The acute hypersensitivity of certain children with autism can make some foods and food textures very difficult to chew, swallow or digest. Slimy-textured foods like pudding, jelly or Jell-O, or crunchy foods like carrot sticks, pretzels or crunchy-style peanut butter can be intolerable in a tactile-defensive mouth and palate.
These same children may gravitate toward a severely limited range of foods that are "safe" for them. This may cause alarm in parents and grandparents. A nutritionist or dietician may have recommendations and strategies to encourage your child to stretch outside their comfort zone by trying new foods; and parents should offer---not force---healthy alternatives.
So long as your child is not losing weight and will take a multivitamin in one form or another, he may try new foods on his own time, or grow out of his food rigidity as he ages. Beware, however, that some adults with autism have eating disorders for being forced to eat foods, as children, before they were ready. Others will gag or vomit at merely the sight or smell of certain foods, induced by the trauma in one so extremely sensitive.