Energy balance of rats subjected to continuous and intermittent food restriction.

Data from our laboratory have demonstrated that food restriction leads to alterations in energy balance such as reduced energy expenditure as an energy conservation mechanism. Food restriction may be imposed on the animals in different ways. The most common is to give equal daily amounts of restricted food. Alternatively, food may be given once every two or three days so that the food intake is not constant with the animal tending to eat more on the first day and be very restricted during the subsequent days of the period. The former model may elicit habituation to the low food intake while the latter may decrease the habituation stimulus since the food intake is not constant. Energy balance was determined in 3 groups of female rats weighing 206.7 +/- 2.0 g (N = 6 each): control (C), which received food ad libitum; continuously food restricted (CR), which received 8 g of food daily, and intermittently food restricted (IR), which received 24 g of food every 3 days. On the 21st day of treatment, the animals from both food-restricted groups showed a similar reduction of body weight (-47.9 +/- 5.1 and -55.8 +/- 4.0 g for CR and IR, respectively) and body energy (-501.0 +/- 65.5 and -427.0 +/- 82.1 for CR and IR, respectively), and they had similar energy expenditure (2643 +/- 72 and 2518 +/- 97 for CR and IR, respectively) which was different from ad libitum controls (4.6 +/- 2.9 body weight gain, 277.3 +/- 42.5 body energy gain and 4574 +/- 290 energy expenditure). Body weight decreased continuously in the CR group while in the IR group it followed the pattern of food intake with up-and-down shifts. We conclude that the energy balance pattern presented by food-restricted animals is the same regardless of the form of food restriction imposed.