THE EFFECT OF FASTING AND REFEEDING ON OXYGEN-CONSUMPTION BY RATS

Oxygen consumption is usually measured on fasted animals to avoid the thermal effect of feeding. However, fasting itself may decrease oxygen consumption as a way of conserving energy. The present study was unde rtaken to determine how long the fasting period should be to avoid the thermal effect of feeding without promoting a further decrease in oxy gen consumption by the activation of energy-conservation mechanisms. O xygen consumption was also measured to evaluate the effect of refeedin g after different fasting periods. There was a 16% decrease in oxygen consumption from 0 to 12 h fasting related to the thermal effect of fe eding, followed by a less intense (12%) decrease from 12 to 48 h fasti ng resulting from the energy conservation mechanism. During refeeding, oxygen consumption was higher during the first 30-min period than dur ing the last 30-min period of the 1-h measurement, indicating the prob able presence of a cephalic phase of postprandial thermogenesis. We co nclude that 12-h fasting is the most appropriate period to avoid the t hermal effect of feeding without significantly stimulating the energy conservation mechanism.