I have an under-active thyroid that makes my metabolism runs slowly. I take a daily dose of synthetic thyroxine and I will need to take this for ever. However, as the doctors don't know the long term effects of this, they tend to err on the cautious side and only give a dose that will bring your thyroid just into the 'normal' zone.
As part of my research, I have discovered that gluten can have a more severe effect on people who have an issue with their thyroid, and gluten sensitivity is not abnormal. I have got stricter about not eating foods containing gluten over the last few weeks, although occasionally I do still have something.
If I have piece of cake at church or a biscuit at a meeting, I have found that my metabolism slows down more, and it can take a couple of days to come back to normal. Someone asked if I ate items made with 'gluten-free' flour, but I tend to avoid them also. Last week at the weekly market I attend, one of the ladies had made some gluten-free shortbread after I stopped buying her gingerbread men, so I felt obliged to buy some. A big mistake - the reaction was much the same as eating a regular piece of cake, so something else to avoid.
I have found that giving up grain based foods is not that hard, but you need to be organised, and plan ahead. I make pots of soup that I freeze in portions for when I need a packed lunch, and we eat a lot of lunchtime salads. We don't keep cereals in the house, and it is only the children that eat bread - and a loaf will last a couple of weeks.