The short answer: It depends.
The long answer: Cats are obligate carnivores, so their diet must consist mainly of animal-derived meat in order to stay healthy. They can enjoy snacking on certain vegetables occasionally, as long as these are prepared properly. Gary Richter, DVM tells Rover, “Pet owners can always try to give vegetables to cats in food or treats. Not all will eat them. There certainly are good nutrients in vegetables when part of a balanced meal.”
Cat-friendly vegetables include broccoli florets, carrot, celery, green beans, green bell peppers, peas, pumpkin, spinach, winter squash, and zucchini. Meanwhile, do not feed your cat garlic, mushroom, onion, and tomato as these are considered toxic for them.
To be on the safe side, go through ASPCA’s list of toxic and non-toxic plants before introducing a new vegetable to your cat.
How to feed vegetables to your cat: Do a quick check to find out if the vegetable is safe for your cat to eat. Wash your chosen vegetable thoroughly. Take out the hard and inedible parts such as the core, seeds, and stalk, then cook it without artificial flavourings or seasonings such as salt or sugar. You can boil, steam, blanch, or grill the vegetable, making sure it is soft enough for your cat to chew.
Conduct a trial test by giving your cat a tiny piece of the vegetable. Take note of any body or mood changes in the next 24 hours.
What to do if your cat accidentally eats a toxic vegetable: If your cat ate something lethal for her, she may manifest any of these signs: diarrhea, depression or coma, difficulty in breathing, skin inflammation or swelling, salivation, shock or collapse, twitching and fitting, vomiting, and/or changes in drinking, urinating and appetite. If she displays any of these symptoms, call your veterinarian immediately.
In summary: Vegetables can be given to cats as treats or mixed into their meals once in a while. Remember that cats need to consume protein to meet their daily nutritional needs, so vegetables should never be used to replace the meat in their diet. If you want to introduce certain vegetables to your cat, make sure to get your veterinarian’s approval beforehand.