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Ask a Vet: Does Spaying Make Dogs Fat?

Spaying Makes Dogs Fat

Whether spaying makes dogs fat is something that many dog owners may wonder about and this can also cause a reluctance to get dogs spayed. "Should I spay my dog if that means her getting fat and lazy?" "What can be done to prevent spayed dog from packing up pounds?" These are important questions. The good news is that dogs do not get fat unless you feed them a whole lot and fail to properly exercise them. This means that you can be in control of whether your dog will get fat or not after spaying. Following is important information about the effects of spaying on a dog provided by veterinarian Dr. Ivana Crnec.

fat dog

Weight Gain in Spayed Dogs 

Obesity is a common problem among dogs worldwide. It has been estimated that 34 percent of all dogs are overweight or obese. It is most simply defined as an excess of body fat which frequently results in adverse health effects and increased risk for certain diseases.

Obesity is therefore a severe health issue. In addition of applying unnecessary and uncomfortable tension on the joints, excessive weight gain is a predisposing factor to a plethora of health problems such as heart diseases, high blood pressure, liver issues, diabetes mellitus, respiratory disorders, constipation and certain types of cancer. But what is the leading cause of obesity in dogs?

Statistics show that spayed/neutered dogs are more than twice as likely to become overweight or obese compared to sexually intact dogs. However, saying that dogs become overweight or obese just by being spayed/neutered is an oversimplification.

When it comes to gaining weight dogs and humans are quite similar – both gain weight if they eat too much while exercising too little or if they are genetically programmed to be overweight.

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Why Does Spaying Make Dogs Fat?

So why does spaying make dogs fat? There are two leading theories that explain why spayed/neutered dogs are at higher risk of gaining weight: hormonal changes and altered metabolism and energy requirements.

Hormonal Changes 

Spaying and neutering result in hormonal changes. Certain hormones, like estradiol and testosterone, are no longer secreted while others, like leptin and insulin are shifted. Leptin is a hormone that regulates the appetite and food intake while insulin controls blood sugar levels. These hormonal changes lead to increased appetite and slower metabolism. When a dog’s appetite increases and its metabolic rate decreases, weight gain is likely to occur.

Decreased sex hormones, particularly in females, make the brain less likely to realize when the stomach is full. Simply put, the brain’s capacity to differentiate hunger from satiation is diminished. Additionally, the lack of hormones makes dogs more lethargic and with reduced roaming urge and willingness to be physically active.

All in all, the lack of hormones makes the dog’s appetite control mechanisms incapable of balancing the caloric intake with the energy expenditure.

Altered Metabolism/Energy Requirements

For a very long time it was believed that the main culprit that leads to weight gain in spayed dogs is the reduced metabolic rate. When the metabolic rate is reduced, the food calories are likely to be burned as energy and more likely to be diverted to the body’s fat stores. However, if instead of expressing the metabolic rate on total body weight it is expressed on lean body mass, there is no difference between fixed ad intact dogs.

Simply put, the difference between the total and lean body mass is made up by the fat stores. Since fat stores are metabolically inactive including them in the overall metabolic rate gives erroneously reduced rates.

Therefore, the weight gain in spayed/neutered dogs is more likely to be due to decreased energy requirements. For example, the daily calorie requirement for a 20 kg border collie declines from 175kcal/kg to 97kcal/kg after spaying/neutering.

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What Research Says 

On the 15th of July, 2013, the Journal of the American Veterinary Medical Association (JAVMA) published a review paper that described the connection between spaying or neutering and weight gain. During the study, the researchers reviewed the medical records of 1930 spayed and neutered dogs: 782 of them were spayed/neutered while less than 6 months old, 861 were spayed/neutered when between 6 months and 1 year of age and 287 were spayed/neutered when older than 1 year of age but younger than 5 years.

Their medical records were compared to the medical records of 1669 intact dogs. Each dog was continually followed at least 10 years or until diagnosed as overweight or obese.

At the end of the study it was confirmed that there really is a link between spaying and neutering and increased risk of weight gain. However, that link was classified as significant only during the first two years after the spaying/neutering procedure.

Additionally, the study confirmed that there is no correlation between the age at which a dog is spayed/neutered and the increased risk of gaining weight. Simply put, the timing of the spaying/neutering procedure has no effect on whether or not the spayed/neutered dog will be subsequently diagnosed as overweight or obese.

Other Causes for Weigh Gain in Dogs

The four most common reasons for gaining weight in dogs are:

  1. Undiagnosed hypothyroidism
  2. Wrong diet
  3. Water retention and bloating
  4. Using certain prescription drugs.


Simply put, hypothyroidism is a medical condition characterized by decreased production of thyroid hormones. Decreased thyroid function is directly linked with weight gain. This is because the lack of thyroid hormones slows down the metabolism. Regardless of what they eat and how much they exercise, dogs with hypothyroidism are quite likely to gain weight.

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Wrong Diet

As dogs age, their diet needs to be adjusted to their needs. The nutritional requirements for a puppy are different than the nutritional needs for a senior dog. In addition of the life stage, the dog’s activity level also plays an important role in calculating its nutritional needs.

Water Retention and Bloating

Water retention and bloating can develop due to a plethora of medical conditions – Cushing’s disease (increased cortisol production), heart conditions and some types of cancer.

Prescription Drugs

Certain drugs when used for either too long or in high doses are likely to cause weight gain. Corticosteroids are the most popular weight gain causing drug.

The Bottom Line 

While it is true that packing on pounds is easier for spayed/neutered dogs, it is not inevitable. Spaying and neutering alter the dog’s metabolism and appetite. The metabolism is slowed down and the appetite is increased. When these two changes are combined, weight gain is likely to occur.

Another factor that contributes to unnecessary weight gain is the decreased physical activity significant particularly in male dogs. Due to their hormonal drives and efforts to find mating partners, intact male dogs tend to move a lot. After neutering, the urge to roam decreases drastically.

As previously stated weight gain is not inevitable. Proper diet and exercise regimen can go a long way in keeping your spayed/neutered dog lean and healthy. When saying proper diet we refer to two factors – healthy food and portion control.

About the Author

Dr. Ivana Crnec is a graduate of the University Sv. Kliment Ohridski’s Faculty of Veterinary Medicine in Bitola, Republic of Macedonia. She currently practices as a veterinarian in Bitola and is completing her postgraduate studies in the Pathology of Domestic Carnivores at the Faculty of Veterinary Medicine in Zagreb, Croatia. Ivana’s research has been published in international journals, and she regularly attends international veterinary conferences.

ivana crnec

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