People are always going to make these arguments. Yes, I know that there's scientific evidence that your mass effects your weight and that hunger, metabolism, etc. effect your mass. But we have to look at effect sizes. Whatever diet you try, you are only every going to have, at most, a modest effect on your own mass which will indirectly lower your weight.

I challenge people to go out there and start launching chunks of matter on escape trajectories from Earth. Yes it is hard, yes it takes a lot of energy, but you will start reducing the force of gravitational attraction acting on you. These are real results, not just a temporary change.