> “dad weight”, you gain weight because you don’t get good sleep after having a kid.

No this is because you've had a baby and don't need to be in good shape to keep or sleep with your partner, so you stop going to the gym, eating well, doing exercise etc. Applies to both sexes.

As a new dad who has put back on some weight, I'd say the biggest reason is not about "keeping my partner" but purely how I rate different things I need to spend my effort, time and energy on. Less time and more stress makes me more likely to make some poor health decision - for example heading out for a walk or a run would help but right now I'm knackered and just want to sit down because it's the first break I've had today. Or order in food because my plan to cook earlier failed due to an unexpected _something_ or just plain comfort eating.

Kids are great, but undeniably add time and stress. Maintaining good healthy habits is not impossible, but it's easier to let them slide.

a lot of that is water weight, I almost always have to average a weeks worth of weight to get a stable reading on the weight changes. I also, gain like +2lbs if I eat a salty meal the night before.