Final answer:
Yo-yo dieting, or weight-cycling, is concerning because it can damage metabolism and overall health, often resulting from unsustainable fad diets that lead to rapid weight fluctuations and may increase the risk of chronic diseases.
Step-by-step explanation:
The concerns regarding weight-cycling, also known as yo-yo dieting, include that it may harm metabolism and overall health. When individuals engage in yo-yo dieting, they often follow a pattern of losing weight on a fad diet, only to regain it later, potentially leading to metabolic changes that make future weight loss more difficult and adversely affect their health. This cycle can result in a reduced metabolic rate, increased fat storage, and higher risk of chronic diseases. Moreover, fad diets often promote rapid weight loss, targeting specific body parts without necessary exercise or a balanced diet, which makes them unsustainable and potentially harmful in the long run.