Hollywood Gossip site Showbiz Spy is reporting that Megan Fox quit Transformers 3 because Michael Bay told her she looked "unhealthy" and ordered her to gain weight.
“Megan stormed out after a huge row with Michael Bay,” a source told British newspaper The Sun.“He thinks she has lost too much weight and looks too frail. He wanted her to put on some weight and it all kicked off. The crew don’t think she looks well, let alone the wholesome, curvy star they cast in the first film. She’s going for this gaunt, pale image and it just looks unhealthy."If this story sounds familiar, Megan Fox admitted that she was required by Michael Bay to gain weight for Transformers: Revenge of the Fallen saying at the time, “I should have toned up for 'Transformers' but I’m really lazy. I had to put on weight. I’d lost a lot of weight and got really scrawny, but I was told I had to put on size for 'Transformers' because Michael [Bay, the director] doesn’t like skinny girls."
No telling if this is true or false. I am leaning to false as just doesn't seem big enough reason. However, we do know she was on set (example image above) at least for a day or two and suddenly she was off the film so despite speculation the cause was not comments from last year (which probably didn't help) but something that occurred in just the last week.