You're referring to "Fat Farm" by Orson Scott Card which originally appeared in his collection of short stories entitled 'Maps in a Mirror'
Per the Wikipedia article;
Martin Barth is a very rich man with a serious overeating problem. When his obesity interferes with his enjoyment of his lifestyle, he goes to a secret clinic, gets himself cloned and then transfers his memories into the clone.
After Barth has legally transferred his identity to his replacement and it is too late to change his mind, he is told that he is now the property of the company that runs the clinic. His name is now "H", because he is the eighth "edition" of himself to go through the process. He has a choice: immediate death or "an assignment". Since he doesn't want to die he agrees to work for the company. He is then dragged into the middle of nowhere and forced to do manual labor so that he will be in shape for the unspecified job they want him to do.
After two years, with only a brutal overseer for the company, "H" is given his assignment. He leaves the camp, just in time to see his clone - "I" - who is now fat dragged into the camp to begin the process over again.
As his plane is taking off, "H" thinks about how much he hates himself for repeating this process over and over again. He wishes that the newest clone would suffer even more than he had. After telling this to the businessman, who is his new supervisor, the young man laughs out loud. He explains that the overseer (or "old man" as "H" refers to him) is actually "A", the original.