I don't buy that there is a strong correlation between sugar consumption and porn use, but there is a strong correlation between willpower and healthy habits.

Any healthy habit is going to require some amount of willpower to put into action. Walking, running, going to the gym, lifting, etc. all require some willpower to start. After you've started, there is a need for willpower to keep going (not stopping after X miles, doing one more set, rep, etc. [when it comes to lifting heavy weight, people also have to learn how to harness their willpower to lift more than their brain believes is possible]). Eating well is the same way - I'm going to stop eating now, I'm going to make my food from a whole source, I'm going to pass on the Oreo's, etc. I've known several people who trade one healthy habit for another, they'll start to eat well, but then will stop going to the gym, or who will start going to the gym, but then their diet goes to pot.

Lots of people believe and teach that willpower is a limited resource that you build just like a muscle. If you burn out your willpower in one aspect of your life, you won't have willpower to do or not do something else. However, like a muscle, by practicing willpower on a daily basis, you can develop the ability to exercise more willpower.