I hava a Franchise zoo with around 3500 guests and around 100 animals.
As already above explained, the food costs were only a visual bug. I had a l good running zoo (around 4 million and earning tons of money with all guests super happy), and after the patch the money just went down and down. I checked where I loose money and it was on one side the refunds (check the education heatmap - every red spot makes guests unhappy, even if the overall guest happiness is green). On the other side I hadn't had enough shops at the right places - so everywhere something was damaged, I checked the guests thoughts and normally they were all thirsty or hungry, so I changed the locations of the drink shops and added more drink and food shops (and enough vendors!).
As well some minor problems (queue at the ride too long, some staff trained way too much, so too expensive as well) and too many water and energy facilities due to bad layout planning - I do not say that anyone else is doing a bad layout planning, that just might be my personal stupidity ;-)
The most thing that helped me was to reduce the amount of animals like Gorillas or Giant Pandas - I had a habitat with around 12 Gorillas...
So in the end it was way more management to do, and took me some hours to get back to earn money again

The zoo is running good now, and it was nice doing the management even if that's not what I normally do that often (I prefer creating ;-) ...).
I understand the frustration if you have a zoo build in a lots of hours and suddenly it runs bad, but on the other side, the management part of the game is way deeper than in other games.
I hope you all enjoy the game nevertheless and find a way to get your zoos back to a good state