My DH did mutter a bit about the whole fruit acid thing, saying that as the acid was netralised it would create hydrocarbons, and that there would be no practical difference between citric and malic acid in this respect. But I don't know, I didn't do organic chemistry at advanced level.
I'm never sure about being able to blame one thing for lack of weight loss, after all we know how low calorie this diet thing is, even if we were taking in an extra 100 calories a day it would still only make 1/5th lb difference at weigh in.