do we make Bracha on something that is unhealthy, like food that is not healthy at all?

We do not make a bracha on food that is forbidden to eat, according to the halacha, like pig (Shulchan Aruch 196,1). However, we do make a bracha on unhealthy food like Coca-Cola and chocolate bars because it is permitted, according to halacha, to eat unhealthy food (see in Minchat Asher: part 1, chapter 135). In a case where the food is extremely unhealthy and can cause damage to the person's health, i.e, someone who suffers from severe diabetes and by eating a sweet food like a piece of cake he is getting himself into danger, simply should not say a bracha. Some poskim say that he should say a bracha because one crumb would not cause any damage. So he has to make a bracha over the crumb which is not forbidden to him (Rav Elyashiv, 'Kav V'naki': 62, but see Harav Shteinman's opinion in the approbation to the book 'Kav V'naki') . In conclusion: Yes , we do say a bracha over unhealthy food.