Well, it's helpful to focus more on ourselves at that time. Normally this person's weight problem has arisen due to desire. Have you ever had a desire that you felt was very strong? How did it feel? Did you feel you had so much power at that time? Rather then focusing on the other person and their lacks, it might be helpful to remember our own, so that we remember how it feels to have a desire that is out of control. Perhaps they may have a weakness in this area, but maybe not another weakness that you have. At least a person who is just having a food desire is not actually harming others at that time.
This may help you to have a little bit more compassion. And this other person may need a little bit more compassion for themselves, too. They may have a very busy life and don't have enough compassion to take care of themselves. How does it feel, when you don't have compassion for yourself? It doesn't feel very good, does it? So learning how to have more compassion for people, trying to consider what it is like for them.