I've had people mention it on job interviews since we do behavioral style interviews with questions such as "tell me about a time when you...." People have used that as an example of overcoming obstacles or persevering in a difficult situation. With that interviewing style I find that people often use both personal and professional examples. Those who have mentioned it have indicated they lost large amounts of weight (such as 100+ pounds).
Having said that, I would not personally mention it.
I personally wouldn't, the history of the size of my body does not need to be discussed unless the job was relevant (personal trainer, nutrition expert, blahblah).
