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Causes of Rapid Weight Gain in Dogs

Rapid Weight Gain in Dogs

While weight loss in dogs is considered more worrisome than weight gain, it's still important investigating what causes sudden, rapid weight gain in dogs. Weight gain is considered when a dog's caloric intake exceeds his metabolic demands. In other words, there is an imbalance between the dog's energy intake and energy burning. Generally, weight gain in dogs deserves evaluation when the weight gain consists of more than 10 percent of body weight. Obesity instead is generally considered when the weight gain exceeds 15 percent of the ideal body weight set by standardized weight charts. While being fed excess food and not exercising enough is a main cause of obesity in dogs, there are also several medical conditions that may cause rapid weight gain in dogs.

dog increased weight

Weight Gain and Excess Eating

When there is weight gain and excess eating, one may gain reassurance in knowing that that there is an explanation for the weight gain as the intake of excess food is to blame for the fat accumulation; however, there are medical conditions that can be associated with excess eating in dogs (polyphagia) that warrant diagnostic evaluation.

Weight gain due to excess eating may be due to boredom, overeating (it's easy to get carried away with doling out table scraps) and reduced physical activity, but it also can be due to other causes.

Certain drugs, for instance, may cause increased appetite. For example, phenobarbital, a popular anti-seizure drug given at high dosages may cause excess eating and so can steroids.

Health conditions that may increase appetite may include endocrine disorders such as Cushing's disease, acromegaly and diabetes.

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"If you feed less, your dog may be hungry because the stomach never feels full. If this is a problem, you can add canned green beans (low sodium) or canned pumpkin (not the pie filling kind), to bulk up the fiber and add only a few calories. This will make the dog feel fuller." Dr. Wally

Weight Gain and Reduced/Normal Appetite

If your dog is gaining pounds by the day, but yet he is eating normally or perhaps he's even not eating enough, things may not add up. It could be that you are overfeeding or that your dog has a slow metabolism. Some dogs may be genetically predisposed to obesity. For example, some dog breeds are particularly predisposed to gaining weight such as basset hounds, dachshunds, beagles, cocker spaniels, and Labrador retrievers.

Age can also be a factor considering that, as dogs age, they undergo a reduced metabolic rate. Also, senior dogs suffering from orthopedic problems may move around less, yet dog owners fail to reduce caloric intake. If your dog is moving less around due to illness, mobility problems or old age, consult with your vet for a quick calculation of your dog's caloric needs. Reduced metabolic rates can also be caused by medical conditions such as hypothyroidism.

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Weight Gain due to Enlargements

Sometimes the weight gain may not be due to increased body fat, but rather some enlargement or swelling of dog body parts. In many cases, this may be very noticeable, but sometimes not. For instance, a dog may gain pounds from ascites; the accumulation of fluid in the dog's abdomen. Dogs with ascites typically present an enlarged belly. Ascites in dogs may be due to serious conditions such as malfunctioning organs.

Another cause of weight gain may be edema, the buildup of fluids, which can be seen under the form of swollen legs in dogs with congestive heart failure. Organomegaly is also a cause of weight gain. In this case, a dog's organs such as the liver or spleen may enlarge.

Less concerning, but worthy of mentioning, dogs may gain weight from an increase in lean body mass (the total weight of your dog's body minus all fat mass) as seen from increased exercise in athletic dogs (greyhounds, sled dogs etc).

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Weight Gain and Neutering

Will my dog get fat and lazy after neutering or spaying? This is often a main concern for dog owners. Sure the removal of reproductive hormones may slow down a dog's metabolism. According to board-certified veterinarian, Dr. Christopher G. Byers, the changes in hormones occurring after a pet is altered affect the satiety center in the dog's brain.

A study showed that female beagles were eating more food and gaining more weight after being spayed. Dog owners can prevent their recently spayed/neutered dogs from gaining weight rapidly by reducing caloric intake by up to 30 percent after spaying. Consult with your vet for specific dietary recommendations after spaying or neutering your dog. 

"Spayed (dogs) have a lower metabolic rate and therefore need less food intake, if you continue to feed them the same amount of food after the spay there is a high risk that they will put on weight. Having understood this point all you have to do is to modify their diet, monitor their weight on a monthly basis and make changes to their diet accordingly so that they stay trim." ~Dr. Scott Nimmo


  • DVM360, Obesity in dogs, Part 1: Exploring the causes and consequences of canine obesity
  • Jeusette I, Detilleux J, Cuvelier C, et al. Ad libitum feeding following ovariectomy in female Beagle dogs: effect on maintenance energy requirement and on blood metabolites. J Anim Physiol Anim Nutr (Berl) 2004;88:117-121.

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  • Flickr, Creative Commons, Dale My buddy Andy CCBY2.0

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