If your digestion isn't working properly you won't be able to digest and absorb the nutrients form your food, so you won't get the full benefits of improving your diet.
Digestion starts in the mouth where your food should be broken down into a puree so it's vital to make you sure chew all your food properly until there are no more solid lumps in it, before swallowing. This may feel strange at first if you are used to eating quickly, but it is essential for proper digestion. Also put your knife and fork down between mouthfuls, only loading up your fork when you have swallowed your last mouthful. This will give you time to chew properly and also slow down the rate at which you take on your food.
Eating too quickly often leads to over-eating as it takes 15 to 20 minutes for your stomach to register that you are full, so if you have eaten a large meal in that time you may not feel full immediately. It is also important to be relaxed when you eat as stress or anxiety can prevent proper digestion, so make sure you aren't working, watching tv, reading or multi-tasking whilst you are eating.