"Normal" is both relative and a social construct - in both reality and the fashion world it has varied over the ages. It was not so long ago that extra weight was viewed as highly attractive, as it denoted class and wealth (e.g. the ability to eat calorie-dense food with frequency). You can see this in art from those time periods, such as with Rubens and Brueghel, who lauded what we would refer to as physical excess. We don't really even have a firm grasp on what body type overall is actually healthiest, as people of course vary in terms of both metabolic rate, strength, and genetic health. "Normal" in this context is a sliding scale of environmental factors, trends, fads, and social cues.
That being said, I think the fashion industry's take on "normal" is pretty unrealistic and unsustainable on a personal level for most people. My perspective tends to view what is healthy and "best" as a personal thing - the weight and fitness level in which a person both feels and performs at an optimal level for their lifestyle and overall health. A happy medium that doesn't require undue maintenance to keep and doesn't endanger a person's health (either via the slings and arrows of being overweight or underweight, as the case may be).