Taking on a full marathon for the first time is not an easy decision to make. There is always a fight between the body and the mind. Which in many cases, is the body fighting the mind. Probably because the mind is always harsh on decisions towards the body, and the poor body must just endure. When the mind is convinced, the body cant do anything but to obey.
It will be equally fair that when the mind has decided on the distance, it must also make a bold decision to train and shape the body to be ready for that distance. Doing a 42.2km is nothing other than making a decision, and commit to a training programme. Proper diet is also just relative. The answer to the question of, if it will be easy or difficult simply depend to ones training dedication.