Cat eats *way* less than package recommends... but has gained weight

I've had my cat Abby for less than a year. She's a rescue, estimated age 8.

I've always just filled her food bowl whenever it was nearing empty, but my partner noticed that she's gotten kind of chubby. She's 9 1/2 pounds, which for her size is a bit overweight. I didn't want to put her on a diet, but decided to start feeding her only as much as the food package recommends.

But I noticed she eats way less than that! She eats about 100ml of dry food a day, and the package recommends 125ml for a cat who's only 4 pounds! For a cat her size, she eats only HALF of what the package recommends.

I tried a different brand of food and she ate 105ml, which is about 65% of what the package recommends for her size.

Part of me is worried that my cat is underfed and undernourished, and the other part of me is disbelieving because she's gained weight since I've gotten her and is a little chubby.

Does anyone know if this is at all normal? Do cat food packages typically overestimate how much a cat should be eating? How is it possible my cat can be both underfed and overweight? Should I be worried? 

I know that in the U.S. the feeding guidelines on pet food is typically high.  Does the packaging include calories.  Typically a kitty needs 20 to 25 calories per pound of their ideal body weight per day to maintain weight.

Thank you for your reply! I did the math, she's eating about 165 calories.

"Typically a kitty needs 20 to 25 calories per pound of their ideal body weight per day to maintain weight."

That would be 8.25 pounds (at 20cal/lb) or 6.6 pounds (at 25cal/lb)

I don't know her ideal weight but I would guess about 8 1/2 pounds? So according to your formula she is under-eating, but not as extreme as I thought. Still, it's strange she'd gain weight.

We live in an apartment building so she's an indoor cat. She does like to play but also loves to sleep so doesn't get much exercise.

It depends a lot upon the food itself. Dry? Wet? Brand? Nutritional balances of protein, fat, carbs?

Too many carbohydrates could be the culprit. Not getting exercise can lead to weight gain as well.

Plus, just like people, some cats just have a lower metabolism than others.  I have a 15 lb cat who eats about the same amount of food as his 9 lb brother.  If the 15 lb guy eats any more, he gains weight

She's also at an age where cats typically do gain a bit of weight. If it isn't excessive, this may not be a bad thing. Once cats reach age 12 or so, they tend to start losing weight, and if they were thin to start with that doesn't serve them well in their later years. Living creatures change throughout their lives, they don't stay exactly the same (in weight or calorie needs or anything else).

"What happens to daily energy and protein requirements for cats as they age? Well, it turns out that maintenance energy requirements decrease as cats mature and become middle-aged (4-9 years of age), explaining the tendency of many cats to gain weight during this time (17,18).

However, energy requirement sharply and progressively increase again in these cat when they become older, starting at 10 to 12 years of age (17-19). If daily caloric intake is not increased, progressive weight loss will result, due in large part to the loss of lean body mass (i.e., muscle mass), a phenomenon referred to the “sarcopenia” of aging (20-22)."

from here: http://www.endocrinevet.info/2011/11/optimal-protein-requirements-for-older.html (under the heading "Dietary Protein Requirements for the Senior or Geriatric Cat: What Do We Know?")

is she lazy? My calico is laaaazzzyyy. She's 12 pounds. A little chunky. But she eats the same as our 9 pound cat. I try to play with them. The calico, Gretchen, just bats at the string/toy. Lazy butt. While Lexi jumps around excited. I'm still trying to find ways to get G excited about play.