Girth Gains

What is a good way to focus on Girth gains during the jelq process, and does diet play a role in the health of my penis?

I can assure you that eating healthier will make everything your body does (namely repair itself) faster and better. Since the goal of jelqing is to stretch and then have the penis repair itself, eating a healthy diet will help in a way.

By healthy diet I mean fruits and veggies, whole grains instead of bleached white bread, chicken, fish other lean meats, tofu (if you have a store that actually sells good tofu), while being sure to cut out processed sugar, corn syrup, and fats.