Adipose 3, also known as Breeding Planet One, was the planet used by the Adipose First Family to breed their young, before being taken home by the wet nurse that took care of them.
At some point before 2009 the planet was stolen by the New Dalek Empire and transported to the Medusa Cascade.(DW: The Stolen Earth) Faced with the disappearance, the first family decided to select Earth as a new breeding planet, even though this was in violation of Galactic Law, because of the scale on which obesity was present in Humans.
By 2009, Matron Cofelia of the Five-Straighten Classabindi Nursery Fleet, resided on Earth and covertly seeded Humans through the front of a weight loss product distributed through Adipose Industries. At first, all went well and she managed to seed one million customers within the Greater London area, but at the advent of going nation-wide with the product, the Doctor and Donna Noble discovered the operation, and fearing that they might have alerted the Shadow Proclamation, Matron Cofelia advanced the birth plan, going to premature labour. She attempted to harvest as many Adipose as possible (killing the hosts) and then flee the Earth. However, this too was foiled by the doctor, and in the end only 10,000 young were birthed and marched openly through central London to reach their Nursery Ship. The first family proceeded to kill their accomplice and the young were taken into the care of the Shadow Proclamation. (DW: Partners in Crime)
In the Medusa Cascade, Adipose 3 and 26 other planets formed the engine of a Reality Bomb with which the New Dalek Empire planned to unmake every universe. It was returned by the Doctor to its proper place in space and time after the Daleks were thwarted. (DW: The Stolen Earth/Journey's End)