Does Spaying and Neutering Cause Weight Gain in Dogs and Cats?

Published Sep. 30, 2013

Like any medical procedure, the need to spay or neuter should be addressed on a case by case basis. In my experience, most dog owners feel the benefits of spay/neuter (preventing unwanted litters and heat cycles; reduced aggression, roaming, and/or marking; eliminating or reducing the risk of certain diseases) outweigh the potential downsides (risk/expense of surgery and an increased chance of other diseases).

Once the decision to spay/neuter is made, the question of when to perform the surgery then arises. Again, the pros and cons of spay/neuter before versus after puberty need to be considered. I tend to recommend prepubertal spay/neuter to maximize the procedure’s benefits. When spayed prior to the onset of the first heat cycle, a female risk of mammary (breast) cancer falls to almost zero. Waiting just two heat cycles virtually negates the benefit of surgery, in this regard at least. Also, the effect of neutering on aggression in male dogs is much better when the surgery is performed before aggression begins (in other words, before puberty) versus after the behavior has developed.

In my opinion, one of the biggest downsides of spay/neuter is an increase in the incidence of weight gain. This can be prevented and controlled with relative ease by reducing the number of calories a dog takes in and providing ample opportunities to exercise, but I’ve always wondered if early age spay/neuter might make the tendency for weight gain even worse. If so, this might be reason to consider delaying the surgery, at least in those cases where obesity was of particular concern.

A paper published in the July 15, 2013, issue of the Journal of the American Veterinary Medical Association (JAVMA) put those fears to rest. The study looked at the medical records of 1,930 dogs that were spayed or neutered at ≤ 6 months of age (782), > 6 months to ≤ 1 year of age (861), or > 1 to ≤ 5 years of age (287) and compared them to the medical records of 1669 hormonally intact dogs. The dogs’ records were followed for at least ten years or until they were diagnosed as being either overweight or obese.

This study confirmed the link between spay/neuter and an increased risk for weight gain, but this relationship was only statistically significant during the first two years after the surgery was performed. Also, the age at which a dog was spayed or neutered had no effect on whether or not he or she was subsequently diagnosed as being overweight or obese.

Overall, this paper is good news for people who elect to spay and neuter their dogs. Yes, the tendency to gain weight needs to be addressed, but the timing of the surgery doesn’t affect the outcome.