Weight Loss in Cats: Causes & What to Do

When it comes to cat weight concerns, most of the conversation focuses on cats being too heavy. And with good reason: around 60% of cats are overweight or obese. But weight issues aren’t just about excess pounds. Your cat can also be underweight, and unintentional weight loss can be just as concerning as obesity.

Even if your cat starts out overweight, losing too much weight can signal a serious health problem. A sudden loss of more than 5% of body weight or a gradual loss exceeding 10% is a red flag, this would be like a 60 kg person suddenly losing 5 kg. Often, these changes can precede visible signs of illness by weeks or even months, making early detection crucial.

Worried that your cat may be underweight or losing too much weight? Keep reading to learn what could be behind your cat’s weight loss, why it matters and when to seek help.

Even if your cat is technically overweight, a drop in weight might be a sign of something more serious. Cats are experts at hiding pain or discomfort, so changes that might seem subtle to us can actually signal illness.

The first step is knowing your cat’s normal weight. Regular weigh-ins, using tools like our Body Condition Score (BCS) chart, can help you spot meaningful changes. For even more precision, Muscle Condition Scoring (MCS) can detect muscle loss, which often occurs even in cats with normal or high body fat. Together, these assessments give a more complete picture of your cat’s health.

Not all weight loss is equally concerning, so context matters. For example, a 6kg cat losing 200 g in a month (around 3% of body weight) is generally not alarming. But a 3kg cat losing the same 200 g (nearly 7% of body weight) is clinically significant and warrants veterinary attention. Because cats are small, even seemingly minor changes on the scale can reflect meaningful health shifts.

If your cat is losing weight without a clear reason, whether gradually or suddenly, don’t assume it’s a positive change, even in previously overweight cats. Unexplained weight loss often precedes other visible clinical signs and can impact lifespan. Some smart litter boxes can even track weight automatically, making it easier to detect changes early.

When in doubt, take your cat to the vet.

Sudden weight loss might be caused by:

• Chronic enteropathies — linked to food intolerance/allergy, or inflammatory bowel disease — and pancreatitis

• In senior cats, endocrinopathies — such as hyperthyroidism and diabetes — chronic kidney disease, dental disease and arthritis are common

• Infectious diseases, including viral and parasitic, especially in young kittens and/or cats with conditions associated with immunosuppression

• Oral pain

• Cardiorespiratory disease (including chronic snufflers and heart failure)

• Neoplasia or cancer

• Environmental stressors and anxiety. 

If your cat is losing weight, there are a few things to troubleshoot, but a behavioural diagnosis must exclude medical conditions.

If you spot your cat getting skinnier and there’s no sign of any sickness or pain, take a look at their food bowl. They might be eating less than you think.

Do you have other pets? Another cat or dog might be finishing their dinner for them. Or chasing them away from their bowl. You may want to think about feeding your cat in another room, away from other pets to make sure they can eat their fill and put weight back on. 

Other pets not a problem? Check out the back of their food packet. If you’ve recently changed food brands, there might be fewer calories. And your cat might not be getting what they need to maintain their weight. 

Is their diet complete and balanced? Not all are (especially wet food), so double check the label reads ‘complete’ and not ‘complementary’.

Make sure your cat’s food bowl is in an easily accessible spot — they may be less willing to jump onto a counter or high surface to eat. Keeping the bowl elevated to shoulder height will also decrease the pressure on the elbows when bending to eat or drink. 

If your cat is showing signs like itchy skin, thinning fur or an unsettled stomach, it could be a reaction to something in their diet — but these symptoms can also indicate other underlying issues. That’s why it’s important to speak to your vet for advice before making changes.

Nutritional imbalances, poor digestibility or food sensitivities can all affect your cat’s health and comfort. Feeding a complete and balanced diet that’s highly digestible can support better nutrient absorption, healthy skin and coat condition — which is where KatKin comes in.

KatKin is fresh, vet-formulated cat food made without unnecessary fillers or artificial additives. It’s specially formulated to provide key nutrients like taurine, choline, Vitamin B12 and fatty acids in their natural, bioavailable forms. These are the building blocks for coat health, skin integrity and muscle mass. And our simple, transparent ingredient lists make it easier for you and your vet to identify what works best for your cat.

If you think your cat is underweight, the first step is always a vet check to rule out any underlying health issues. If your cat gets a clean bill of health, it's worth having a conversation with your vet about their individual nutritional needs.

Some cats naturally have higher energy requirements, and not all calories are absorbed equally — diet format, ingredient quality and digestibility can all impact how well your cat utilises what they eat. A highly digestible, complete and balanced diet like KatKin can support healthy weight gain by helping your cat make the most of every bite.

• Healthy (but skinny) cats may simply need more calories a day. This could look like an extra meal. Or a midnight snack. KatKin is formulated with your cat’s ideal weight in mind. So if you already feed them our delicious recipes, they’re already getting all the calories they need. 

• If you have multiple cats, one might be stopping the other from eating. Separate your skinny cat from the greedy one at dinner time. Pop them in another room and allow them to eat their meal in peace.Nervous or anxious cats will be more willing to chow down in a calm, quiet space. Away from noise, appliances, children, and other pets. 

• If you feed your cat dry kibble, offer them something extra tasty as well. Canned food, KatKin fresh cat food, or toppers like cooked, shredded chicken or flakes of tuna.

• Picky cats might be encouraged to eat more if they’re offered a variety of flavours and textures. Here at KatKin, we offer a wide range of delicious recipes in 2 different textures: smooth and chunky.

• Make their food extra tempting by popping it in the microwave for a few seconds. (Not too long. So they don’t burn their mouths.) When their food is warmed up, it smells much more appetising. We’d all rather eat a hot roast dinner rather than one that’s gone cold, wouldn’t we?

• Try adding a small amount of  tuna juice (fresh water, not oil or brine) to their dinner. Or a spoonful of unsalted chicken broth. Or even a dusting of our Sprinkles to entice them to the bowl.

If you’ve noticed your senior cat losing weight, it’s important to speak to your vet — significant weight or muscle loss isn’t just a normal part of ageing. While mild changes can happen over time, ongoing weight loss often points to an underlying health issue.

We recommend regular health checks for senior cats at least every six months, to catch any issues early and help manage their wellbeing effectively.

That said, as cats age, their ability to digest and absorb fat and protein can decline, which means they may need a more targeted, higher-quality diet to maintain muscle mass and overall health.

KatKin is formulated with these needs in mind: fresh, high-quality protein and optimal levels of vitamins and minerals to support ageing bodies. Our gently cooked meals are highly digestible, with no artificial additives or long shelf lives — and we tailor portions based on your cat’s weight, lifestyle and life stage, to help them stay strong and healthy.

Cats are very sensitive to stress, and it can affect them more than we often realise. Stress is a common cause of reduced appetite, which can lead to weight loss if your cat isn’t eating enough over time.

Common stressors include children, new pets, moving house and construction work — but cats can also be stressed by things we might not immediately recognise, like changes in routine, loud noises, unfamiliar visitors or even subtle shifts in their environment like redecorating the living room or rearranging furniture.

Try to identify and minimise these stressors wherever possible. Feeding your cat in a quiet, private space can help them feel safe and calm. If stress continues to be a problem, consulting a feline behaviourist can be invaluable in optimising your cat’s environment and resources, ensuring their needs are truly met.

If your cat is both losing weight and showing signs of hair loss, it’s important to take them to the vet — as this combination often points to an underlying medical issue that needs attention, which could include:

• Parasitic infestations, such as fleas (a common cause of intense itching and overgrooming) and worms (which can contribute to weight loss, especially in younger or outdoor cats).

• Pain-related overgrooming — from joint pain, abdominal discomfort, or even neuropathic pain, cats may excessively lick or chew at certain areas, leading to hair loss.

• Allergies can sometimes cause both hair loss and weight loss, though rarely both at the same time. Whether it’s food, something in the environment, a flea bite reaction or an overlap of sensitivities.

• Nutritional deficiencies, particularly if the diet is incomplete or poorly absorbed, can contribute to coat thinning and gradual weight loss.

• Cutaneous lymphoma or other cancers, while rare, can affect the skin and internal organs, causing both visible skin changes and weight loss.

• Fungal skin infections, such as ringworm (despite its name, it’s not a worm but a fungus) — typically causes circular patches of hair loss, sometimes mistaken for behavioural overgrooming. It’s more common in kittens, far less of a concern in healthy adult cats, and shouldn’t cause weight loss.

• Endocrine disorders, like rare adrenal gland diseases (e.g. hyperadrenocorticism), which may lead to symmetrical hair loss and muscle wasting.

When stress may be a factor:

Stress, anxiety or obsessive behaviours (like overgrooming) may also play a role — but these are generally diagnoses of exclusion, meaning medical causes should be ruled out first. True behavioural overgrooming often arises when other needs (environmental or physical) aren’t being met.

You might notice that your cat is losing weight in the hindquarters. They’re usually slimmer and more muscular in this area. Which makes any weight loss here much more shocking. Weight loss can make their hips look sunken in, with the base of the spin sticking out more than normal. This is commonly due to a loss of muscle mass. And it’s a sign that something is wrong. So make sure you take them to the vet So make sure you take them to the vet and check their Muscle Condition Score.

Cats are experts at hiding when they’re not feeling well. So if your cat seems to be eating normally — or even more than usual — but is still losing weight, it doesn’t mean they’re healthy. Conditions like hyperthyroidism, diabetes, chronic enteropathy or certain cancers can cause increased appetite while your cat continues to lose weight.

Because some of these conditions can be serious or even life-threatening, it’s important not to dismiss this as normal. If you notice any rapid or unplanned weight loss, regardless of appetite, please take your cat to the vet for a thorough check-up.

If you’re worried about your cat’s weight, it’s a good idea to call your vet. It might be that they would benefit from a different diet or increased calories, but weight changes can also be a sign of an underlying medical condition. Early diagnosis helps prevent frailty, speeds recovery, and ensures your cat can continue living the best of their nine lives.

Ignoring pain, nausea or other symptoms not only delays treatment but also compromises your cat’s welfare — so when in doubt, it’s always better to be safe and get professional advice.

Underweight cats have reduced fat and protein reserves, which are essential for coping with illness, surgery or recovery. A low muscle condition score is linked to several serious health risks, including:

• Weakened immune system and increased susceptibility to infections

• Delayed wound healing

• Reduced tolerance to anesthesia

• Higher risk of complications during hospitalization

• Shortened lifespan in many chronic diseases

In senior cats, weight and muscle loss are strongly associated with greater morbidity and mortality — even when the primary illness is well-managed. This highlights the importance of addressing weight loss early to improve your cat’s quality of life and long-term health.