The shakes are a possibility as long as the carbs are low. Problem with most bars is that they tend to have nuts/seeds, some bad fats and sugar to make them more palatable.
I'm trying to lose some weight and the theory behind the programme is plenty protein and veg, low carbs/fats, and the tricky bit, especially when I'm at work, is to eat at least every 2-3 hours. It all seems very logical and in a nutshell revolves around making the body use fat as an the energy source rather than storing it, and also naturally speeds up the metabolism. Bizarrely, you are not allowed to do any strenuous exercise in the 1st 4 weeks as this will have a detrimental effect on the muscle/fat storage/metabolisation equation, which unfortunately means my assault on the UK race scene will have to wait 😆