# Cat Losing Muscle Mass and Weight: Causes to Check A cat losing muscle mass is losing more than fat, and the change usually points to an underlying condition instead of simple aging. Muscle wasting along the spine, hips, and back legs is one of the most common early clues of chronic kidney disease, hyperthyroidism, diabetes, or cancer in older cats. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## Quick Answer - Muscle loss looks like a bony spine, sunken hips, and thinner back legs, even if your cat's belly looks round or normal. - The most common causes in older cats are chronic kidney disease, hyperthyroidism, diabetes, cancer, and age-related muscle loss (sarcopenia). - Weigh your cat monthly on a baby scale and run your hands along the spine and hips every few weeks to catch changes early. - Sudden or rapid weight loss, weakness, vomiting, or not eating are reasons to see a veterinarian right away. - Muscle loss cannot be reversed by feeding more food alone. The underlying cause has to be found and treated. ## What Muscle Loss Looks Like and What Is Normal Muscle loss in cats is different from fat loss. A cat can lose muscle while keeping or even gaining body fat, a pattern called sarcopenic obesity [1]. That is why a cat who still looks plump can be losing strength at the same time. Run your hands along your cat's body. On a healthy cat, the spine feels like a rounded ridge under a soft layer of muscle. The hip bones are felt but not sharp. The muscles along the back and thighs feel firm and full. When a cat is losing muscle mass on the back and in the back legs, the spine becomes a hard, knobby ridge. The hip bones stick out. The thighs look flat or hollow instead of rounded. Your cat may also seem unsteady jumping onto a counter or may hesitate before jumping at all. Some muscle change is expected with age. Sarcopenia is the medical term for age-related muscle loss, and it is common in older mammals, including cats [1]. It contributes to frailty, which affects quality of life and predicts survival time [1]. Normal aging muscle loss is slow and gradual. Rapid loss, or loss in a cat under 8 years old, is not normal aging. Weight loss and muscle loss often happen together, but they are not the same thing. If your cat is dropping pounds without a clear reason, see [Why Is My Cat Losing Weight?](/knowledge/veterinary-medicine/symptom-guides/why-is-my-cat-losing-weight) for a broader look at the possible causes. ## Main Causes of a Cat Losing Muscle Mass | Cause | Typical clues | How urgent | |---|---|---| | Chronic kidney disease | Increased thirst and urination, dilute urine, weight loss, poor appetite, vomiting | See a vet within days | | Hyperthyroidism | Ravenous appetite with weight loss, hyperactivity, vomiting, a scruffy coat | See a vet within days | | Diabetes mellitus | Heavy drinking and urination, big appetite, weight loss, weakness in the back legs | See a vet within days | | Cancer and cancer cachexia | Progressive weight and muscle loss, poor appetite, lethargy, a mass or swelling | See a vet promptly | | Age-related sarcopenia | Slow muscle loss in a cat over 10 with no other signs | Routine visit | | Muscle disease (myopathy) | Weakness, pain, stiffness, reluctance to move | See a vet promptly | ### Chronic Kidney Disease CKD is one of the most common reasons older cats lose weight and muscle. In a study of senior cats whose owners believed they were healthy, 61.3% had previously unrecognized chronic kidney disease on testing [2]. That means many cats are losing muscle before anyone realizes their kidneys are struggling. One early warning sign is poorly concentrated urine. In a large study of apparently healthy mature cats, dilute urine was linked to a higher risk of later developing CKD [3]. If your cat is drinking more, urinating more, and losing weight, ask your veterinarian to check kidney values and urine concentration. ### Hyperthyroidism An overactive thyroid speeds up metabolism. Cats with hyperthyroidism often eat well or even beg for food constantly, yet they lose weight and muscle. The muscle loss is often most obvious along the spine. This condition is treatable, and catching it early protects the heart and kidneys too. ### Diabetes Mellitus Diabetes causes the body to burn fat and muscle for energy because glucose cannot get into the cells properly. Cats with diabetes often drink and urinate heavily, eat a lot, and still lose weight. Some develop weakness in the back legs from nerve damage. This is a medical emergency if your cat stops eating or becomes very lethargic. ### Cancer and Cachexia Cancer cachexia is a metabolic disease that depletes muscle tissue and is linked to about 20% of cancer-related deaths [4]. It is not simply a matter of the cat eating less. The cancer changes how the body uses protein and energy. If your cat is losing muscle quickly and seems tired or has a poor appetite, cancer needs to be on the list of possibilities. ### Age-Related Muscle Loss Sarcopenia is the slow loss of muscle that comes with age [1]. It is not a disease you can cure, but you can slow it. Muscle condition scoring by your veterinarian can catch it early and guide treatment [1]. A frailty score that includes activity level may also help predict which cats are at higher risk [1]. ### Muscle Disorders Myopathies are diseases that damage muscle tissue. They can be present at birth or develop from nutritional imbalances, injury, poisoning, cancer, metabolic problems, or inflammation [5]. One example is yellow fat disease, which causes inflammation of fatty tissue and is linked to diets high in fish or fish byproducts combined with low vitamin E [5]. Affected cats are often young, obese, and become lethargic with a tender back or abdomen [5]. This is uncommon but worth knowing if your cat eats a lot of fish. ## Red Flags That Mean Emergency Care Call an emergency clinic now if your cat: - Cannot stand or collapses - Is having trouble breathing - Has a seizure or sudden weakness on one side - Is straining to urinate or cannot urinate - Has a distended, painful belly - Is bleeding heavily or has pale gums Call your veterinarian the same day if your cat: - Has lost a lot of weight quickly, especially over days to weeks - Has stopped eating or drinking - Is vomiting repeatedly or has diarrhea - Is drooling, has bad breath, or has trouble swallowing - Seems painful when you touch the back or abdomen ## Safe Things You Can Do at Home While Waiting You cannot diagnose the cause at home, but you can gather useful information and keep your cat comfortable. - Weigh your cat weekly on a baby scale and write down the number. A 5% loss in body weight is meaningful and was the threshold used in a clinical trial of cats with kidney disease and unintended weight loss [6]. - Do a hands-on muscle check every two weeks. Feel the spine, hips, and thighs and note any new bony edges. - Track food and water intake. Measure how much your cat eats and drinks in 24 hours. - Keep a symptom log. Note vomiting, urination changes, appetite, energy, and any limping. - Offer warm, smelly food. Gently warming wet food can make it more appealing to a cat with a poor appetite. - Do not give human supplements or medications. Some are toxic to cats, and dosing depends on your cat's weight and health. - Reduce jumping demands. Put steps or ramps to favorite spots so a weak cat does not have to leap. If your cat is gaining weight while losing muscle, that is a different pattern. See [Cat Weight Gain Causes](/knowledge/veterinary-medicine/nutrition/cat-weight-gain-causes) for help sorting out what that might mean. ## What Your Veterinarian Will Check and Test Your veterinarian will start with a full physical exam, including a muscle condition score and a body condition score. These are two different scales. Body condition measures fat. Muscle condition measures muscle. A cat can score well on one and poorly on the other. Expect blood work and a urine test. A complete blood count and chemistry panel check kidney values, liver values, blood sugar, and thyroid hormone. A urinalysis checks urine concentration and looks for infection or crystals. Your veterinarian may also check blood pressure, because hypertension is common in older cats and was found in a large share of senior cats in one study [2]. If those tests do not explain the problem, your veterinarian may recommend imaging such as X-rays or an ultrasound. In some cases, an ultrasound of the epaxial muscles (the muscles along the spine) can help assess muscle loss [1]. A muscle biopsy is occasionally needed for suspected myopathy [5]. Treatment depends on the cause. For CKD, management focuses on diet, hydration, blood pressure control, and sometimes appetite stimulants. A medication called capromorelin was shown in a randomized, masked, placebo-controlled trial to promote weight gain in cats with CKD and unintended weight loss [6]. In that study, cats receiving capromorelin gained an average of 5.18% body weight over 55 days, while cats on placebo lost an average of 1.65% [6]. Your veterinarian will decide whether a medication like this is appropriate and will calculate the dose from your cat's weight and health. For hyperthyroidism, treatment options include medication, a special diet, surgery, or radioactive iodine. For diabetes, insulin and diet changes are the mainstays. For cancer, the plan depends on the type and stage. ## Slowing Muscle Loss and Monitoring at Home You cannot stop all muscle loss, but you can slow it and catch problems earlier. - Feed a high-protein diet if your veterinarian approves it. Older cats need more protein, not less, unless kidney disease requires adjustments. - Keep your cat active. Short play sessions with a wand toy or food puzzle help maintain muscle. - Treat pain. Arthritis is common in senior cats and makes them move less, which speeds muscle loss. In one study of senior cats, 77.8% had orthopedic disease on exam [2]. - Schedule twice-yearly vet visits for cats over 10. Senior cats often have abnormalities before owners notice anything wrong [2]. - Ask about muscle condition scoring at every visit so you can track changes over time [1]. - Watch for early kidney signs. Dilute urine in a mature cat is a reason to check kidney values sooner [3]. If your cat is losing weight and you are not sure whether it is normal aging, [How to Tell If Your Cat's Weight Loss Is Normal Aging or a Health Problem](/knowledge/veterinary-medicine/senior-and-chronic-care/cat-weight-loss-normal-aging-or-health-problem) walks through the differences. For cats who need to gain weight back, [Weight Loss For Cats](/knowledge/veterinary-medicine/nutrition/weight-loss-for-cats) covers nutrition strategies. ## Limitations and When to Contact a Veterinarian This article cannot tell you what is causing your cat's muscle loss. Only a veterinarian who examines your cat and runs tests can do that. Individual cases need a veterinarian, and the timing matters. Contact an emergency clinic now if your cat cannot stand, is struggling to breathe, cannot urinate, or collapses. Contact your veterinarian the same day if your cat has lost weight rapidly, has stopped eating, is vomiting repeatedly, or seems painful when touched. Schedule a routine visit within a week or two if your cat is slowly losing muscle, eating and drinking normally, and acting like themselves. Even slow loss deserves a checkup, because early diagnosis of kidney disease, hyperthyroidism, or diabetes makes treatment easier and more effective. ## Frequently Asked Questions ### Why is my cat losing muscle in the back legs? Muscle loss in the back legs often reflects a whole-body problem like kidney disease, diabetes, or cancer, or it can be age-related sarcopenia. Diabetes can also cause a specific nerve weakness in the back legs. A veterinarian can tell the difference with an exam and blood work. ### Can a cat regain lost muscle? Yes, some muscle can be regained if the underlying cause is treated and your cat eats enough protein and stays active. Age-related muscle loss is harder to reverse, but it can be slowed. A medication called capromorelin helped cats with kidney disease gain weight in a clinical trial [6]. ### Is muscle loss in older cats always a sign of disease? No, some muscle loss is a normal part of aging and is called sarcopenia [1]. The key difference is speed. Slow loss over years in a cat over 10 is more likely aging. Fast loss, or loss in a younger cat, points to disease. ### How can I tell if my cat is losing muscle or just fat? Feel your cat's spine and hips. If the bones feel sharp and the muscles along the back and thighs feel flat, that is muscle loss. If your cat feels bony all over with no fat layer, that is fat loss. Many cats lose both at the same time. ### What should I feed a cat who is losing muscle? Ask your veterinarian first, because the right diet depends on the cause. Cats with kidney disease may need a prescription diet, while cats with cancer or diabetes have different needs. In general, older cats do better with more protein, not less, unless your vet advises otherwise. ## Related Articles - [Why Is My Cat Losing Weight?](/knowledge/veterinary-medicine/symptom-guides/why-is-my-cat-losing-weight) - [Cat Weight Gain Causes](/knowledge/veterinary-medicine/nutrition/cat-weight-gain-causes) - [Weight Loss For Cats](/knowledge/veterinary-medicine/nutrition/weight-loss-for-cats) - [Why Is My Cat Gaining Weight?](/knowledge/veterinary-medicine/nutrition/why-is-my-cat-gaining-weight) - [How to Tell If Your Cat's Weight Loss Is Normal Aging or a Health Problem](/knowledge/veterinary-medicine/senior-and-chronic-care/cat-weight-loss-normal-aging-or-health-problem) - [Weight Loss Diet for Cats: Protein-Sparing Deficit and Monitoring](/knowledge/veterinary-medicine/nutrition/weight-loss-diet-for-cats-protein-sparing-deficit-and-monitoring) - [Cat Not Gaining Weight or Losing Weight: Causes](/knowledge/veterinary-medicine/digestive-and-urinary-care/cat-not-gaining-weight) - [Cat Losing Weight With Diarrhea: Causes and When to Act](/knowledge/veterinary-medicine/digestive-and-urinary-care/cat-weight-loss-diarrhea) - [Cat Loss of Appetite: Causes and When to See a Vet](/knowledge/veterinary-medicine/digestive-and-urinary-care/cat-loss-of-appetite-causes) ## References 1. [Sarcopenia, cachexia and frailty in older cats: Mechanisms, assessment and therapeutic considerations](https://pubmed.ncbi.nlm.nih.gov/42505041/). Journal of feline medicine and surgery, 2026. 2. [Clinically important abnormalities are common in senior cats perceived to be healthy by owners](https://pubmed.ncbi.nlm.nih.gov/42526494/). Journal of the American Veterinary Medical Association, 2026. 3. [Poorly concentrated urine is associated with an increased risk of developing chronic kidney disease in apparently healthy cats](https://pubmed.ncbi.nlm.nih.gov/42648349/). Journal of the American Veterinary Medical Association, 2026. 4. [β-carotene attenuates muscle wasting in cancer cachexia by regulating myogenesis and muscle atrophy](https://pubmed.ncbi.nlm.nih.gov/37975253/). Oncology reports, 2024. 5. [Muscle Disorders in Cats - Cat Owners](https://www.merckvetmanual.com/cat-owners/bone-joint-and-muscle-disorders-of-cats/muscle-disorders-in-cats). Merck Veterinary Manual. 6. [Capromorelin promotes weight gain in cats with unintended weight loss: a randomized, masked, placebo-controlled clinical trial](https://pubmed.ncbi.nlm.nih.gov/41204815/). Journal of feline medicine and surgery, 2025. ## Further Reading - [Merck Veterinary Manual: Cat Owners](https://www.merckvetmanual.com/cat-owners) - [Cornell Feline Health Center: Health Information](https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information) - [American Veterinary Medical Association: Pet Care](https://www.avma.org/resources-tools/pet-owners/petcare)