1. A method for at least one of promoting weight loss by an animal, promoting weight loss by an animal while minimizing loss of lean body mass by the animal, minimizing a reduction in energy metabolism by an animal, reducing the risk of regaining weight by an animal after weight loss, and ameliorating undesirable animal behaviors associated with reduced caloric intake, the method comprising: feeding the animal for a first period a first diet containing calories that meet the animal's maintenance energy requirements; and feeding the animal for a second period a second diet containing calories that do not meet the animal's maintenance energy requirements; wherein the first period and the second period are periods of different durations and wherein the first period and the second period are independently selected from the group consisting of two days, three days, four days, five days, six days, a week, two weeks, and three weeks.