There isn’t one. A sensible mix based on the standard NHS advice is good idea, but as far as 5:2 is concerned, it is calorie based. Restrict your calories to 600 per day for a male or 500 for a female twice each week and do not exceed your Total Daily Energy Expenditure (TDEE) the rest of the week and you will lose weight. If you enter your details – height, weight, exercise levels – on the tracker (top right of the screen) it will tell you your TDEE. After that you need some idea of how many calories are in what you eat. It is very flexible – I have been known to take the view that there about as many calories in a whiskey as there are in a boiled egg. Not a good idea every day but it does not affect the end result.