[help] Lower values for a food type

[majuck]

I'm making a character that gets more benefits from meat type food, and less from veggies. 

I've already figured out the first one, but no matter how much I try to look, I can't find out how to do the second one, and most variants that I tried resulted with a crash.

I don't want them to be unable to eat it, I just want it to not give them as much hunger, health and etc., -0.25 for example.

This character is my first time coding, so I don't know how to write it myself.

I'll be thankful if anyone helps.