Eating is high up on our list of occupations as people. When you are unable to eat, it can be very detrimental to your life.
There are many reasons why a person can’t eat. It could be caused by oral-motor problems where the muscles of the mouth don’t work very well. Another cause is sensory, where something about the food is very negative. The sensory problem can be related to texture, flavor, or smell, or a combination of many things. When working with sensory problems, there are many stages to go through. You have to do some oral desensitization, then transition to different textures such as starting with solid foods if they are only drinking, and then transitioning to lumpy foods.
Another cause of food aversion is physical pain. The pain could be caused by severe reflux or mouth sores. Some children have such tiny stomachs that they are physically not able to eat much, and some have slow stomach emptying so they are full for a very long time.