The correlation between weight and health is a lot murkier than media in general, and these shows in particular, represent. It’s much more reliable to measure blood and vitals, such as cholesterol and blood pressure, to establish wellbeing and risk.
Rapid changes in weight tho, in either direction, are well established for having permanent harmful effects. It also tends to make it more difficult to maintain weight loss, and more likely someone actually increases in weight over time.
These shows make it seem like losing weight at any cost is desirable, and don’t put focus on the actually accurate metrics of wellbeing, while ignoring the negative long term impacts of rapid weight loss. It’s a very warped view of health that focuses on an aesthetic feature.