It depends what you are interpreting dieting as and Bodybuilding as.
If you mean dieting down to incredibly low bf% such as prepping for a competition, at severely dehydrated states lacking in electrolytes then yes absolutely, I don't need to give a reason for that. if this is done in conjunction with other chemical compounds such as dieuretics and potent fat burners then even more so.
If by dieteting you mean getting lean enough to look good then no it is not unhealthy, the body is designed to be lean and fit, the human requirement is to escape predators and catch pray by out running it, that is our genetic predisposition, it is a modern view that being fat is ok and fit is an obsession.
I don't feel more needs to be said