Whenever my cats get a change in diet (like from pellets to canned, or from regular to organic, changes like that in my pursuit to keep them healthy), they absolutely refuse to touch the new stuff at all. But after 3 or 4 days of literally starving, they always seem to miraculously change their minds. It takes will power on my part to 'allow' them the time to reconsider their preferences.
The last change a few months ago from dry pellets to canned wet food was the most difficult. It took several days and they were adamant about not eating canned food. But....hunger won out in the end, and now they dont' even care much for pellets at all and they just love the canned food that they despised before!
Funny what actual hunger will do for an appetite.

I have several friends with grossly obese cats who tell me their cats 'hardly eat anything' and they can't imagine why they are so fat. Then I see that they have GIGANTIC bowls brimming with pellets set out and they admit that the bowls are out and available 24 hours a day....but that their cats "really don't eat that much"!
Of course the cats are always waddling about like grotesque walruses during this discussion and can barely even clean or groom themselves anymore they are so fat.
Putting out 24-hour-a-day bowls of pellets is a recipe for obese cats.

Underweight elderly cats are a different problem altogether though.