Dog Losing Weight: 10 Reasons & Catching It Early

Even if your furry buddy’s a bit on the trimmer side, it can be pretty alarming dealing with a dog losing weight seemingly out of nowhere. Have they been:

• Skipping meals?
• Burning off too much energy during playtime?
• Or are they suffering from a sickness, injury, or infection that might be causing weight loss in dogs?

Now before we all panic, let’s start by clearing things up. If your dog’s weight varies a bit over time, it’s 100% normal. They might’ve shed a few pounds due to completely harmless, benign reasons.

But if you’re dealing with unexplained dog weight loss, it could be a sign that something’s wrong.

So we’re going to cover all the reasons underlying weight loss in dogs – and how you can catch on to the subtle changes in behavior (like how active they are) that signal your dog might not be feeling their best. Let’s get started.

Why is my dog losing weight?

Now to address the elephant in the room (or…well, the puppy on the scale) – there are a whole bunch of reasons your dog might be losing weight. Ranging from relatively benign – even positive – reasons…to more serious, concerning ones.

(It’s similar to why dogs might suddenly stop eating – or just seem more hesitant around meals, overall.)

So let’s tackle the reasons behind weight loss in dogs, one by one. It could be because…

You’ve switched up your dog’s diet (and they’re not having it!)

If you’ve switched dog food brands or if your dog’s regular food just got reformulated, you might find them shedding some pounds. (Mostly from eating less overall.)

Because besides your new dog food being healthier, more filling, or including fewer calories – it could also be that your dog is hesitant trying out something “new”.

• Some tend to be picky eaters and don’t adapt so well to a big change, like in their diet.
• Your dog’s sense of smell alerts them to new ingredients in their meal, which they might not be familiar with.
• So they might only nibble around a new kind of food and eat smaller portions overall.

💡Your dog’s sudden food shyness makes sense from an evolutionary perspective. A wild dog or wolf might also hesitate before eating something “different” – there would be no way of telling if they’d get sick or not after, right? (Which would make them easy prey if weakened.)

All these reasons could underlie why your dog has gone from inhaling their meals to taking daintier bites over time.

So if you’re dealing with an overweight dog and want to help them adjust to a healthier diet, start slow and introduce their new food bit by bit. This will help them adapt to a change better.

Your dog’s workout routine is paying off

Now if you’re wondering – my dog is losing weight but eating normally – what gives? – we’ve got you covered.

Because another benign, positive reason for weight loss in dogs is if they’ve gotten more active lately.

Maybe you’ve been taking them on walks lately or they’ve been getting up to endless zoomies to keep themselves busy when you’re out at work.

(Or they’ve made some new playmates around your backyard – like the local squirrels – or even your neighborhood.)

Now even if your dog needed to lose those pounds anyway, it’s still smart to monitor their activity (and any weight loss). In fact, vets even recommend doing so to catch on to any health or mobility issues early on.

“Keep track of your dog’s energy levels, especially how long they are able to walk.

If you notice significant declines, it could be a sign of pain, heart disease, or other illness.”

– VCA Animal Hospitals

💡So you could either note down your dog’s everyday activity in a journal – or have actionable health data at hand with an Activity Tracker that’s built for pets (and pet parents.)

Either way, it can keep you accountable to your dog’s daily exercise routine and help your buddy live a longer, happier, healthier life by your side.

Your dog’s mental health isn’t doing so well

Besides switching up your dog’s diet, if you’ve just moved houses or are traveling with them, it might stress out your dog.

(Because much like us, a change in routine – no matter how positive – can be stressful or even anxiety-inducing for them.)

Similarly, your dog might also eat less (and end up losing weight overall) when facing stressful situations, like:

• You bringing a new pet (or baby) home
• Being made to eat next to a more aggressive pet (yes, that includes your cat too)
• Losing a loved one (not just if they pass away, but even move away for college or just aren’t around anymore)
• Recovering from a surgery
• Switching to a new medication
• You not allowing them outdoors as often (like if it’s cold outside and they’re used to frolicking around your backyard)

Much like us, dogs can – and do – experience low mental states like depression and even post-traumatic stress disorder. All of which can cause weight loss, which – thankfully – usually isn’t permanent.

Because once your dog adapts to the change, you might see them gradually cheering up with time. In these cases, their weight might vary – but also return to normal as they adjust to their new surroundings, roommate, or routine.

Your dog might be pregnant

Got an un-spayed dog at home that seems more fussy around meals lately? It’s possible they could be pregnant and are experiencing hormonal fluctuations that reduce their appetite. (Which cause them to lose weight over time.)¹

Initially, this kind of change in appetite is completely normal – because the puppies are growing quite slowly. But it shouldn’t persist or cause your dog to lose weight rapidly or suddenly.

It’s why vets recommend you:

• Check with them regarding what’s a normal pregnancy weight for your dog (based on their age and breed)
• Monitor your dog’s weight throughout their pregnancy – ideally, with a dog BMI calculator
• Get them in for a checkup the minute you notice something abnormal. (Especially within the first 1-6 weeks.)

💡Plus, one of the first signs your dog is pregnant? A drop in their overall activity – or if they just seem more tired and less active than usual.

Which you can catch on to early with regular Activity Tracking – so you can get your dog checked at a vet much before their condition progresses. (And help them deliver safely and have a healthy litter of puppies.)

Discover Activity Tracking

Your dog might be too hot or too cold

Hot or cold weather are both reasons that can affect weight loss in dogs.² Here’s how:

• Your dog might feel more lethargic or experience an appetite dip in hot weather. (So they eat less overall – and end up losing weight.)
• Your dog might burn more calories trying to stay warm when in cold weather. (But if they eat the same amount as always, they might lose weight as a result.)

Depending on where you are in the world, make sure to plan ahead for either extreme of temperature. Dogs can safely withstand both hot and cold weather to a certain extent – but you do want to ensure they’re still safe when you head outdoors.

Read more:

• Dogs And Heat: How To Keep Dogs Cool In Summer
• Heat Stroke In Dogs: Symptoms, Treatment & Prevention
• Dogs & Cold Weather: How Cold Is Too Cold For Dogs?
• 8 Best Tips On How To Protect Dog Paws In Snow
• Winter Dog Care: Protect Your Dog This Winter With These 8 Tips

Your dog might be having tooth pain

Another reason for your dog losing weight might is if they’re struggling with dental problems – or another disease that affects their mouth or gums.³

These can make it painful for them to chew or swallow foods – which make them more reluctant around mealtimes. (Which, with time, might make them lose weight.)

That’s why your dog’s smile is as important as their overall health – and dog dental care is an oft-neglected part of their routine.

Because left untreated, your buddy might be at risk of:

• Periodontal disease
• Gingivitis
• Stomatitis
• Tooth decay (from plaque buildup)
• …and a host of other diseases from bacterial infections that may spread to other parts of your dog’s body (including their lungs and heart)

Read more: Dog Dental Care: How To Get Your Dog The Best Smile Ever

Your dog’s struggling with an infection

If your dog’s eaten something that might be:

• Potentially toxic to them
• Old or spoiled
• From a contaminated surface (like a garbage dump)

…then they might lose weight from a bacterial infection – such as intestinal worms or other parasites. These critters “steal” any nutrition from any other healthy foods your dog might eat.⁴

Plus, your dog’s body is burning more calories to fight off the infection. Which, with time, can cause your dog to lose weight as a result. (Especially if your dog is too nauseous to eat.)

(In fact, vets even use the term “garbage gut” to describe gastroenteritis that’s caused when pets eat food or items they’ve scavenged out of the trash.⁵)

Now if you’re lucky, your dog’s digestive system might immediately trigger a vomiting response to get rid of any toxins. (Or as diarrhea instead.) Both of which mean that your dog also loses water from their system, which might turn up both as weight loss – but also dehydration.

In other cases, your dog might suffer an intestinal blockage instead – which can be deadly if left untreated.⁶

⚠️ So besides vomiting and diarrhea, watch out for signs like:

• Yelping when you touch their stomach
• Labored breathing
• If they’re more lethargic or less active than usual

Take your dog to a vet immediately if you notice any of these symptoms.

Read more:

• What Can Dogs Not Eat? 15 Foods Poisonous To Dogs
• Why Is My Dog Throwing Up? 8 Reasons Why & What To Do
• Diarrhea In Dogs: Top Causes And Treatments

💡This is where it makes sense to set clear boundaries with your friends and family what types of food are off-limits for your dog. (You might just have one feeding them something potentially toxic in secret.)

Likewise, tracking your dog’s outdoor adventures can actually help you to figure out where your dog is eating stuff they shouldn’t have.

Because with a dedicated dog GPS tracker, you can figure out where your dog’s getting fed – no matter how far they roam.

By monitoring their movements in real-time, you can figure out:

• If they’re being fed something potentially toxic by a neighbor
• If they’ve been raiding the local garbage dump
• If they’re coming in contact with toxic substances from specific parts of your neighborhood (like pesticides, snail bait, and similar)

It’s where your trusty Tractive device’s Heat Map & Location History can be a lifesaver.

With it, you now have a 24-day history of where your dog’s been hiding, hanging out, hunting, or just spending most of their time. (365 days on a Premium subscription!)

Which – in an emergency, like if they’ve gotten lost – can actually help you figure out where to look first.

Or, if you’re concerned about their dietary habits, figure out where they’ve been going to get fed or who’s been feeding them – so you can prevent them from venturing there.

(And then inform your neighbors not to give in to those puppy eyes.)

Discover Location History

Other medical reasons behind a dog losing weight

Now here’s where things get more serious. If you notice a sudden or drastic change in your dog’s weight, it could be due to these health conditions.

Digestive disorders

Both gastrointestinal (GI) and other issues can affect your dog’s digestive tract and mess with their ability to digest food and absorb nutrients.⁷ Which, with time, may cause your dog to lose weight, since they aren’t getting enough energy from the foods they eat.

Some GI disorders include:

• Lymphoma
• Inflammatory bowel diseases
• Intestinal blockages,
• and more

Likewise, another disorder known as exocrine pancreatic insuffiency (EPI) can mess with your dog’s digestion. When dogs have this condition, their pancreases don’t produce enough of the digestive enzymes they need to break down food well enough.

If your dog has generally lost their appetite, is vomiting, bloated, or generally seems weaker or lethargic, get in touch with your vet immediately.

Read more: Dealing With A Lethargic Dog: Signs, Steps & Symptoms

Metabolic disorders

Another cause of weight loss in dogs are health conditions that affect how their bodies burn calories.⁸ Including:

• Diabetes mellitus. When your dog’s body doesn’t have enough insulin, it can’t break down blood sugar for nutrition. So their body starts breaking down proteins and fats instead – which might lead to serious weight loss.
• Hyperthyroidism. While rare in dogs, their thyroid glands can sometimes go into overdrive – which increases how many calories they burn. If they burn more than they eat, they’ll lose weight.

• Liver and kidney diseases. When your dog’s liver and/or kidneys don’t work properly, they aren’t able to filter out any waste products created by their metabolism. This can turn up as nausea, poor appetite, and a loss of protein in their urine. All of which contribute to weight loss.
• Cancer, which changes the way our bodies use nutrients. Cancer cells grow and divide by taking away any energy your dog might’ve otherwise used. As a result, your dog might lose weight (as well as lose their appetite.)

Other health conditions

Besides digestive and metabolic disorders, your dog might also experience rapid weight loss if they’re experiencing:

• Heart disease, or cardiac cachexia. The exact causes of this weight loss are unknown, but it tends to speed up as your dog’s heart condition worsens.
• Loss of senses. As your dog grows older, their sense of smell might diminish. Now if they can’t smell their food anymore, their appetite might take a nosedive as well.
• Addison’s disease. In this condition, your dog’s body might not produce enough adrenal hormones, which can reduce their appetite. (And speed up weight loss.)

What to expect at a vet visit

If you’ve noticed your dog losing weight along with other signs of illness, it might be time to head to your vet.⁹

These include:

• Lethargy or weakness
• Labored breathing
• Vomiting or diarrhea
• Coughing or sneezing
• Increased thirst
• Increased urination

Your vet will begin by asking you questions about your dog’s medical history, appetite, changes in their environment, how much they eat per day, and what medications they might be on.

They might then physically examine your dog – followed by routine checkups, including your dog’s blood, fecal matter, and urine. (To rule out intestinal parasites.)

In more serious cases, your vet might recommend an ultrasound or other specialized tests, including even surgery.

This is all to uncover the underlying cause of your dog’s sudden weight loss – and address it from there on. So your vet might prescribe you:

• A change in diet, including higher-calorie dog foods or hypoallergenic dog foods
• Deworming pills to get rid of stomach parasites
• Antibiotics, in case your dog has a bacterial infection

Now a standard vet visit and checkup can be expensive – which is why it makes sense to prevent your dog’s condition from worsening in the first place.

So instead of waiting till it’s too late, here are…

3 ways to catch on early to your dog losing weight

Now that we’ve covered the reasons why your dog might be losing weight, here are a couple of ways to watch out for it – and catch it early before it worsens.

Know your dog’s body condition score

Before you whip out that weighing scale, it’s smart to inform yourself on what’s your dog’s ideal body condition score in the first place.

This is an easier process than weighing your dog and calculating their BMI, since you don’t necessarily need details like their age, breed, height, or weight.

Rather, start by:

• Viewing your dog’s body from above and the sides – how much visible fat or bones do you see?
• Feeling along your dog’s sides – can you feel their ribs or mostly fat?

Next, here’s a helpful chart to identify your dog’s body condition score:

For a dog that’s been losing weight gradually, they should be closer to an “Ideal Weight” appearance.

But if your dog’s been losing weight rapidly and seem to be more on the underweight side, it might be wise to drop by your vet.

Read more: Body Condition Score & BMI Calculator for Dogs

Monitor your dog’s diet & weight

Now if your dog’s only been losing weight gradually, it’s not usually a cause for concern. But if you’re observing them losing weight and also showing other signs of illness, it’s smart to take a hard look at their diet and figure out where they might be getting fed – and what they’re filling themselves up with.

⚠️ Even a bite, lick, or taste of common food products you’ll find in your kitchen could seriously poison your dog – or make them very sick.

Rapid and serious weight loss could be caused by almost any health problem. So as a rule of thumb:

• Weigh your dog around once a week
• Check their BMI score with a dog BMI calculator
• Get them to a vet if you notice they’re losing anywhere between 0.2-2 lbs/0.09-0.9 kg per week.

For a dog BMI calculator, you’ll need to plug in details like your dog’s age, sex, breed, height, and weight. Depending on your dog’s age, you’ll need to monitor their weight closely if:

• Your dog is a puppy, because they should actually be gaining weight as they grow! So any weight loss is cause for concern.
• Your dog is a senior dog. Older dogs are at higher risk for illnesses that cause them to lose weight.

So keep a weighing scale and a tape measure at the ready and head off to…

Check Your Dog’s BMI

If you’re finding your dog underweight as a result of their weight loss, head over to your local vet.

Track your dog’s activity

Different health conditions can cause your dog’s activity to drop – but also to spike!

Which is why vets recommend tracking observable behaviors like your dog’s everyday activity – or how often they’re on the move. (Or not.) So you can catch on early to a change from the norm.

Besides, most of your dog’s health conditions don’t develop overnight – but rather gradually, over time.

💡 And with their Activity Tracking numbers at hand, you now have actionable data to share with your vet – which can help prevent your dog’s condition from worsening.

Plus, you can also:

• Set goals for your dog’s daily activity – and stay motivated to hit them every time
• Compare how your dog is doing to other, similar dogs (by age and breed)
• Catch on to a change in your dog’s activity quicker and easier (which might signal something is wrong)
• Get a Health Alert in case your dog’s activity falls lower than normal

Discover Tractive GPS

💡You can also track your daily walks with your buddy with Tractive’s fun Walk feature. Log your adventures together and stay accountable to their health and well-being for the long term.

So – why is my dog losing weight? And what can I do?

Now the reasons your buddy might be shedding those pounds might not always be an emergency. But if they’re losing weight along with symptoms of illness (like vomiting, lethargy, or difficulties breathing), you’re best off heading to your vet.

Because the reasons for your dog losing weight might include:

• A change in diet, especially one your dog isn’t familiar or comfortable with yet.
• An increase in your dog’s activity, leading them to burn more calories than they eat – and lose weight.
• Something stressful in your dog’s environment, including moving houses, losing a loved one, or even adopting a new pet.
• Pregnancy, which might include appetite dips within weeks 1-6.
• Temperature that’s too hot or too cold

• Tooth pain, leading them to eat less as a result
• Infection from eating something toxic, spoiled, or from a contaminated surface
• Digestive disorders, including lymphoma, intestinal parasites, or inflammatory bowel disease
• Metabolic disorders, including liver or kidney diseases
• Other health conditions, including heart disease or a loss of their senses (especially smell)

Your vet might recommend keeping your dog on a deworming protocol or a monthly heartworm preventative.

💡At the same time, there’s a lot you can do to catch on to your dog’s condition early.

Like monitoring their:

• Daily intake, including from where they’re getting fed from around your neighborhood (whether that’s at a neighbor’s or at your community garbage dump)
• Weekly weight and BMI, using a BMI dog calculator, a weighing scale, and a measuring tape.
• Daily activity, which can help you catch on early to a dip in their active minutes – and take action early by getting them to a vet for a checkup. (And not an expensive surgery instead!)

And the best part? You can monitor all three on just one device – built with love for dogs around the world, and the dog parents who’ve chosen to take an active role in their buddies’ well-being.

Stay on top of your dog’s wellness

See how they’re doing at a glance with Wellness Score. Set goals. Compare with dogs like yours. Monitor sleep. Detect issues and keep them healthy.

Discover Tractive GPS

Wondering why your dog is losing weight – while still eating normally? Here’s a quick video covering the facts:

And if you’ve liked this post, share it with a friend or a loved one – and let’s help build a safer, kinder world for our furry friends together.

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Your furry friend’s health and wellbeing means as much as to us as it does to you. So we’ve made it a priority to only share medically-relevant content on our blog.

This post was checked, double-checked, and medically verified by Georgia-based vet, Dr. Dwight Alleyne.

Originally from Long Island, New York, Dr. Alleyne began his career at a no-kill animal shelter before becoming a licensed veterinary technician. He graduated from Cornell University Veterinary College in 2006 and completed an internship at Purdue University.

Now practicing in Georgia, Dr. Alleyne specializes in soft tissue surgery and ultrasounds. He also writes pet health articles on his website, “The Animal Doctor Blog” (www.anmldrblog.com).