McDonald’s burgers and fries don’t decompose.
This is due to several preservatives that are contained within their food. Several customers have documented leaving the food out for several months, and there were NO rotten smells or any other signs of decay - no insects even bothered to eat the food! Mold wouldn’t grow on it either.
But since the microbes can’t decompose the food, then your body shouldn’t be able to properly metabolize it either.
(Sources: 1, 2)