Yes you may need to take the thyroxine
for rest of your life.
However there are conditions where hypothyroidism
is temporary and in such cases you need to take thyroxine only for short period of time.
Following conditions require thyroxine for limited time.
Silent and postpartum THYROIDITIS
Acute THYROIDITIS etc.
As far as diet is concerned,there is no specific diet for hypothyroidism.
No foods have been shown to either improve the condition or make it worse. The best thing you can do is to eat a well-balanced diet, with plenty of fresh fruits and vegetables, minimal amounts of sugar and salt, and lean sources of protein.
However many people say that there are goitrogens containing food which interfere with production of natural thyroid hormone.
Goitrogens are naturally occurring substances in certain foods like broccoli, cauliflower, kale, spinach, radishes, soybeans, peanuts, pine nuts, peaches and millet. The good news is that many health professionals believe that cooking may inactivate these Goitrogens.