In the bonus material of I Am Legend there was the personal trainer of Will Smith talking about different looks, even from one day to the next.

The scenes and takes with a more cut look were shot one day, the ones with more or dialogue at all another day, as carbohydrates are needed for brain activity like remembering lines of a script and performing them. Or so he pointed out.

"Low carb / high fiber" might be the Atkins thing. I have no actual idea or extended interest and am guessing.

The whole "do this, look like that"-approach does not add up and appears to be one of the most obvious signs of blatant hobby science in various forms and flavours usually found in the supplement and book markets.