The Bible warns us against gluttony (overindulgence in food or drink) -- which is the cause of most obesity. The writer of Proverbs declared, "Put a knife to your throat if you are given to gluttony" (Proverbs 23:2).
Why does the Bible warn us against this? One reason is because if we don't look out, food (and the pleasure it gives us) can easily become the most important thing in our lives. As someone has said, instead of eating to live, we end up living to eat. Self-indulgence of any kind is spiritually dangerous, for only God deserves to be first in our lives.
But God also wants us to take care of our bodies -- and we aren't doing that if we eat too much. The dangers to our health from overeating and obesity are well documented, and we need to take them seriously. The Bible says, "Do you not know that your body is a temple of the Holy Spirit, who is in you...? Therefore honor God with your body" (1 Corinthians 6:19-20). Is this your goal?
No doubt your wife loves you and wants what's best for you, but in an even greater way, God loves you and wants what is best for you. Don't turn your back on Him, but turn to Jesus Christ and invite Him into your life. Then ask Him to help you deal with your weight, as you submit to His will every day.