how do you define dieting (and weight-loss dieting)?
Reducing calories and/or portion control with the explicit and main goal of losing weight.

I believe the only "healthy" weight loss is as a *side-effect* of eating better and getting more exercise. Generally rapid weight loss (more than a pound or two a month) is unhealthy and un-sustainable. There's evidence that rapid weight loss is associated with worse measurements of health (blood pressure, risk for cancers, etc.).