Glucose flux in relation to energy expenditure in malnourished patients with and without cancer during periods of fasting and feeding.

Glucose dynamics, energy metabolism, and nitrogen balance were studied in eight malnourished cancer patients and seven malnourished patients without cancer. Glucose flux was measured by single injection of [6-3H]glucose and [U-14C]glucose. Energy expenditure was measured by indirect calorimetry. Each patient was studied after an overnight fast and during constant gastric infusion of a formula diet. Cancer patients had elevated glucose flux when fasting, corresponding to 42% of their spontaneous daily intake of glucose. At least one-half of the elevated flux in cancer patients compared with controls was due to increased recycling of glucose carbon after an overnight fast. Feeding doubled the total glucose flux in both cancer and control patients. The recycling was unchanged in the cancer group and disappeared in the controls during feeding. The increased glucose flux in cancer patients was concomitant with normal resting energy expenditure during periods of both fasting and feeding. Glucose flux in relation to energy expenditure was doubled in cancer patients compared to controls, and the glucose flux in fed cancer patients was similar to the rate of glucose infusion, which shows that the endogenous production of glucose was not inhibited. Cancer and control patients reached a comparable positive energy and nitrogen balance, allowing for their overall caloric intake. Our results show that cancer patients seem to have a characteristically increased glucose demand, which contributes to their weight loss when fasting. The energy drain by this elevated glucose flux can explain, as a maximum estimate, a loss of about 0.9 kg of body fat per 30-day period.