I perennially receive questions about feeding cats. People continuously pose, online and in my practice, all manners of enquiries about cats and food.

Some examples include: Can cats eat human food? Answer: Some foods yes, some foods no. What is the best food? (The jury is out and in my opinion there certainly is no one brand that is definitively the best, but generally it is likely that low-carbohydrate, high-protein foods are better than foods that pack carbs in.) Which is better: wet food or dry? (The evidence currently favors wet.) Is there something wrong with pet food in general that is impacting feline health? (I believe there is, but I can’t prove it. Feline idiopathic cystitis and urinary obstruction often respond to diet change, so I suspect something is wrong with mainstream diets that is contributing to the conditions.)

One specific question will be the topic for this post. It is a question that has been asked to me countless times. Cat owners want to know exactly how much they should be feeding their pets.

A modest amount of soul searching should reveal that most people already know the answer. It is the same in cats as it is in humans.

Cats should be fed a quantity of food that causes them to maintain a proper body weight.

Here is the rub: That quantity varies tremendously between individuals, and it also may vary tremendously in any individual at different life stages.

I will draw upon a personal example. When I was in high school I had a friend who worked at McDonald’s. I will never forget the day that he sent me hundreds of McDonald’s Monopoly game pieces. All of them were pre-scratched and were winners — they were good for hundreds of meals and drinks. I, and several of my friends, enjoyed free lunches for months. And make no mistake, those lunches were garbage. On one particularly notorious day I remember consuming four Big Macs in one sitting. And I remained thin as a rail.

If I were to eat in that way now, I would not only be sick to my stomach every afternoon. I would be obese. Like so many people, my metabolism slowed when I reached adulthood. I therefore had to adjust my caloric intake to avoid gaining weight.

Cats also generally experience different metabolic rates during different life stages. Young, growing cats have high metabolisms. Kittenhood obesity is not yet epidemic in our feline companions. However, adulthood obesity becomes a huge problem after the age of two, when many feline metabolisms slow.

Different individuals also have markedly different activity levels and metabolisms. Back during the McDonald’s binge days, I stayed thin because I luckily had a naturally high metabolism. My buddy who competed on the cross country team stayed thin because he ran many miles each day. A couple of my other less lucky and less active friends gained a noticeable amount of weight.

There are formulas that purport to identify the amount of food that should be fed to a cat, but they’re hogwash because they don’t account for differences in activity and metabolism. Furthermore, they don’t account for higher metabolic rates in lean tissues compared to body fat. The formulas are based on body weight, and they recommend increasing calories as body weight increases. Therefore, if you over-feed your cat, he will gain weight and the formulas will recommend feeding even more.

Most brands of cat food include feeding charts. These, again, are based on body weight and can lead to a positive feedback cycle as obesity sets in. Also, I have never seen a feeding chart on a package of pet food that failed, in my opinion, to recommend gross over-feeding. And let’s face it: There is an inherent conflict of interest. More food fed means more food purchased.

In reality, only one method will consistently lead to feeding the appropriate amount of food to a cat. That method boils down to trial and error. Start off with an amount of food that seems reasonable (perhaps reduce the amount recommended on the feeding chart by 40 percent, and use that as a starting point). Then monitor your cat’s weight for a few weeks. You can do this by purchasing a baby scale and weighing him regularly, or you can monitor it subjectively. A cat whose weight is ideal will have palpable but not visible ribs and a palpable but again not visible spine. When viewed from above he will have a small waist between his ribs and his hips. Learn more about assessing a cat’s weight here and at Catster’s story “Fat Cat Epidemic: 5 Signs That Your Cat Is Obese.”

If your cat is gaining weight or becoming subjectively too heavy, then decrease the amount of food you offer by 10 to 15 percent and monitor for another week or two. On the other hand, if he’s getting too thin then increase the food.

It’s not rocket science, but it takes dedication, and the process is always ongoing. And, in the end, it’s the only method that works.

Read more on cats and health:

• 5 Things I Did Wrong When I Took My Cat to the Vet
• 7 Vets Who Are Absolutely Making Fun of You
• Is Preventive Vet Care for Cats Really So Strange?
• 11 Cat Emergencies That Need Immediate Veterinary Attention

Got a question for Dr. Barchas? Ask our vet in the comments below and your topic might be featured in an upcoming column. (Note that if you have an emergency situation, please see your own vet immediately!)