Weight gain after sterilization - myth or truth ?

Most is in the title.
Nifty is to be spayed at the end of the month and I’m quietly worrying about her weight.
She’s not particularly thin at the moment and eating about half of recommended kibble amount.

Anyone tried Orijen Fit & Trim ?

Misty didn't change weight after she was spayed, she put on slightly as she couldn't have proper walks for two weeks but after that she was fine. We have just in the last few days put her on Orijen original and she loves it. I'm sure Nifty will be fine x

I’m currently feeding the original but she eats max 100g per day split in 2 feeds
F&T would mean she eats a bit more but it has even more protein. Concerned it might be too much.

I would say more myth than fact.

Spaying is a major operation which requires rest afterwards & that often leads to weight gain. Plus, neutering can calm some dogs down & so they need less food to maintain proper weight.

So, it's actually the need to reassess feed that makes for weight gain, not the operation itself.

Basically what gilly said. A dog or bitch in full swing will burn more energy just being more anxious/horny and hormones etc, when they are calm they won't. Its not that the loss of the sex organs cause them to gain weight, its the fact they tend to not be so fired up, so given ample exercise they should not gain weight.