It has been advised for years that drinking coffee alone as a single meal will take you somewhere you will regret. Apparently, we were never listening. Don't get me wrong, coffee has unbelievably positive effects to human health such as reducing the risk of sclerosis, and working as an antioxidant, it enables the body to take off body's free radicals--integral chemicals that cause cancer.
Relax, because we will never let any bad happen to you again. Listen and take note that these effects that will be applied to you once you take this for granted. You have been warned, you Starbucks lover.
These will happen to you, again, when you drink plain coffee on an empty stomach.
Hydrochloric acid (HCl) is present in the digestive tract of humans, and they are located at the stomach. With its interaction to a caffeine-rich coffee alone, it triggers production of more HCl's that will strike digestive system linings and may cause disorders.
One is indigestion.
Applying to real life, it is like a cyclist strolling around the park where he didn't bother to make a stopover. Looking at the context of passing water in the body, it will then constantly take off water from the body, causing dehydration.
...to your heart beat. There can be irregular pulse rate, thus affecting body's blood pressure.
Remember this. With that single mistake, you can suffer as tragic as experiencing withdrawal and mood changes. You can then be eligible for a monologue. Great.
Eat something else, dude. Or if time or resources don't permit, make sure some dairy stuff will complement your coffee--butter, creamer, milk. Your call.