There is an obesity epidemic in USA. Just because we are transgender, doesn't mean we are immune to all the other diseases that affect Americans. While 656 pounds is extreme, it is not unheard of. This has happened to others, regardless of their physical sex or gender status.
I am a 100+ pound loser and you can do this as well. Diet and exercise are how I lost the excess weight. Others have resorted to bariactic surgery.
Natural foods, especially fruit and vegetables are your best friend. It is really hard to overeat on vegetables.
Calorie dense fast food and processed foods are you worst enemy. There are a lot of hidden calories that many of us did not know were even there.
Comfort foods are just as bad. Are you eating because you are truly hungry or are you eating to relieve stress?