I think it’s worth looking at what different facets are part of being autistic. It might be possible to differentiate between personality characteristics that are important to you (that you associate with your sense of self) and those that you can see as somewhat less essentially part of who you are.

For example, you might have a particular way of thinking that is different from other people which is both important to you and often associated with ASD. That doesn’t feel like something likely to change qualitatively from say a diet change.

On the other hand, there might be aspects like being overwhelmed by particular kinds of stimuli, that feel less personal and may feel more likely to be impacted be something like a diet change.

Finally, consider that you might be holding too tightly to some aspects of who you are “right now”, to be able to see and accept how some of these things might change. I know I do sp sometimes (regardless of whether I might be on the spectrum, or not). At the very least a relatively fixed (as opposed to growth) mindset is also often associated with ASD.