I speculate that this fatty is talking about that scenario in which the person tries to lose weight, and succeeds for a while, but then puts even more weight back on eventually through some magically unavoidable process whose nature is never quite clear (I assume that some supernatural willpower-trumping force such as karma or divine intervention is supposed to be involved; but it seems to be like Scientology's Xenu, in that you aren't supposed to talk explicitly about it with outsiders or even with low-level initiates). They do generally seem to accept that weight loss is possible, in the short term.  You'd have to be even more mentally damaged than the average fatto to fail to recognize that.