Adult dogs have a better supply of body fat as well as a liver that is fully capable of making glucose (energy) during periods of starvation. (preventivevet.com)
Healthy animals can combat long periods of starvation through decreased metabolic rate, but animals that are sick or injured require more energy, which increases metabolism. (canismajor.com)
So eating a high calorie meal (of course not junk food but well balanced one) after a prolonged period of starvation is the way to go. (fitnessandpower.com)