Adipose 3 was a planet where the young Adipose were seeded and birthed before being taken home by the wet nurse that took care of them. At some point the Adipose First Family lost their nursing planet. At this point, they selected Earth as a new breeding planet, even though this was in violation of Galactic Law, because of the scale on which obesity was spread in Humans.
By 2009, Matron Cofelia of the Five-Straighten Classabindi Nursery Fleet, resided on Earth and had 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 discovered the operation, and fearing he might have alerted the Shadow Proclamation, Matron Cofelia advanced the birth plan, going to premature labour. She attempted to harvest as much Adipose as possible (killing the hosts) and then flee the Earth. However, this too was foiled by the Doctor and Donna Noble, 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 home, care of the Shadow Proclamation. (DW: Partners in Crime)
The true reason for Adipose 3's disappearance was due to Davros and the Daleks. They stole this planet, along with 26 others and put them in the Medusa Cascade. (DW: The Stolen Earth)