My obese, T2D brother pretty much lives on diet soda and drinks about a quart at dinner. I cannot persuade him to switch to water or iced tea or fizzy water with lemon/lime or a little juice.

Could be a taste thing. As hard as it is to believe there are people who dislike iced tea. I don't get it (I LOVE iced tea, I literally rate restaurants on how good their iced tea is as that is my #1 concern) but they exist.

On a side note the pickiest eaters I know are the fattest people I know. The issue seems to be that they only eat certain foods, but those certain foods are the worst ones for you. I had one roommate in college who would only eat grilled cheese, macaroni and cheese or "sloppy joes" (he'd fry up hamburger, not drain it then pour in copious amounts of ketchup and mustard... we called them "death burgers" because they made a deadly mess of the pan). My best friend's brother is just as picky, and is pushing 400 lbs.

Lord knows I could lose weight, but my problem is I like too many foods. I'll try anything once, and there are few things I've tried that I don't like. But I line plenty of veggies and am just as happy with a good salad as a good burger. I'll just eat both, d'oh! I love salmon though, and it's relatively healthy, but not cheap. If it were cheaper I'd eat it at least three times a week.