Plant eating prevention

Do you guys have any solutions to stopping a cat from eating and nibbling on the plants? I'm afraid he may be getting sick because of it and my mom doesn't want to put any type of substance on it because she doesn't want to harm them, so nothing's working as far as trying to keep him away. Any ideas?

I've had to slowly get rid of even my FAKE plants and trees because I have one or two nibblers.  Sammy ate a prayer plant which is harmless.  Actually some green is good for them.  I assume (and I know you should never assume) that since they are eating it that they must need something in it.  Maybe fiber?  I don't know.  One time I purposely got spider plants for them to nibble on.  They wouldn't leave the thing alone anyway so I would bring one in and by the next morning it looked like a pineapple.  I mean they all LOVED that thing!  It didn't hurt them.  No diarrhea, and they seemed to eat less at meal times (they are overweight from being indoors) so that was a plus.  I didn't keep it up because I had to grow my own.  I'd cut off the babies on the ends and replant them outside at my front door and let them grow and transfer them to bigger pots.  Wanted to save money that way and it was very cost effective.  But once winter time came, I stopped.   

I don't really know of a solution to keep them from eating plants.  Mine do not like the cat wheat grass.  I'd just give them something that they can eat safely.  Check out this site: 

http://www.aspca.org/pet-care/animal-poison-control/toxic-and-non-toxic-plants