"You are what you eat" is a solid piece of common sense that is just as true for your cat as it is for you. Feed your cat a quality diet, and you're more likely to have a healthy cat.

The pet food industry is big business -- and with good reason. There are well over 100 million dogs and cats living in American homes, plus who-knows-how-many more in shelters, catteries, and kennels across the country. To top it all off, you have thousands of people feeding strays. If you figure a single cat can go through some 90 pounds or more of cat food in a year, we're talking about hundreds of millions of dollars being spent annually, just to feed the kitty.

Just like human food, there are some tasty feline treats that are good for cats and some things that are basically junk food. An occasional snack of the not-so-healthy stuff shouldn't do any permanent harm but don't make it a regular part of your cat's diet.

The wild ancestors of the modern house cat were hunters -- an instinct your cat still has. Whether Tabby is bringing you gifts of demised birds and mice or pouncing on a piece of lint, she's expressing a powerful natural drive to stalk and kill prey. If you doubt that your cat is a natural-born meat eater (and predator), just take a good look at her teeth the next time she yawns. Those fangs are not designed for eating alfalfa sprouts.

The fact is your cat is so much of a carnivore, she can't survive as a vegetarian. There are certain nutrients found only in animal proteins that your cat needs. One of these nutrients is an amino acid called taurine. Without taurine, cats can go blind and develop enlarged hearts, which will likely give out on them well before their time. And unlike dogs, cats require a dietary source of vitamin A and a fatty acid called arachidonic acid found only in animal tissue. That's why you should never feed dog food to your cat. Dog food just doesn't have enough of the right kinds of nutrients for cats. By the pound it may be cheaper to feed dog food to your cat, but it could cost your cat her health, her sight, or even her life.

Of course, that doesn't mean you should feed your cat raw meat or let her depend on hunting as her only source of food. It's been hundreds of years since cats lived in the wild, so their hunting skills are more than a little rusty. Plus, cats that hunt or eat raw or undercooked meat can pick up several kinds of diseases -- including some that might get passed on to you.

If it's green and it grows from the ground, the odds are some cat will try to eat it. This vegetarian quirk in the carnivorous cat's personality is particularly worrisome if the plants in question are your prized houseplants -- or worse, if they're poisonous to your cat.

Many cat owners look at plant eating as a behavior problem -- and it is if the cat is eating plants you don't want her to. Some folks assume that a cat who eats plants isn't getting enough of the right kinds of food in her diet. They're right, too -- but only in the sense that what the cat needs more of in her diet is...plants.

The experts have a few ideas why cats eat plants. It could be to get some trace nutrients, to help with digestion, or as an emetic to help bring up swallowed hair and other nonfood items. Whatever the reason, eating vegetation is an instinctive behavior in cats; you can't stop it. So the best thing to do is point the behavior in a direction you can both live with.

Plant a "cat garden." You can find ready-made kits in pet shops and catalogs, but a more economical choice is to just do it yourself. If you're handy, you might build a fancy container out of wood or you can just use something on hand. Whatever you do, make sure you plant your cat garden in a container that doesn't tip or move easily. All you need is just a couple of inches of good potting soil and some seeds. Oat grass or catnip are good choices. You might want to keep the garden out of reach from your cats while your "crop" is coming up, but once the greens are a few inches tall, set it out and let Tabby munch at will.

Get your plants out of reach. Cats are incredibly good climbers and leapers, so putting your houseplants on stands or shelves probably won't help much. Mantels, windowsills, and the like are easy landing pads for feline acrobats. Hang plants from the ceiling, put them behind cat-proof barriers (on a sun porch closed off by glass doors, for example), or set them in locations that your cat absolutely can't jump, climb, or crawl to.

Shield your plants. If you can't get your plants out of kitty's reach, try forming a protective shield around your plants. Placing chicken wire, plant markers, or even mothballs in the soil around your plant may safeguard it from prying paws, but these barriers aren't so pretty to look at. Try adding some Spanish moss around the base of your plant to keep your cat away. Sometimes, spraying bitters on the leaves will discourage a cat from chewing. Other times, though, putting some bad-tasting substance on a plant does more harm to the plant than the cat's teeth.

A well-fed cat doesn't need to snack between meals any more than you do. Too-frequent snacks will have the same effect on your cat that it can have on you: unhealthy weight gain and an imbalanced diet.

Of course, it's hard to resist the temptation to give your feline pal a treat now and then -- and it's perfectly all right to give in to that temptation, assuming there's a long enough stretch of time between now and then. How long of a time depends on your cat and the kinds of treats you give her. If your cat is still eating the recommended amount of a quality cat food every day and isn't overweight, then you're probably not giving her too many treats. If, on the other hand, your cat is chowing down on tasty but not-so-nutritious snacks and is either getting plumper or turning her nose up at dinner, it's time to change your strategy.

Store-bought cat treats tend not to be packed with good nutrition. Their main purpose is the same as human treats: to taste good -- real good -- and that's about it. "Gourmet" cat snacks usually have fewer artificial colors and fillers in them but still aren't meant to be fed as a regular part of Tabby's diet. The good thing about "gourmet" treats is the cost: They're usually so expensive that cat owners won't overfeed them to their cats!

A question vets hear all the time is, "Can I feed my cat people food?" There's very little that people eat that cats shouldn't (or won't), so that's not really so much of a problem. (Cat owners should be careful about feeding dairy products to their pets. Although cats love dairy products, many don't digest them well and may get sick.) The question once again is nutritional balance. Just like with home cooking, feeding your cat leftovers or using people food for snacks may not be providing her with the right nutrients in the right amounts.

Still, people food might provide some of the healthiest snacks for cats. If you give your cat some scrambled eggs or a couple of pieces of pasta, at least you know what's in it. And you might be surprised what your cat will eat. Cat owners report their pets begging for predictable tidbits such as fish and chicken as well as unexpected ones, including tomatoes and cantaloupe.

Your cat needs about an ounce of water per pound of body weight every day. That doesn't sound like much, but it adds up: An average-size cat would need two quarts of water every week.

Of course, cats get water by drinking. But there's another important source of water for your cat: the food she eats. The more water there is in her food, the less she needs to drink. Canned cat food is more expensive because you're buying water along with the food (up to 75 percent of wet cat food is water) and paying a little more for the container. Dry cat food has much less water (perhaps 10 percent by weight), which means a cat whose diet consists of only dry food has to drink a lot more.

Dehydration (not enough water in the body) is a serious problem for any living creature, and cats are especially prone to it. A cat can go without food for days, losing up to 40 percent of her body weight, and still survive. But a loss of body water of only 10 to 15 percent can kill her. Other liquids -- like milk, if it doesn't make your cat sick -- are a good source of water, but nothing beats the real thing. Be sure your cat has plenty of clean, fresh water available at all times.