Become snobbish and arrogant asshole. Look down on those who consume junk food. Consider yourself to be above such lowly habits. This way you can social pressure yourself for your own betterment. You might make a few enemies along the way but if you're successful enough you might make new friends who are all equally obnoxious as you have become with your new attitudes. Surround yourself with those you aspire to be. E…
I am a former fatty who has kept the weight off for over a decade by developing an intense hatred and disgust for being fat. It's really the only thing that works long-term.
Hate yourself enough. It works[1].
[1]: One exception to this: do NOT try this approach if you are prone to depressive spirals with positive feedback loops - it could have the opposite effect. This approach is only recommended for people with normal serotonin and mood.