The instant ones will have milk powder added (the water is just to hydrate it), so the non 'diet' ones will be high in fat, too.
The thing is, chocolate is not intended as a health food?. It is a high fat, sweet food, which a lot of people enjoy, and I'm sure we all know that.
It is so wearing when everything that gives pleasure is accompanied by a lecture on how bad it is, as though we are children, rather than 'ladies of a certain age'. By this time of life, most of us will be firmly in one camp or another - the 'no treats' camp, the 'bring it on, I'm going to enjoy life' camp, or the 'all things in moderation' one, and no amount of dark warnings about fat or sugar content will shift us.
I make no apology for enjoying my velvetiser, unnecessary as it is, and as unhealthy are the drinks it produces?. I use it when friends come over as an alternative option to tea or coffee, and it is very popular - I always have to check that I have enough milk in before offering, as most people choose the chocolate.