I might be wrong with this but I think that a weight of 51 kg for 83cm is unhealthy.
I am not a doctor or expert at this though.
I think being that skinny might result in you having less energy and motivation to do certain things than "normal people", maybe also more "health fragility."
I used to be very skinny and not be hungry as well. That changed, once I forced myself to eat more than I wanted to.
Pretty quickly my body adjusted and started to demand more food.
Now my weight is at a healthier level.
I am not an expert at this. I would suggest that you should maybe go to your doctor or to an expert and talk with him/her about that issue.
Wish you all the best:)
