A memoir is only interesting, by it's very nature, to the people whom it effects, and so yes of course it would an interesting subject, as your target audience are in direct comparison to it's subject.
I think if sympathetically done, with an honest and expressed view of the experiences and feelings everyone has throughout the process, would actually be a breathe of fresh air.
The problem is, as with all these type of books so far, is that an ex anything can be extremely condescending, and frankly patronising - a sort of "I did it, why can't you?" attitude - which of course isn't helpful.
But if you can hold that back, and be absolutely honest about every aspect of your experience, then yes fantastic - if you felt depressed from it, say so; if you cried, say so; if you now feel elated at your weight loss, say so etc.
I think something raw, would be a massive hit.