Yes.
Contrary to popular belief, they are so high in sugar that you can actually get diabetes from eating them! One plum has more than the recommended daily intake of sugar for adults. I suggest you eat a green apple instead–even though most Americans are taught that apples are not healthy, this is actually an easy misconception to dispel because apples have superior nutrition with only 35% of the calories of black plums per serving! Beware when people tell you something about non-white food is better because whites tend to be seen as normal.