Reasons Your Dog Is Gaining Weight [+ Weight Loss Tips]

Reasons Your Dog Is Gaining Weight [+ Weight Loss Tips]

If your dog is gaining weight, and you’re not sure why, it’s natural to be worried and anxious. There are several reasons why dogs put on weight, which we’ll explore in detail in this guide.

4 Non-Diet (Medical) Reasons Your Dog Might be Gaining Weight

If you’re asking yourself, ‘Why is my dog gaining weight so fast?’ here are some possible medical causes:

Cause #1: Undiagnosed Hypothyroidism

Hypothyroidism is a condition in which the thyroid gland doesn't produce enough thyroid hormone. “You can loosely associate hypothyroidism with the furnace of the pet’s body not burning hot enough,” explains Dr. Michel Selmer, DVM, from the Advanced Animal Care Center in Huntington Station, New York. “When there is decreased thyroid function, that’s when pets gain weight.”

Hypothyroidism slows down the entire metabolism, which in turn leads to weight gain. “Even if a dog has hypothyroidism and its owner cuts calories, the dog will still gain weight since food is not the cause of the weight gain,” Selmer explains.

Cause #2: Heart Disease and Water Retention

Cushing’s disease—an endocrine disorder that causes an increase in cortisol production—can cause weight gain due to bloating. “This might not always translate into a real larger number on the scale but the dog will appear bigger,” Selmer says. “With Cushing’s disease, dogs lose muscle mass, which means the scale often stays the same but you will see a skinny dog with a big potbelly who is losing hair.” A dog suffering from Cushing’s disease may also exhibit skin problems, be thirsty and urinate excessively.

Other health issues, including heart disease and cancer, can also cause bloating. “For example, with heart disease, a dog’s heart is not functioning properly to effectively pump blood through the body—this causes fluid to leak through vessels and into the abdomen and/or the chest,” according to Selmer. “This in turn makes the belly expand and looks like the animal has gained weight.” This is dangerous because diseases that can cause dogs to look like they gained weight can be life threatening or life shortening, Selmer explains.

Cause #3: Prescription Drugs

A number of prescription drugs can cause weight gain, especially if given for long periods of time. “For example, Prednisone can cause weight gain because it mimics Cushing’s disease when given for too long or in too high dosages,” Selmer explains.

The solution? If your dog is gaining weight due to medication, your vet might look into switching to a different drug or trying a different approach. “If a veterinarian sees negative side effects, they should look for alternative modes of therapy or different philosophy of care, such as Traditional Chinese Veterinary Medicine,” Selmer says.

Cause #4: Intestinal Parasites

Parasites can often cause a "potbelly" looking appearance due to an excessive build up of fluids near the area of infestations. This is typically associated with parasites that find themselves in the abdominal walls and intestines. Usually you will see this in puppies with underdeveloped immune systems.

Other Common Reasons Your Dog is Getting Fat

If you find yourself saying, ‘My dog is gaining weight for no reason’ or ‘My dog keeps gaining weight’ there are multiple non-medical reasons why dogs put on weight. These include:

Feeding your dog too much food

Just like humans, dogs will gain weight if they eat too much. Take care to control portion sizes, limit treats and snacks, and pay attention to feeding guidelines to make sure you’re not giving your dog too much food.

Not switching Your Dog’s Food With Age

As dogs get older, they have different nutritional requirements. Puppies should have a different diet from older dogs. Puppy food contains more calories than adult food because it is designed to promote growth and development. When your puppy reaches adulthood, switch to adult food, which is lower in calories. Senior dog food, which is suitable for dogs aged over 7-8 years old, usually contains fewer calories, it is high in fiber and it provides sufficient protein and fat for dogs as they age.

Recommended Reading: Rotational Feed For Dogs: Benefits and How-To Switch Your Dog's Food Safely

Wrong food for diabetes

If your dog has diabetes, it is essential to ensure that your furry friend has a healthy diet and that its calorie intake is suitable for its size and activity levels. Obesity is a major risk factor for diabetes in dogs. If your dog is diabetic, it’s wise to seek advice from your vet and follow a plan to ensure you choose the right foods and you don’t overfeed your dog. Losing weight can help to alleviate symptoms. High-fiber, low-fat diets are usually recommended to prevent weight gain in dogs with diabetes.

Lack of exercise

Exercise burns calories and it plays an integral role in promoting optimum physical and mental health in dogs. Some breeds need more exercise than others but all dogs can benefit from a daily walk and playtime in the garden. A lack of exercise can increase the risk of weight gain and obesity in dogs. If you’re unsure how much exercise your dog should be getting, ask your vet for advice.

Helpful Tips to Help Your Dog Lose Weight

Simple steps to help your dog lose weight:

  • Make sure your dog has a healthy, balanced diet
  • Stick to recommended serving sizes for your dog’s breed, age and weight
  • Ensure your dog exercises regularly
  • Choose high-quality foods
  • Spend time playing together
  • Limit treats and snacking
  • Introduce changes to your dog’s diet gradually
  • Seek advice from your vet if your dog gains weight rapidly or they seem to be putting on weight for no clear reason

Try Feeding Your Dog Human-Grade Food to Fight Weight Gain

Opting for high-quality, human-grade foods for dogs is an excellent way to encourage weight loss and prevent weight gain. Here are some low-calorie dog food products we recommend from The Honest Kitchen:

Health Disclaimer: This post is educational in nature and doesn’t constitute health advice. Please consult your pet's veterinarian or other healthcare professional for specific guidance on this topic.


Diana Bocco

Diana Bocco is a full-time writer and avid adventurer. She's gone hiking in Siberia, snorkeling in Thailand, and canoeing in the Mekong River. She also loves caves and has been known to get lost in one or five around the world. Diana's work has been published in the Discovery Channel website, Yahoo!, Popular Mechanics, and more. You can read more of her work on her website at
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