I'm one of those people! For the longest time I didn't drink coffee, I would get all my caffeine from soda... Then one day my doctor told me I was pre-diabetic and to stop drinking soda cold turkey. She said I should have coffee black or with a natural sweetener (not sugar; something like "agave nectar" is what she suggested). I tried it black and it was gross as fuck. I started putting a little milk in it. She said that was fine.
I reversed my pre-diabetes to no diabetes at all, so I started drinking soda again, lol. >_> I'll still usually have at least one cup of coffee a day though.