What a tough question. On the one hand, if she's overweight, then she is likely to have some insight into both the reasons that people might be overweight and the difficulties encountered in losing. Messages about losing weight from the naturally thin, or quitting smoking from those who have never smoked, or abstinence, from those who have never had a tipple, are not very credible or useful.

And does someone need to be able to practice what they preach to be credible? I tell kids not to smoke at every opportunity - because I smoke and can't quit. I think I'm a pretty credible source about not smoking, precisely because of my experiences with trying to quit.

On the other hand, an addict who successfully quit could also give good guidance.

By the by, I have little respect for the unsupported argument that people overeat because of an "overstimulatory environment and uncontrolled food production."