The Metabolic Impact of Spaying and Neutering

Spaying and neutering are common and beneficial for most pets—they reduce overpopulation and certain health risks. But sterilization also changes metabolism and appetite. Many owners keep feeding the same amount after surgery and are surprised when their pet gains weight. The fix isn't to skip the procedure; it's to adjust how much you feed so your sterilized pet gets the right number of calories for their new metabolic reality.

This article explains the metabolic impact of spaying and neutering and how to feed your pet correctly afterward so they stay at a healthy weight and avoid obesity-related risks.

What Changes After Spaying or Neutering?

1. Lower Energy Requirements

Removing the ovaries (spay) or testes (neuter) removes sex hormones (estrogen, testosterone). These hormones influence:

• Metabolic rate: Sterilized pets often have a lower resting metabolic rate—they burn fewer calories at rest.
• Activity: Some sterilized pets are slightly less active (though this isn't universal).
• Body composition: There can be a tendency to store more fat and maintain less lean mass.

Result: Spayed and neutered pets typically need fewer calories per day than intact pets of the same weight, age, and activity level. Studies and veterinary guidelines often cite a reduction in the roughly 20–30% range (e.g., around 24–30% depending on species and source), though individual variation exists.

2. Appetite Can Increase

At the same time, some sterilized pets show increased appetite—they want to eat more just when their body needs less. If you keep feeding the same amount as before surgery (or more, because they're begging), weight gain is very likely.

So after spay/neuter: need fewer calories, may want more food. Portion control and accurate calorie targets become even more important.

Why This Leads to Weight Gain

• Same portions as before: Pre-surgery portions were right for an intact pet; after surgery they're too many calories.
• Relying on bag feeding guidelines: Those charts don't account for spay/neuter, so they often recommend amounts that are too high for sterilized pets.
• Giving in to begging: Sterilized pets may beg more; feeding extra treats or larger meals pushes them over their new, lower calorie need.
• Not recalculating: Many owners never adjust portions after the procedure, so slow weight gain happens over months or years.

The solution is to recalculate daily calories for your pet as a sterilized adult and feed that amount using the calorie statement on the food.

How Much Less to Feed?

There is no single number that fits every pet, but as a starting point:

• Dogs: Spayed/neutered adults often need roughly 20–30% fewer calories than intact dogs of the same weight and activity (some sources cite around 30%). Breed and size variations exist.
• Cats: Neutered cats are at high risk of weight gain; they often need roughly 20–30% fewer calories than intact cats (some sources cite around 24%). Many adult cat foods are formulated for neutered cats; still, portion control matters.

The best approach is to use a pet calorie calculator that includes spay/neuter status. Our calculator applies a lower energy requirement for sterilized pets so the daily amount we recommend is already adjusted. Then use the calorie statement on the bag or can to convert that into cups or cans per day.

When to Adjust

• Right after surgery: Once your vet clears normal feeding (often within 24–48 hours), switch to portions calculated for a spayed/neutered pet rather than intact. Don't wait until weight gain is obvious.
• If your pet is already overweight: Work with your vet on a safe weight-loss plan; the calorie target will be below maintenance. Our meal planner can give you a target; your vet can confirm it and rule out medical causes of weight gain.
• As they age: Senior sterilized pets may need even fewer calories. Recheck body condition and weight regularly and reduce portions if they're gaining.

Other Ways to Support a Healthy Weight

• Stick to the 10% rule: Treats and extras should be no more than 10% of daily calories so the main diet isn't displaced and calories don't creep up.
• Keep activity up: Encourage play and exercise appropriate for their age and health. Sterilized pets don't have to be couch potatoes—activity helps burn calories and maintain muscle.
• Weigh and assess regularly: Use the scale and BCS every few weeks so you can adjust portions early if they start to gain.

The Bottom Line

Spaying and neutering reduce energy needs (often by about 20–30%) and can increase appetite. Feeding the same amount as before surgery—or following generic bag guidelines—is a major reason sterilized pets become overweight or obese.

To prevent weight gain:

1. Recalculate daily calories for your pet as spayed/neutered (use a calculator that includes this).
2. Portion using the calorie statement on the food.
3. Limit treats to 10% and keep activity consistent.
4. Monitor body condition and weight and adjust as needed.

Our pet meal planner factors in spay/neuter status so you get a daily calorie target that matches your sterilized pet's real needs—helping them stay at a healthy weight for life.