Then regularly mention the things you value in her. Enjoy her touch of your body. Enjoy looking into her eyes. Enjoy touching parts of her body that don't trigger your reaction to her weight. Also, take over more of the household duties to give your wife additional time to take care of her appearance.
Body image is an issue that affects a person's sexuality.
How we feel about our bodies determines how readily and openly we are able to share them with our spouses. When there is a gap between how we view ourselves or our spouse and what we accept as an ideal body, we develop a body-image problem. To reverse that problem, we need to bring the actual and the ideal closer together. Most people have unrealistic ideals about weight and beauty because television and movie personalities have become the standard. Of course, these people have the help of professional makeup artists, video enhancement and sometimes even a plastic surgeon.