If UL has a true food addiction, reasoning might help but it's generally not that effective in fighting cravings. It's like telling a cigarette smoker that they'll get lung cancer in 30 years--studies have shown that those types of messages are completely ineffective. I think if UL is craving a greasy burger or fries or a pie, telling him to think of the joys of a salad isn't really going to help. To be honest, I'm a healthy eater and rarely eat junk food, and thinking about more energy isn't going to stop me from eating a piece of fried chicken if I'm in that mindset, which usually happens when my body is telling me I need more fat.
One good book to read (did someone mention it on this forum recently? I thought I saw it, maybe in the What Are You Reading forum) is The Power of Habit by Charles Duhigg. In it he explains the brain's process from cue to reward (or stimulus to response). Some self-defeating behaviors may simply be a function of learned responses that can be unlearned.
When I first read it I thought the idea that addiction is just a matter of breaking the habit loop was a bit simplistic, but it's certainly worth trying.