I dont think its malnutrition but I have the same problem, I eat perfectly normally. But have lost 5 pounds over the last 3-4 weeks. I am stable now but, all of my (little) body fat gathers around my ower gut which means that you can often see my ribs when Im relaxed which isnt a good look, Im trying workingout to help bulk up and look less starved so, give it a try 