What is bad for diabetics is to have high BG. whether a food is bad or not depends on what it does to your BG. We do know that carbohydrates raise BG. ALL carbs raise BG. how high depends on what you eat, how much you eat and YOU. every one reacts different to carbs.
black beans are about 25% carbohydrate
eggs have virtually no carbs
Milk has about 12 gr of carbs per cup.
the only way to tell if a food is good for you or not is to test before you eat and test 1 hour after you eat. the difference in BG is what the food caused.