I’ve had this happen a couple times already. I had a drunkard for a recruit and after he lost one of the inventory items the game gave me a multiple choice. I chose the harshest of the choices which was to “whip him into shape”. This choice changed his drunkard attribute to where he was no longer a drinker.
If you carry to many rations then gluttonous recruits can become fat by over-eating, also recruits can start fat. To change this you need to carry less food <100. This will make sure you mercs do not over eat and become fat as well as making the fat mercs fit.
If your character is afraid then try raising his resolve to reduce the chances of being spooked.