yes ,but it's not what you say it's how you say it
In terms of health and wellbeing, Yes.
Yes, if they suddenly start putting on weight without a substantial increase in caloric intake then it probably is a medical condition that needs investigating and you should definitely mention it.
I think it is if you are concerned. And are tactful and gentle. I would not want my husband to be overweight and unhealthy. For his sake and for mine. Or to be a smoker. Or have other unhealthy vices like drug addiction or alcoholism. It would be horrible to have to take care of someone who suffers because of unhealthy habits or lifestyle. Horrible for the both of us. So yes it is right and loving too.
Hell yeah - Babe has that dress shrunk or have you got swollen glands?
yes, if you know they are approaching dangerous weight
not a woman if you know whats good for ya.
They deserve to know your honest opinion about them.. So I would.