In a nutshell if you eat any type of carbohydrate (simple, complex, fibrous) on their own your pancreas will release insulin, causing an insulin spike. What goes up must come down, causing your body to "crave" more of the same to get the levels up again.
Mixing simple, complex & fibrous carbs with proteins/fats will keep your levels regular and allow your body to function smoother.
Another note is that your "pleasure" receptors of the brain know your habits & your mind has already been programmed by you to say yes to want that second slice of cake because you usually do or have those biscuits with your tea etc. That is why breaking the habits is hard - your body dosen't want chocolate like you think it just wants a quick energy boost.... by keeping your levels steady you will reduce cravings.
Being hungry isn't good for you, you won't burn more fat as your body goes into starvation mode. Fuel it properly to function efficiently.
Ensure you eat fresh food daily with proteins at each meal to keep you full & ensure you eat a serving daily healthy fats (avocado, olive oil, coconut oil, almonds etc)