Why do cats lose weight?
When a cat starts losing weight, it usually means something has changed either in how much they’re eating or in how their body is using food. Sometimes the change is straightforward, like a decrease in appetite. Other times, weight loss is linked to an underlying health condition that affects digestion, metabolism, or overall energy needs.
Because many medical conditions can show up this way, it’s important not to brush off changes in your cat’s weight. Being underweight can make it harder—especially for older cats—to stay strong and feel their best. Finding the cause early allows your veterinarian to recommend care, including treatment and diet changes, that can help support your cat’s health over time.
What are some signs your cat might be losing weight?
Changes in a cat’s weight can be easy to miss, especially when they happen slowly. When you look at your cat every day, small shifts in their appearance can blend into the background.
Here are a few signs that may suggest that your cat’s body is changing:
- Thinner face: You might notice your cat’s facial expressions look different if they’ve lost fat around their cheekbones or eyes.
- Protruding bones: When cats lose muscle or fat, you might be able to feel their spine, hips, or ribs more easily.
- Feeling lighter: When you pick your cat up, they may feel lighter or less solid in your arms.
- Lower energy: Some cats become less active or seem more tired as their bodies lose muscle or fat.
If your cat has a thick coat or doesn’t like to be cuddled or held, these kinds of gradual changes can be harder to spot. Regular visits to your vet’s office for official weigh-ins and exams are one of the most reliable ways to track changes and catch concerns early.
How can I track my cat’s weight at home?
Although your vet will weigh your cat at each visit, it’s important to monitor your cat’s weight at home so you can detect changes as soon as possible. You can weigh your cat on a baby scale, or step on your scale while holding your cat, then weigh yourself and subtract your weight.
You can also watch for changes in your cat’s appearance using a body condition scale. This method involves assigning a number to your cat’s body condition so you can monitor their weight over time, even if you don’t have a scale at home. You should also look for changes in how much your cat eats at each meal.
If you notice a gradual change in your cat’s weight, call your vet to get an appointment on the books.
Common causes of weight loss in cats
Cats can lose weight for a variety of different reasons. Below are some of the most common causes for this kind of change.
Not eating enough food
This is one of the most straightforward causes of weight loss in cats. That said, what’s often less clear is why a cat’s appetite has changed to begin with.
Here are some of the most common reasons why a cat may not be eating enough:
- Pain: If your cat is in pain—either in their mouth or somewhere else—they may eat less.
- Competition: Other cats—or a sneaky dog—may be blocking your cat’s access to their food bowl.
- Mobility issues: If your cat’s food bowl is placed in an area that they have trouble reaching—like an elevated surface such as a counter or platform—they may end up eating less than they need.
- Pickiness: If your cat doesn’t like the type or brand of food being served, they may refuse to eat.
- Stress or anxiety: Some cats eat less when they’re stressed or anxious, such as after a move to a new home or when a new pet or person gets introduced into their lives.
Sometimes a cat will continue to eat the same amount of food but still lose weight. In these cases, their body may be using more energy than usual or their body isn't absorbing nutrients as it should. This is often because of an underlying health issue. In the sections below, we’ll walk through some of the more common conditions that can affect how a cat’s body uses food.
Stomach and intestinal problems (GI disease)
Gastrointestinal (GI) diseases can make it harder for cats to digest food or absorb nutrients, which can cause weight loss.
Examples of common GI conditions in cats include:
- Intestinal parasites
- Inflammatory bowel disease
- Pancreatitis
If your cat has GI disease, you may notice other signs as well, such as decreased appetite, vomiting, or diarrhea.
Diabetes in cats
Diabetes is a common condition in middle-aged and older cats. Cats with diabetes often feel very hungry but still lose weight. Their bodies can't use food the way they should, so their food doesn’t give them the energy they need.
Hyperthyroidism
Many older cats get hyperthyroidism. This happens when the thyroid glands make too much thyroid hormone, which causes the body to work faster and burn calories more quickly. Cats may lose weight and act very hungry, even when they eat the same amount of food (or more).
Kidney disease
Many older cats develop chronic kidney disease, which means the kidneys are less able to filter waste. This can lead to signs like eating less and losing weight.
Tumors
Some tumors—whether noncancerous or cancerous—can cause weight loss. Tumors in the stomach, intestines, or other places in the body may make cats feel sick or not want to eat. Other tumors use up the body's calories, so your cat gets less nutrition.
Common patterns of weight loss
Sometimes, the pattern of a cat’s weight loss can give you and your vet clues about what might be going on. While every cat is different, there are some common patterns to be aware of:
- Gradual weight loss: Cats may lose weight slowly over the course of months—or even years. This can happen when cats don’t eat enough or have a condition that gets worse over time.
- Sudden weight loss: Cats may lose a noticeable amount of weight over a short period of time. This is most common when cats have a serious illness that develops or worsens quickly.
- Muscle loss: Some cats lose muscle on either side of the spine or around the hips or legs.
- Fat loss: Cats may lose fat before losing muscle, depending on what’s causing their weight loss.
When weight loss happens suddenly
Sudden weight loss could mean that your cat has a serious health condition. If your cat’s weight changes quickly—but they’re otherwise feeling well—see your vet as soon as possible.
Overweight cats who suddenly lose a lot of weight—most often from not eating, but also from illness—can develop a condition called hepatic lipidosis, also known as “fatty liver.” This condition can make a sick cat even sicker and may even be life-threatening. If you notice that your cat isn’t eating as much, they’re losing weight rapidly, and/or they aren’t acting like themselves, visit an emergency veterinary practice right away.
Don’t forget: Cats are very good at hiding things when they aren’t feeling well. Sudden weight loss—whether your cat seems sick or fine—is something that needs to be checked out by your vet. They’ll be able to help you figure out what’s going on—and, more importantly, come up with a plan for what to do next.
How do vets figure out what’s causing weight loss?
Veterinarians use a series of tests to help identify the cause of a cat's weight loss. These may include:
- A physical exam to check all body systems
- Blood work to check organ function and thyroid levels
- Urine testing to check kidney function and for signs of infection
- X-rays or an ultrasound to look for changes in organ appearance
These tests often help explain what’s going on. If they don’t provide clear answers, your vet may refer your cat to an internal medicine specialist.
Final thoughts
Although weight loss is more common as cats get older, there’s still a lot pet parents can do to help catch changes early and support their cat’s health. Regularly feeling your cat’s body, keeping track of their weight, and staying up to date on routine veterinary care puts you in the driver’s seat. This kind of proactive care can make all the difference for your cat’s health in the long run.
Frequently asked questions
Frequently asked questions about this topic
A healthy weight depends on your cat’s body size, age, and lifestyle. In a cat with a healthy body condition, you should be able to feel the ribs and see a “waist” when looking at them from above. Most cats also have a pouch of loose skin that hangs from their lower belly. If you can easily feel or see your cat’s ribs, spine, or hip bones, they may be underweight.
Yes, small weight changes over a cat’s life can be normal. Losing a few ounces here and there isn’t necessarily concerning unless it becomes a pattern. If you notice that your cat continues to lose weight, check with your vet right away to help figure out why and what to do next.
The short answer is no. You shouldn’t make any changes to your cat’s diet without checking with your vet first. If your cat needs to gain weight, your vet may recommend a prescription diet food that has more calories and nutrients. It’s important to understand why your cat is losing weight before making any diet changes, so make sure your vet’s in the loop every step of the way.
Yes. Some health conditions that lead to weight loss don’t cause other obvious changes right away. Many cats still eat, play, and act like themselves at first. As their disease progresses, you may notice changes in their appetite or other signs. If your cat is losing weight but still seems happy, make an appointment with your vet to figure out what else might be going on.
