My Old Dog Is Losing Weight Even Though They Are Eating. What Can Cause This?


Old Dog

By Dr. Monica Tarantino

Seeing your old dog starting to lose weight unintentionally is challenging, especially if your dog spent most of its life in good condition! For some senior dogs, you may see the weight loss occur slowly over time. Yet, for others, it may happen quickly and before you even have time to intervene!

Many dog owners are concerned about weight loss in their older dogs. This blog will discuss common causes of weight loss and what to do if you see this in your older dog. We will also look at how you can ensure your dog is still healthy.

Why Is My Dog Losing Weight Even Though He Is Eating?

Dogs can lose weight for all sorts of reasons. Let’s talk about some of the most common causes of weight loss in older dogs that are still eating.

Diabetes Mellitus

One common reason for an older dog who is eating a lot to lose weight is diabetes.  Diabetic pets lose weight quickly because their bodies cannot generate sufficient insulin to help them convert their food into usable energy. 

Most diabetic dogs will also have other signs in addition to weight loss, with the most common one being increased drinking and urination.  If you pay attention to your dog’s eating and drinking, the increase in their water consumption is often very noticeable.

Diabetes Mellitus

If you suspect your dog has diabetes, please contact your vet right away. Dogs with diabetes can get sick very quickly.

Many owners with diabetic dogs will notice that they are ‘always at the water bowl’ or recall that they have to fill it up way more than expected. With diabetic dogs, they are typically Type 1, which means their pancreas is unable to produce adequate insulin to regulate glucose adequately. Dogs that are diagnosed with diabetes will need insulin supplementation for life and can get very sick without it.

Signs of diabetes in dogs may include the following symptoms:

  • weight loss
  • excessive urination
  • increased hunger
  • frequent water consumption

Cataracts may develop because of diabetes, so vision issues may also be a sign.

Cancer in Old Dogs

Cancer in Old Dogs

Cancer is the leading cause of death in older pets, and a common sign of cancer in old dogs can be weight loss and loss of muscle mass. This type of weight loss is often one of the first symptoms that many dog owners observe in their sick pets. 

As a vet- often when I see fast weight loss in older dogs, I get concerned about a cancerous process, although this is not always the case as parasites and other diseases like diabetes can certainly cause this. So, if you notice this in your pet, bring them in immediately.

Cachexia is a complex metabolic syndrome that is often associated with illnesses like cancer, heart disease, and kidney disease and can lead to weight loss.

Not all dogs with cancer will have weight loss, so keep an eye out for changes such as decreased appetite, lethargy, new bumps, diarrhea or vomiting, increased drinking and urination, and limping.

The truth is that older dogs have very few ways to ‘tell you’ that something hurts or is off. So, changes such as lethargy and withdrawn behavior should prompt you to schedule an examination for your dog with your vet. The veterinarian can perform diagnostic tests to confirm or rule out cancer; once the diagnosis has been made, treatments will be available for your pet.

Kidney Disease in Old Dogs

As dogs age, the cellular function of many of their organs and systems can begin to experience decline. Dog’s kidneys are a common place where we start to see disease. Many dogs will develop something called chronic kidney disease, which is best picked up with bloodwork and urinalysis. 

Kidney Disease in Old Dogs

Chronic kidney disease can gradually cause something called cachexia, which we discuss in more detail in the cancer section. 

In the later stages of chronic kidney disease, many dogs will start having a decreased appetite because they do not feel as good. If you notice any signs of increased drinking, urination, decreased appetite, or lethargy, that is a reason to bring your pet to the vet immediately.

It is important to note that not all dogs with kidney disease will look ‘sick’ or even show weight loss at various stages of the disease. Early in the disease, dogs often look normal and have good body condition. Something as subtle as a mild increase in thirst or urination may be the only sign you see. So, even if you notice a slight change in your dog, it’s best to have him checked out by your vet.

Because old dogs do not always show signs of kidney disease, it is even more essential to keep a close eye on their overall health with regular visits to the vet, even when they seem healthy. Performing bloodwork and a urinalysis on them annually or semi-annually is also recommended.

Heart Disease

Heart problems in dogs can quickly go undetected for a long time because sometimes there are few, even subtle, signs. Some will develop heart disease with age. 

Older dogs with more advanced lung or heart disease can certainly experience weight loss due to a process called cachexia. 

Parasites such as heartworm disease can also cause heart disease and contribute to the risk of heart failure in an older dog.  If you know your dog has a heart murmur, and you are noticing weight loss, schedule an appointment with your vet to bring it up.  

For older dogs with a heart murmur, any signs of increased breathing rate or effort, reluctance to sit down, or difficulty getting comfortable are all considered emergencies, and veterinary care should be sought out immediately. If you are wondering if that is what you are seeing, then call your vet or an emergency vet. It is always better to be cautious in these situations.

Gastrointestinal Disease

Another cause of weight loss can be gastrointestinal disease, affecting the stomach, intestines, pancreas, or colon. If your dog has any signs of vomiting or diarrhea, even if it is chronic and they seem ‘okay’ otherwise, this can be a sign of underlying gastrointestinal disease. 

Just because a dog seems ‘okay’ otherwise does not mean we should allow them to have chronic diarrhea or intermittent vomiting that goes unchecked.  Gastrointestinal disease can be serious, and signs can range from decreased appetite, regurgitation, soft stool or diarrhea, vomiting, hunching due to stomach pain, and lethargy.  

Examples of common GI diseases in older dogs with weight loss can include a lot of things such as inflammatory bowel disease parasites, cancer, and more.  Your vet may recommend starting with diagnostics such as bloodwork, ultrasound and, X-rays, a fecal.

Inadequate Calories

On occasion, inadequate calories can be a cause for weight loss. So, paying attention to what your dog eats compared to what they used to eat is essential. 

For example, some owners may switch their dogs from kibble to canned food and keep the ‘amount’ they feed the same. This may not work as often because there is a lot more water in canned food, so just gauging ‘the amount’ of dog food is the same in the bowl comparable to previous dog foods may not work.  This also applies to different bags of kibble or any dog food.  When switching brands or types of dog food, you must consider that even among the same types of dog food, calories/cup will be different.  

Keeping a food journal and calculating total daily calories is also really helpful.

If you have multiple dogs or feed them all out of one bowl, it is best to stop that practice and have a feeding system in place so you can see who is eating what and how much.  It is hard to determine if a dog is getting adequate calories or changes in calories if you have multiple dogs sharing out of a bowl that is down all day.

The same applies to when you have a new dog or puppy in the house.  Often, an older pet who is dealing with health issues is less strong or persistent than a younger animal, and so they may be getting their food eaten by the younger animal if you are not diligent and watching what is happening.  Some old dogs may eat part of their food, and the younger dog will finish it.  All of this can account for missed calories.  

Your vet can also give you a calorie count for your pet to help you determine how many calories per day your older dog, who is losing weight, should be eating.  Then, you can carefully measure this daily and see if it is adequate.

Old Dog

5 Tips to Help an Old Dog Losing Weight but Eating

It can be scary when you see your older dog starting to lose weight and muscle mass. So what do you do if you notice this?  Below, I talk about five different steps you can take to help your older dog.

Find the Cause

The first step to helping an old dog that is losing weight but eating is heading to the vet to try to find the cause. This means seeing your vet and doing diagnostics. An excellent place to start on a dog is often bloodwork, urine, and fecal, but your vet may recommend doing more like X-rays or an ultrasound, depending on their concern.  They may be able to identify diseases or illnesses that can be diagnosed during a regular check-up. 

Depending on the underlying cause, some causes of weight loss in an older dog that is still eating may be able to be cured or managed, while others may require a more serious conversation. The sooner you seek help, the sooner you can help your dog.

Do not delay seeking treatment for a dog because you are worried about a diagnosis. Understanding what happens will help you make the best decision for your dog. Some diseases may require frequent visits and follow-ups with your vet.

Keep a Food Diary

Until you can get into the vet, keep a detailed food diary writing down all the things your dog eats every day.  This includes treats and human food.  When feeding them anything, you want to measure food before you give it to them so if there is any left, you can approximate how much they ate. This will also help your vet!

Won’t eat her dog food but will eat treats? Write it down!  Also, try to gauge the appetite of your dog every day. Keep it simple with notes like normal appetite or eating 50% of the usual amount of food but eating all treats.  

Get an Estimate of the Total Daily Calories Your Pet Should Eat

You can call your vet’s office and ask them to help you estimate the amount of calories your dog should be getting to maintain their weight. You can use this to see if your pet is close to achieving this.  This number may vary depending on what type of metabolic state your pet is in, but you can still get a rough idea. My friend Nikki, who is an RVT and has a master’s in animal nutrition, has a great blog that dives a little bit more into the topic of how much food your dog should eat. 

Enhance their food

Regarding general recommendations, pay attention to the amount of food your dog is eating and the calories. Trying to enhance their food with a small amount of boiled chicken or egg whites or low sodium chicken broth can be helpful if they have a decreased appetite, but always double-check this with your vet. 

Your vet may also have other options of prescription foods that may enhance their appetite. You can also consider a small amount of wet or fresh food they may like (here’s one I like for picky dogs).  For decreased appetite, you’ll want to make sure you have identified the cause to help the pet better. Sometimes, switching up foods, supportive medications, and appetite stimulants can help.

Keep track of their weight.

Try weighing them once every two weeks (all dogs should be a proper weight that is neither too heavy nor too light). If in doubt about what exactly is going on internally, speaking with your vet about dietary changes would be a good idea before introducing new things into the diet. Two scales I like that work well at home are this one for larger dogs and this one for smaller ones.


The first step to figuring out why your old dog is losing weight is figuring out the reason why. Start with a trip to the vet to see if some diagnostics help uncover this. Dogs hide illnesses well, so even if they ‘seem okay’ on the outside, unintentional weight loss in an older dog is often a sign of something occurring under the surface.

Are you interested in learning more about senior dog health or nutrition needs? Then check out our courses and mini-courses for pet parents. 

(Affiliate links may be included in this blog, meaning we may earn small commissions should you make a purchase from our links. Thank you for supporting our small business.)


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