Your comment that "Cognitive Therapy tends to look at anxiety (and other affect) more as a result of cognitive processes than as something which has a function of its own" caught my attention. I come from a Gestalt background and tend to view affect as the impetus to behavior. I believe that affective and cognitive processes are inseparable elements of a whole system; both impact each other and really cannot be separated into cause and consequence. With that said, I would like to offer my thoughts based on the limited information I have of your client.
It seems to me that anxiety and worry are functional responses for a person who grew up in the critical and gender biased household described in this case study. Gary's mother is "down on men" and she taught her children to feel the same way. Gary's father also seems to subscribe to this belief system since he is critical of Gary and is himself a workaholic -- perhaps in an attempt to prove his own value, to his wife and himself. In these circumstances, Gary's anxiety would be a response to his lack of self-esteem and lack of self-worth -- his feelings of not being good enough. He was told that he could do nothing -- his sisters had to do his papers for him for school; and that, beyond this, he, himself, was nothing, a mere man with no value.
The secondary gain which I see in his responses of anxiety and worry is that he is able to maintain a place for himself within his family system. It is a means of buying into his mother's belief system, that men are incompetant. He has proven his competance time and again in getting through medical school and performing well at his job; his anxiety and resultant Irritable Bowel Syndrome allow him to be the defective male his mother expects him to be. Additionally, it offers a way to identify with his emotionally distant father, in whose footsteps he seems to be following; a hospital administrative position seems to be a choice for longs hours and little recognition. As we follow this case, I wonder if we won't find that Father is also afflicted with constant anxiety and worry. Finally, it may also get him care and comfort from his girlfriend. He ascribes her the role of bolstering his self-confidence, and I get an image of a woman who carefully and constantly reminds him of his value. In doing so, she enables him to continue to denegrate himself; he has no need to generate his own self-confidence and self-worth as long as she fulfills this function. And he must continue to need her to care for and comfort him -- thus, to feel this anxiety -- in order to receive these services. What type of relationship would they have were he to stop needing her to build his self-confidence? What role would she fill? How would they achieve intimacy?
I will be interested in following the progression of this case to learn how a Cognitive Approach might address these issues, even though they may not be approached in the manner I have outlined here.