Vets explain how to tell if your cat is overweight or underweight — and why it matters for their health

• Overweight cats may have a cuddly appearance, but they also have a higher risk of health concerns.
• Vets recommend using the Body Condition Scoring chart to check your cat's size and shape at home.

Overweight or "chonky" cats might star in any number of memes and viral videos, but gaining too much weight can put your kitty at risk for a number of health concerns.

Excess fat can:

• Lead to health issues like arthritis, diabetes, and urinary tract infections
• Increase their pain levels
• Affect their ability to run and play
• Shorten their lifespan

Up to 60% of cats in the United States are overweight or obese. But you might not always find it easy to recognize the difference between a larger breed of cat and a cat with obesity.

Here's how to check your cat's size under all that fluff, plus a few tips for helping them lose weight safely, according to veterinarians.

What's a healthy weight for cats?

A healthy weight depends on feline breed and body frame size, and there's a lot of variation between cats: Some breeds, like the Siberian, might weigh 26 pounds. Others, like the Munchkin, might only weigh 5 pounds.

Body Condition Scoring (BCS) is the best way to check your cat's weight, says Angela Topf, a veterinarian at The Vets.

The BCS chart provides healthy weight guidelines for pet parents and veterinarians by breaking down a cat's potential weight into several categories:

• A score of 1-3: Under ideal weight. If you have a short-haired breed, your cat's ribs might be clearly visible. You'll feel their ribs more easily, and you'll notice a clear dip in their waistline right before the hips.
• A score of 5: Ideal weight. You can feel your cat's waist and ribs, but subtle, healthy fat covers their ribcage.
• A score of 7-9: Over ideal weight. You might notice an excess fat covering or a lack of waistline on your cat. You may have a hard time feeling their ribs, and their abdomen might seem rounded.

Each score above 5 indicates a 10% increase in body fat, says Julie Churchill, a veterinarian and professor of veterinary nutrition at The University of Minnesota College of Veterinary Medicine.

Obesity typically means a cat weighs at least 20% more than their recommended weight based on their breed. That means if your cat has a BCS score of 7, they have 20% more fat than what's considered healthy for that cat's size and breed.

However, it's important to note that BCS is to cats as BMI is to humans. In other words, it's not always an accurate measurement of obesity.

In fact, a BCS score between 6-9 is considered healthy for certain cats. For instance, older cats often can't get nutrients from their diet as effectively as they age, so they might need more food to get enough vitamins. This can translate to a higher weight.

Why do cats gain weight?

Of course, if you're constantly feeding your cat treats and lots of food, they'll probably gain some weight.

But plenty of other contributing factors can also play a part:

• Medical conditions: Hypertension and hypothyroidism can both cause weight gain in cats, Topf says. These conditions may also increase your cat's risk for cardiovascular disease, which can make physical activity more difficult and indirectly lead to weight gain. That said, hypothyroidism very rarely affects cats.
• Spaying or neutering: One 2021 study found that more than half of neutered or spayed cats examined were overweight. Spaying and neutering may slow down your cat's metabolism. Of course, this doesn't mean you should avoid spaying or neutering your cat — just that it's important to determine the right diet to maintain their weight.
• Breed: Another study on overweight and obese cats noted that domestic shorthairs were more likely to experience obesity than other breeds, like Persian cats or Norwegian forest cats.
• Dry food-only diet: Evidence links a diet without wet food to an increased risk of obesity and diabetes.
• Lack of activity: Cats who live primarily indoors are also more likely to gain excess weight, due to a lower activity level and less excitement in their environment to get them moving.
• Free feeding: Keeping your cat's bowl full all the time can lead to weight gain for cats who graze even when not hungry.

Health risks for overweight or obese cats

Weight gain increases your cat's risk of a number of health conditions, since extra body fat increases their inflammation levels, Churchill says.

An overweight cat has a higher risk of:

• Arthritis
• Urinary tract infections
• Vision problems
• Diabetes
• Skin conditions like eczema
• Musculoskeletal issues
• Asthma and allergies
• Digestive issues like diarrhea
• High blood pressure

An obese cat may have a lower activity level, a reduced quality of life, and a shortened life span, Churchill adds.

What about underweight cats?

It's less common for cats to fall under the ideal weight range: A study of 15,659 cats found that only 5.3% were underweight.

That said, an underweight cat has a higher chance of experiencing health risks like malnourishment. What's more, rapid weight loss can sometimes suggest medical concerns like viruses, parasites, or cancer.

Factors that may raise your cat's risk of a too-low body weight include:

• Having medium length or long hair
• Not getting neutered or spayed
• Older age
• Illness
• Being purebred

Note: A veterinarian can offer more guidance and feeding recommendations if you think your cat may need to gain a pound or two for optimal health.

How to help your cat safely achieve a healthy weight

"First and foremost, you should take your cat to a veterinarian to assure healthy slow weight loss," Churchill says.

Churchill recommends always checking with your vet before cutting back your cat's food or switching brands — sudden or major changes to a cat's diet could lead to malnourishment,

"The calories in cat foods can vary widely, so if you change foods, one cup likely will not be the same amount of calories," Churchill says.

What's more, losing weight too quickly can raise your cat's risk of diseases like fatty liver, Topf says.

"Weight loss should take place over weeks to months, at a rate of 0.5%-2% of their starting weight per week," Topf says. For instance, a 20-pound cat can safely lose just under half a pound a week, but no more.

Your veterinarian may recommend the following tips to help your cat lose weight:

• Outdoor playtime: Walking and playing outside helps your cat get more physical activity. Just note it's safest to do this by taking your cat out on a harness to reduce their risk of injury, unless you have a fully fenced backyard or other enclosed space. You'll also want to consider treatments to prevent fleas and other pests.
• Monitoring their BCS: "Pet parents can learn to check their cat's Body Condition Scoring, and we recommend every pet owner do so once a month," Churchill says.
• Slowing their eating: Cat feeders with puzzles or games encourage your cat's natural playfulness and curiosity, which can slow down their eating and lower their risk of obesity.
• Measuring their kibble intake: Using a weight scale to measure food rather than a measuring cup helps you avoid overfeeding your pet — or underfeeding them when cutting back on dry food.
• Swapping their food: Dry food is typically more calorie-dense than wet. Ask your vet about adding canned wet food to their diet, or swapping your dry food for a healthier kibble.

Important: Call a vet right away if your cat doesn't want to eat or drink, or begins to lose weight rapidly. This can suggest anything from environmental stress to a number of health concerns — some of which may be life-threatening. Keep in mind, too, that going without food for just a few days can make your cat very sick.

Insider's takeaway

There's more to weight loss or weight gain than switching or limiting your cat's food, which might do more harm than good without guidance from a vet.

If your cat seems a little heftier than usual, a good first step involves doing a weight check with your veterinarian.

Your vet can recommend treatment for any underlying health issues, like arthritis or diabetes, and develop the purrfect (pun intended) health plan for your kitty to bring them to a healthy weight.