Even better than weight loss comparisons are before and after visual effects shots. Of course, weight loss might also just be VFX.
These have been culled from around the internet. Plenty to chose from. Great selections can be found here, here, and here, for starters.
I wanted to assemble a bunch in one spot.
I've always found movie magic fascinating. It's astonishing how little is real, and it must be a strain for some actors. A vivid imagination and a child like sense of play will be essential for actors in the future.
Think of Sky Captain and the World of Tomorrow. Angelina Jolie and Jude Law excelled when planted in CGI environments, but Paltrow struggled. She's great opposite real people, but against imaginary elements, she wasn't convincing. At least in that early go around. She's better in Iron Man.
Although the blue stuffed toy gives The Life of Pi an even more interesting psychological twist, as a descent into madness.
Most of the shots are of vast, outlandish vistas. Yet some are mundane, and you'd never guess they were effects shots. These days, it's more economical to do CGI than go on location. Partial sets filled out by CGI are the order of the day.