength has been investigated in cachectic patients with gastrointestinal cancer and in malnourished patients without evidence of cancer (controls). Patients were examined during 5% dextrose administration (D5W) for 2 days, followed by an infusion of a carbohydrate-based (53% carbohydrate, CB) or fat-based (55% fat, FB) diet with a constant protein intake. Diets were administered for 1 week each, in a randomized crossover design. During D5W, cancerous patients demonstrated a similar energy expenditure, but significantly lower N balance (p less than 0.005) than controls. Compared to control patients, N balance in cancerous patients was similar on the CB diet and significantly lower during the FB diet (p less than 0.025). Unlike the control patients, muscle strength and endurance tests did not improve after 2 weeks of feeding in cancerous patients. The cancerous patients differ from controls because they are hypercatabolic (especially during D5W administration), and they showed no improvement in muscle strength with 2 weeks of feeding.