Do spayed and neutered cats put on weight?

by Michael Broad · November 21, 2021

The answer is that spayed and neutered domestic cats ‘tended to be heavier than those that weren’t’. So, the answer is, yes, spayed and neutered cats do put on weight but the experts can’t fully explain why as at 2021 based in my research. Although Dr Bruce Fogle very clearly states in this book Complete Cat Care that ‘when a cat is neutered, the metabolic rate decreases by about 20 percent, so neutered cats require less food’. Combine this with a full-time indoor life and addictive dry cat food and you have the recipe for the so-called feline obesity epidemic that vets talk about.

In a study of Dec 2004 on the effects of body fat by neutering cats_B they found: “Neutered cats gained significantly more body fat and body weight (53.80 ± 5.79%) than sexually intact cats (27.11 ± 5.79%) during the study”. This happened when the energy expenditure and food intake was the same as the control group of cats who were not sterilised. The recommendation was to feed a low-fat diet.

Another study_A dated June 2002, states that “Although it has been demonstrated that food intake increases 3 months after neutering, it is not clear whether an increase in food intake is the primary cause of body weight gain in neutered cats”. So, an increase in weight post-sterilisation is partly due to increased food intake.

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Spaying and neutering puts on weight but we are not sure why exactly. Photo: Catsite as amended.

The quote short below comes from the CBC.com website. The author refers to a massive AVMA study on domestic cat weight. The study involved more than 19 million cats in the US and Canada so the conclusion is very solid although when you read the summary of the study on the AVMA website the authors write:

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Mean [body weight of shorthair, medium hair and longhair domestic cats] peaked at 8 years and was subjectively higher for neutered than for sexually intact cats.

The phrase ‘subjectively higher’ is surprising for scientists to use as it indicates that they are unable to provide hard data. They may simply be repeating anecdotal evidence.

It is also surprising that it is hard to find a clean and clear reason why spayed and neutered cats put on weight.

Dr Jennifer Coates on petmd.com honestly writes that she can’t come up with a good explanation as to why domestic cats eat more (as shown in 2 studies) post-surgery when given free access to food. The cats don’t need more calories because they are not burning more calories so why were they eating more in the studies? She guesses that it is something to do with their lack of hormones – oestrogen for females and testosterone for males – after the surgery. At least she tells us that weight gain is due to eating more.

“The study on male cats showed a dramatic increase in food intake in some cats during the first week post-surgery, with some cats experiencing a 10 percent increase in body weight.”

Another veterinary source¹ says that spaying female cats may slow their metabolism. They don’t make any reference to male cats putting on weight after neutering. This information conflicts with Dr Coates’ statement which does not help me.

However, my distinct impression is that both male a female cats may put on weight post-surgery. I wonder if the problem is more prevalent for female cats? It is interesting to note that menopausal women tend to put on weight. During menopause their production of oestrogen is greatly reduced. This information cross references what Dr Coates states about weight gain being linked to hormonal change. In women a lack of oestrogen causes the body to use starches and blood sugar less effectively resulting on increased fat storage. Also, oestrogen hormone therapy increases a woman’s resting metabolic rate although I can’t find out why.

The recommendation is food portion control for your cat post-surgery if she or he was free feeding before the surgery. Dr Coates recommends restricting food portions for up to five months after the spaying and neutering operations. Based on Dr Fogle’s observation mentioned above neutered cars require less food. They also are less active and therefore burn less calories.

For the record, my male cat did not put on weight after he was neutered. He has always been slender and a free eater. I have never needed to do portion control. More uncertainty in trying to answer the question in the title.

1. Cat Owner’s Home Veterinary Handbook page 426 of 3rd edition.

P.S. For an unknown reason purebred cats are somehow less likely to develop obesity than moggies according to Dr Bruce Fogle.

A: Neutering Induces Changes in Food Intake, Body Weight, Plasma Insulin and Leptin Concentrations in Normal and Lipoprotein Lipase–Deficient Male Cats.

B: Effects of dietary fat and energy on body weight and composition after gonadectomy in cats.