Let me assure you that God does want you to change not just so you'll feel better about yourself, but because He loves you, and He doesn't want you to be burdened with the serious health problems that usually accompany this condition.
This is why I hope you will take your doctor's warnings seriously and begin to heed his advice. He knows far better than I do what could happen if you keep ignoring this; he has seen it happen to others. If he has given you a suggested program of diet and exercise, put it into action. The Bible bluntly says, "Put a knife to your throat if you are given to gluttony" in other words, avoid overeating at all costs (Proverbs 23:2).
Be patient and don't get discouraged; it probably took you years to get into your present condition, and it may take time to see results. The Bible says, "A man's wisdom gives him patience" (Proverbs 19:11). Make a shopping list also and be disciplined when you buy food; avoid buying anything on impulse. Once something is in your freezer or on the kitchen shelf, it's probably going to get eaten.
Most of all, open your heart and life to Christ, and make it your goal to put Him first in your life. Yes, your physical health is important but even more important is your spiritual health. Give your life to Christ today.