Maybe they should try the special: Soup Yasai Jinkot.
Edit: Also, eating fiber and protein first and saving starch and carbs for last is good advice. It also makes you more likely to feel first faster, so you don't pig out on empty calories like carbs and sweets, and then eat the fiber and protein later, which the stuff that actually makes you feel full.
Also, the "cheat day" every 2 weeks or so is also a good idea, as otherwise your body will lower its metabolism to keep you heavier and burn less calories in case of "lean times" which was more of a thing back in the old days, when food scarcity was more of a thing. And just like the comic says, cheat day doesn't mean you pig out, just that you eat more than you normally do while dieting, with maybe a few "bad foods" that you don't normally eat anymore.