The neonatal administration of monosodium glutamate (MSG) to rodents leads to obesity in the adult animal, characterized by increased fat storages. Chronic food restriction is known to induce reduction in body energy expenditure, as an adaptive mechanism to save energy. Our purpose was to examine whether obesity can alter the mechanism of energy conservation in food-restricted animals. Newborn female Wistar rats were injected either MSG (obese) or saline (control). At the age of 90 days, the animals were fed daily ad libitum (control and MSG) or restricted (50%) (control-restricted and MSG-restricted). After 30 days the animals were sacrificed and the energy balance was determined by calorimetric analysis. Some parameters of energy balance and body composition were affected by MSG treatment as well as food restriction. The percent reduction of the energy expenditure and fat content in MSG-restricted animals was lower than control-restricted animals, when compared with their respective ad libitum groups. These results indicate that all food-restricted animals were able to develop the mechanism of energy conservation, regardless of the obesity, but it was less efficient in MSG-obese animals.