Why Is My Senior Cat Losing Weight? Causes and What to Watch

A senior cat losing weight is one of the changes I would never wave away, because it is so often the first outward sign that something is wrong, and sometimes the only one. If you are wondering why your senior cat is getting skinny, the change usually comes on slowly, a little less cat under your hand each month, until one day you pick her up and feel the ridge of her spine where there used to be padding. By then a good deal can be gone. The single most useful thing you can do is notice it early, and the single most useful question to ask is whether she is losing weight while eating well, or while eating less. The two point in different directions.

This page maps the senior cat weight loss causes and what to do about them. It is not a diagnosis for your particular cat. Steady weight loss in an old cat is a reason to see your vet, because most of the causes are things they can treat, and treat better the earlier they are caught.

How worried should I be about a senior cat losing weight?

Worried enough to have it checked, but not to panic. Weight loss is rarely nothing in an older cat. VCA describes it as something that can be due to simple problems of feeding and nutrition or can be due to a variety of medical conditions that result in poor digestion, decreased absorption of nutrients, or loss of nutrients from the body. Most of those medical conditions are common in old age and very much worth catching.

At the same time, a slow drift down in an aging cat is not always disease. VCA notes that a cat's body condition and weight naturally decline with advanced age. So the thing to weigh is not any single reading but the trend and the pace: a cat coming off her weight steadily, or quickly, or alongside any other change, has earned a vet visit. Old age is a reason to look harder for a cause, not a reason to assume there isn't one.

Losing weight but eating well: the pattern to know

This is the combination that surprises people, and the one most worth recognizing. A cat can shrink while eating the same amount or more, and when she does, a short list of conditions is usually behind it.

The classic is an overactive thyroid. VCA puts it plainly: the most common clinical sign of hyperthyroidism is weight loss due to the increased metabolism despite an increased appetite. The gland runs the body's engine too fast, so she burns calories quicker than she can eat them. A cat who is suddenly ravenous, restless, and getting bony at the same time fits hyperthyroidism until proven otherwise.

Two others belong here. Diabetes can cause weight loss alongside a big appetite and heavy drinking, because the body cannot use the sugar it is taking in. And problems in the gut, where food goes in but the goodness does not get absorbed, do the same: this is the poor digestion, decreased absorption of nutrients VCA describes, and it covers inflammatory bowel disease and, less kindly, intestinal cancer. If she is emptying her bowl and still fading, that is not reassurance. It is a reason to move a little faster.

Losing weight and eating less

When appetite drops off along with the weight, the field is wider, because almost any illness that makes a cat feel unwell will also put her off her food. VCA is direct that a decreased or absent appetite can signal an underlying medical problem.

A few causes come up again and again in old cats. A sore mouth is high on the list, and easy to miss: a cat with dental disease may approach her food eagerly, then back away because chewing hurts. Kidney disease brings nausea that dulls appetite as it advances. Cancer can take both weight and appetite. And a cat who has simply stopped eating for any reason is an urgent matter in her own right, because cats who go off their food for a couple of days can develop a dangerous liver problem on top of whatever started it.

The quiet muscle loss of aging

There is a version of this that the scale can hide. An old cat can hold a fairly steady weight and still be trading muscle for less useful padding, so she feels bonier over the spine and shoulders even as the number holds. The answer is not to feed less. VCA notes that dietary protein is a critical nutrient for maintaining good physical health in the face of aging, and notes that some older senior cats may need an increase in their caloric and protein intake to sustain a normal physique as their body condition and weight naturally decline with advanced age. An aging cat generally needs plenty of good protein, not a thinned-down diet, and there is more on that in feeding a senior cat. It is also worth checking what she is already on, since some formulas sold for older cats are lower in protein than the adult food beside them and nothing obliges a "senior" bag to be anything in particular. Our calorie calculator gives you a starting daily target if you want a number to feed toward rather than a guess. If she is also stiff or slow to jump, losing muscle and losing mobility tend to feed each other. The fuller picture, including how to feel for it and how to tell age from illness, is in muscle wasting in cats.

How do I tell if she is actually losing weight?

Trust the scale over your eye, because your eye sees her every day and adjusts. The simplest home method is to weigh yourself, then weigh yourself holding her, and take the difference. A kitchen or baby scale works for a lighter cat. VCA suggests you schedule periodic weigh-ins at home or at your veterinarian's clinic to monitor any weight gain or loss. A monthly weight, jotted somewhere, will show you a trend long before it is obvious.

Between weigh-ins, use your hands. Run them gently along her spine and over her ribs and hips. You are feeling for bones that are becoming easier to find than they were. And remember the arithmetic works against a small animal: half a pound off a ten-pound cat is five percent of her, the same share as a one-hundred-and-eighty-pound person dropping nine pounds without trying. What looks like a rounding error on the scale is a real loss on a cat.

What the vet will check

Because so many causes overlap, vets start broad. VCA's baseline workup for a cat losing weight is a complete blood count (CBC), serum biochemistry profile, urinalysis, parasite testing, and evaluation of thyroid hormones, which between them screen for the kidney, liver, thyroid, diabetes, and infection causes at once. Blood pressure and a proper look in the mouth usually come with it, and depending on what turns up, imaging or a closer look at the gut may follow. It is worth raising weight at her regular senior check-up even when nothing else seems wrong, since a recorded trend is exactly what makes an early diagnosis possible.

Frequently asked questions

Is it normal for senior cats to lose weight? A gentle decline in body condition can be part of aging, and VCA notes that weight naturally declines with advanced age. But noticeable or ongoing weight loss deserves more than a shrug toward old age. It commonly has a specific, treatable cause, and it deserves a vet's look.

Why is my old cat losing weight but still eating? The classic reason is an overactive thyroid: VCA calls weight loss despite an increased appetite the most common sign of hyperthyroidism. Diabetes and gut conditions that stop her absorbing her food can do the same. Eating well does not rule out illness, and in these cases it is part of the picture.

How much weight loss should worry me in a cat? Any steady, unexplained loss is worth a call, because a cat is small enough that a little is proportionally a lot. There is no need to reach a particular number before acting: a clear downward trend over a few weeks, or loss paired with any other change, is reason enough.

Can old age by itself make a cat lose weight? Muscle loss with age is real, and protein helps hold it off. But age alone is a diagnosis your vet reaches only after ruling the treatable causes out, not one to assume at home. Check for a cause first.

When to call the vet

Book a visit for any clear, ongoing weight loss, and sooner if it comes with increased thirst, a change in appetite in either direction, vomiting, or low energy. Go the same day if she has stopped eating altogether for a day or more, which is its own emergency in a cat. If she is also drinking and urinating more heavily, that particular trio has its own short list of causes, covered in drinking more and losing weight.

Biscuit lives on a kitchen scale, more or less. I weigh her the first of every month, holding her against my chest on the bathroom scale and doing the subtraction, and I write the number on the same scrap of paper I have used for two years. It is not precise to the ounce, and it does not need to be. A senior cat losing weight shows it on the scale long before it shows on the body. What weighing gives me is the shape of the line, and the shape of the line is what tells me, long before her spine does, when it is time to make a call.

Sources

• VCA Animal Hospitals, Testing for Weight Loss in Cats
• VCA Animal Hospitals, Hyperthyroidism in Cats
• VCA Animal Hospitals, Feeding Mature, Senior, and Geriatric Cats