If your thyroid gland has been entirely ablated by radioactive iodine or removed by thyroid surgery, then this advice is true for you. On the other hand, for the large majority of thyroid patients who still have a functioning thyroid gland you may not need to take meds for the rest of your life. However, this needs to be discussed with your Dr. in detail. Do not stop taking your medication without Dr. approval.
In general, for thyroid health...
For weight loss, it's the same rules as those without thyroid issues, yet might be a bit more of a struggle. However, if providing your body the right nutrients (read above articles) and follow other healthy lifestyle habits you can lose weight.
Here's a good places to start: