Sudden Dog Weight Gain: 7 Possible Causes

Overweight Jack Russell being held

When it comes to sudden weight gain in dogs, your veterinarian is almost always going to check your dog’s diet first. How much is your dog eating? Have you changed your dog’s diet recently? What sorts of treats and table scraps does your dog get?

But what if your dog gained weight suddenly without a dietary change? We’ve got the first two steps down! We’ve noticed the weight gain, and we’ve reviewed the diet. But what comes next? 

There are medical reasons for sudden weight gain in dogs, and it’s important to rule those out, too.

Noticing Sudden Dog Weight Gain: Signs and Symptoms

Obviously, you might notice that your dog is looking a bit bigger or that the number on the scale at the veterinary office has increased. However, some medical causes of weight gain have other symptoms that accompany the dog’s changing weight. 

Other signs you may notice include:

  • Change to appetite (increased or decreased, depending on the cause)
  • Excessive panting
  • Excessive drinking and urinating
  • Hair loss or hair thinning on the trunk of the body and/or tail (“rat tail”)
  • Chronic skin infections
  • Dark-colored areas on the skin (hyperpigmentation)
  • Mineralization in the skin (calcinosis cutis)
  • Bloated or “pot-bellied” abdomen
  • Lethargy or low activity level

If your dog is having weight gain due to overeating, they’re not usually going to have the additional symptoms listed above. 

However, some dogs who’ve gained weight without an underlying medical reason will pant more and engage less in physical activity. Obesity makes dogs prone to overheating and causes more stress on their joints when active.

7 Causes of Sudden Weight Gain in Dogs

Aside from excess caloric intake and decreased physical activity, there are medical reasons and lifestyle changes that may cause your dog to gain weight quickly. 


Hypothyroidism is a hormonal condition that decreases your dog’s metabolic rate. As a result, you may notice your dog gaining weight despite no changes in their eating habits. It’s also possible to see an appetite decrease in the face of weight gain. Some pet parents notice that their hypothyroid dog is overweight but doesn’t eat much.

Cushing’s Disease

Hyperadrenocorticism, also known as Cushing’s disease is a hormonal condition that increases your dog’s appetite. It can also cause enlargement of the liver, which contributes to the pot-bellied appearance to the abdomen. Pet parents of dogs with Cushing’s often notice that their dog is gaining weight and panting more, drinking more, peeing more, and eating more.

Orthopedic Conditions

Conditions like arthritis or a healing bone fracture may make it difficult for your dog to get around. As a result of decreased activity levels, your dog may gain weight.

Medication Use

Long-term use of steroids like prednisone can increase your dog’s appetite, leading to weight gain. The antiepileptic drug phenobarbital can also increase appetite.

Getting Spayed or Neutered

The surgery itself does not cause your dog to gain weight. However, your pet’s energy requirements decrease after they’re altered [1]. As a result, you should be adjusting their dietary intake. Your veterinarian can help you plan to avoid weight gain in your altered dog.


Pregnant dogs should have a weight increase of 15-25 percent in the last month of pregnancy [2]. Speak with your veterinarian about how to feed a pregnant dog.


Sudden weight gain in older dogs may occur due to a decreased metabolic rate. Senior dogs generally have a lower energy requirement than their younger counterparts. If you haven’t adjusted your older dog’s food, you may notice them gaining weight.

Sudden Weight Gain Vs. Bloating in Dogs

There is a difference between looking bloated and actually gaining weight. Looking bloated means your pet’s abdomen appears stretched compared to normal. Your dog’s abdomen can look bloated without a change in their weight. Potential causes of bloating include:

  • Binge eating: If your dog gets into the pantry and eats the whole bag of dog food, they may have a bloated appearance.
  • Gastric dilatation and volvulus (GDV): GDV most commonly affects large, deep-chested dogs. The stomach fills with gas or food (gastric dilatation/bloat) and then twists on itself (volvulus). One of the most common symptoms is nonproductive retching. This is an emergency!
  • Ascites: Fluid build-up within the abdomen (ascites) can cause your dog to appear bloated. Ascites has multiple potential causes, with heart failure or bleeding splenic masses among the more common causes in dogs.
  • Tumors:: A growth within the abdomen may cause a bloated appearance.

What to Do if Your Dog Is Gaining Weight Rapidly

If your dog is gaining weight quickly, you should call your veterinarian for an appointment. Even if the issue is simply that you’re overfeeding your pet, your veterinarian can rule out underlying conditions and help you develop a healthy weight loss plan.

Information to provide your veterinarian includes:

  • Exact amounts and types of foods and treats you’re feeding
  • How long you’ve noticed the weight gain occurring
  • If you’ve noticed changes to appetite, coat quality, skin health, urination, or water intake

Your veterinarian will perform a physical exam and likely recommend baseline blood work and urine testing. Based on these results, additional blood tests may be recommended to rule out conditions like Cushing’s disease or hypothyroidism.

If your veterinarian suspects an issue within the abdomen, such as binge-eating or fluid build-up, they may recommend an X-ray or an ultrasound of your dog’s abdomen. X-rays will be recommended if your veterinarian suspects an orthopedic condition like arthritis.

If your dog appears suddenly bloated and is vomiting, retching non productively, having difficulty breathing, coughing, is unable to stand, or you’re otherwise worried that they’re not acting like themselves, seek emergency care as quickly as possible.

Coming up With a Treatment Plan

Pet owner discussing weight gain with vet

Your veterinarian’s treatment plan for rapid weight gain in dogs will depend on the underlying cause.

If your dog’s rapid weight gain is due to overfeeding without an underlying medical cause, your veterinarian will focus on control of caloric intake and increasing physical activity. Dietary changes may involve feeding less of your dog’s current food, limiting treats, or a prescription weight loss diet. Other causes of sudden weight gain that require dietary management include getting altered (spay/neuter), pregnancy, and aging.

Some causes of sudden weight gain can be controlled with oral medications. For example, Cushing’s disease is usually controlled with the medication trilostane. Hypothyroidism is usually controlled with the medication levothyroxine.

For dogs gaining weight due to painful orthopedic conditions that limit their mobility, the focus will be on pain control. This may include nonsteroidal anti-inflammatory drugs (NSAIDs) like carprofen or grapiprant, joint supplements, or other medications.

An overweight dog lives anywhere from 5 months to over 2 years less than a lean dog, depending on their breed [3]. If you are concerned that your dog is suddenly gaining weight, follow your veterinarian’s recommendations to identify an underlying cause and get your dog back on the right track.



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