First up is coffee, the reason to avoid this is due to its caffeine and its interaction within the body. when we consume caffeine it acts on the sympathetic nervous system (known as fight or flight system) one of the actions of the sympathetic is to release hormones to inhibit salvation (our body's initial digestion process) as well as inhibit our digestive activity in the intestines.
This will in turn reduce the amount of time food has in our digestive tract, and giving digestive enzymes less time to act upon and break up and absorb the meal we have just eaten. This will become apparent for some as I'm sure many of you are regular in the mornings after your cup of joe :)
Up next are carbonated/fizzy drinks. these also generally contain caffeine as mentioned above cause it's own problem. the other problem with them is that they contain a large amount of gas, this when drank causes the stomach to expand putting pressure on the walls and inevitably forcing our food through into our intestines before it can be properly broken down for enzymes to act upon them.
Without proper breakdown, digestion, absorption and assimilation we cannot get the nutrients our body needs to function properly.