I'm thankful you want to do something about your weight, because obesity is a serious issue today -- much more than it was for previous generations, including those in Bible times. And it's not just a matter of our appearance but of our health -- which is definitely of concern to God.
The Bible reminds us of two important truths in this connection. First, it reminds us that God gave our bodies to us, and we aren't to misuse or abuse them -- because when we know Christ they actually belong to Him. Instead, God wants us to bring honor to Him with our bodies, and one way we do this is by taking care of them. The Bible says, "You are not your own; you were bought at a price. Therefore honor God with your body" (1 Corinthians 6:19-20).
The Bible also reminds us, however, that overeating (or what the Bible calls "gluttony") is a sin in God's eyes. It harms our bodies, and it also harms our spirits, because food becomes more important than it should, and can even make us insensitive to the needs of others. The Bible says, "A companion of gluttons disgraces his father" (Proverbs 28:7).
Ask God to help you get the exercise you need, and to eat in a healthy way. Most of all, however, take steps to focus on something that's even more important than your physical health -- and that is your spiritual health. Take time to feed your soul every day with a steady "diet" of Scripture, prayer and Christian fellowship.