Don’t expect to be perfect immediately – or ever actually. It takes a lifetime to build your habits and it takes time to change them too. At first, changing your habits and behaviours can take effort and concentration but with time they become easy.
There are going to be times when you are tired or stressed or other times when your defences are low and you take the path of least resistance. At first, this path will be your old habits, such as not having breakfast and having to eat the pastries in the morning meeting because you are so hungry. But the more you practise your new way of eating, the more habitual it becomes and then that becomes your path of least resistance.