Why Your Dog’s Losing Weight and What to Do

Jennifer Coates, DVM
By Jennifer Coates, DVM on Dec. 15, 2022

It’s normal for a dog’s weight to vary a little bit over time. If you change their diet to one that isn’t to their liking, they’ll probably lose a few pounds. Or maybe they are staying inside more during the winter; in this case, they’ll probably gain a little.

But what about a dog that keeps losing weight and you don’t know why? Unexplained weight loss can be the first sign that a health problem is brewing.

Why Is My Dog Losing Weight?

Weight loss in dogs has many causes. Problems with a dog’s diet, environment, and health could all be to blame. Here are a few of the most common causes of unexplained weight loss:

  • A problem with their food: Dogs may eat less when there is something they don’t like about their food. A change in diet may be to blame, or perhaps a large bag of food has started to go bad before your dog has finished it. Feeding too little or giving your dog low-quality dog food can also lead to weight loss.

  • Stress: A dog that’s anxious or stressed may find it hard to relax and eat because they feel like they always need to be on alert.

  • Exercise: Dogs that start exercising more but don’t take in more calories will lose weight.

  • The environment: Dogs require extra energy to stay warm when they spend lots of time in the cold. Conversely, hot temperatures can reduce a dog’s appetite.

  • Reproduction: Pregnancy and lactation (nursing puppies) put extra nutritional demands on dogs. If they don’t take in more calories, they will lose weight.

  • Dental disease and other oral problems: Any problem that makes chewing and swallowing painful or difficult will discourage a dog from eating.

  • Intestinal worms and other parasites: Parasites get their nutrition from their hosts, which can lead to weight loss in dogs.

  • Cancer: Cancer cells use energy to grow and divide, and this means that the energy is not available to the dog, so they often lose weight. Cancer can also directly affect a dog’s digestive system and appetite.

  • Gastrointestinal (GI) disorders: Problems that affect the functioning of the digestive tract can reduce a dog’s appetite or their ability to digest and absorb nutrients. Inflammatory bowel disease, lymphoma, adverse food reactions, or partial intestinal blockages could be to blame.

  • Nasal problems: Any condition that affects a dog’s ability to smell their food can lead to a reduced appetite.

  • Diabetes mellitus: The changes in glucose metabolism seen with diabetes mellitus frequently lead to weight loss in dogs, even when they have a good appetite.

  • Exocrine pancreatic insufficiency (EPI): When dogs have EPI, they don’t produce enough of the digestive enzymes needed to break down food and absorb nutrients.

  • Infections: Bacterial, viral, or fungal infections can directly affect the GI tract and lead to weight loss. Fighting an infection anywhere in the body requires extra energy, and if dogs don’t eat more, they will lose weight.

  • Kidney and liver disease: When the kidneys or liver don’t function properly, waste products of metabolism build up in the bloodstream, which can make a dog nauseated and not feel like eating. Dogs with kidney disease may also lose protein in their urine, which can lead to weight loss.

  • Heart disease: Weight loss is common as heart disease progresses. The exact causes of this are unknown, but the condition goes by the name cardiac cachexia.

  • Addison’s disease: Dogs with Addison’s disease (hypoadrenocorticism) don’t produce enough of certain types of adrenal hormones, which can lead to poor appetite and weight loss.

  • Hyperthyroidism: Although hyperthyroidism is rare in dogs, it can increase their metabolic rate and lead to weight loss.

  • Neurologic conditions: Any disease that adversely affects a dog’s ability to eat and swallow can result in weight loss.

Is My Dog Too Skinny?

Regularly checking your dog’s weight by using an accurate digital scale is the best way to monitor for weight loss or gain. However, evaluating a dog’s body condition score can also help you determine if your dog is too skinny. In general, a dog might be too skinny if:

  • You can easily see their ribs or other bony points.

  • When looking down from the top, they have a very pronounced waist.

  • When looking from the side, they have an exaggerated abdominal tuck.

When to See Your Vet About Your Dog’s Weight Loss

A little bit of weight loss isn’t always an emergency. As long as your dog doesn’t have any other signs of illness, you could try to change their diet or environment to see if it solves the problem. But there are times when you should get your dog to a veterinarian ASAP:

  1. Puppies shouldn’t lose weight! As they grow, puppies should be gaining weight, so call your veterinarian immediately if your puppy is losing weight or getting too skinny.

  2. Weight loss in a dog that’s older or has an underlying health problem is always concerning. The risk of serious diseases that cause weight loss increases as dogs get older.

  3. Weight loss combined with symptoms of illness is never normal. Make an appointment with your veterinarian if your dog has difficulty breathing, vomiting, diarrhea, coughing, sneezing, weakness, lethargy, increased thirst and urination, or any other worrisome symptoms. If your dog’s symptoms are severe, call a vet immediately to determine if you should head to the clinic right away.

  4. Rapid or pronounced weight loss should always get your attention. Any health problem can lead to serious weight loss. Make an appointment with your veterinarian if your dog has lost more than 10% of their normal body weight or is losing 2% or more of their body weight per week. Here’s what that can look like for dogs of different sizes:

Serious Weight Loss in Dogs

Normal Weight in Pounds

Current Weight in Pounds

Rapid Weight Loss



0.2 pounds/week



0.5 pounds/ week



1 pound/week



1.5 pounds/week



2 pounds/week


How Do Vets Treat Unexplained Weight Loss in Dogs?

A veterinarian will start by asking you a lot of questions about your dog’s diet, appetite, environment, behavior, medical history, and any current medications (including parasite preventives) or supplements that you are giving. They will also determine how many calories your dog is taking in each day and if this amount should be meeting their energy needs.

Next, they will perform a complete physical examination and use the information they uncover to recommend treatment or further diagnostic testing. A basic laboratory workup includes a fecal examination, bloodwork, and a urinalysis. Additional testing can involve x-rays, ultrasound examinations, specialized lab tests for specific health problems, endoscopy, exploratory surgery, and tissue biopsies.

Whenever possible, veterinarians will recommend treatment for a dog’s weight loss that aims to cure or at least improve its underlying cause. For example, they will prescribe a dewormer if a dog has intestinal parasites, dental care for damaged teeth, or antibiotics for a bacterial infection. Oftentimes, a change in diet can also help dogs regain the weight they’ve lost. Options include:

  • High-calorie, nutrient-dense dog foods for generalized weight gain

  • Highly digestible diets when GI function is impaired

  • Dog foods with added fiber may be appropriate for some types of GI problems or for dogs with diabetes

  • Hypoallergenic dog foods made from novel ingredients, hydrolyzed proteins, or individual amino acids for food allergies and intolerances

  • Disease-specific diets like those designed to help manage kidney or liver disease

The right food and other treatments will depend on the specifics of your dog’s case. Don’t wait too long to get your dog the care they need. It’s easier to manage a dog’s weight loss when it hasn’t had a chance to progress too far.

Featured Image: iStock/Capuski

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Jennifer Coates, DVM


Jennifer Coates, DVM


Dr. Jennifer Coates is an accomplished veterinarian, writer, editor, and consultant with years of experience in the fields of veterinary...

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