It has been a while, but I've always understood the theory to say that the superego, the internalization of values and rules, can cause us to repress ideas that aren't inline with our values. Basically, as we continue to do things that we 'know' are 'wrong' there is a resultant feeling of anxiety, which we often seek to avoid.
There are better ways to explain this type of phenomenon though; I would suggest some basic cognitive behaviourism. For instance, if we suggest that a person's thoughts of guilt, let's say around exercise, create a punishing effect, then we can in turn come to associate exercise with the negative feeling of guilt. If we expand out and include the further associations of obesity/guilt and their close association with exercise, we can start to build a theoretical model of why neurotic behaviors develop around exercise.
I'll do a quick edit to respond to the a comment about sources. I was doing some research after I posted this, I managed to find an article discussing how attitudes relate to the avoidance of exercise:
I'm having a harder time finding anything specifically talking about exercise and the types of avoidance/escape you see in high anxiety behaviour. Here's an article talking about how avoidance and escape can serve as reinforcing mechanism for phobias: