What is the impact of crash diets on metabolism?

Crash diets are characterized by severely restricted calorie intake, often leading to rapid weight loss. While the immediate effects might seem advantageous, one significant consequence of these diets is the impact on metabolism.

When the body is subjected to extreme calorie restriction, it adapts by conserving energy to ensure survival. This is often achieved by reducing the metabolic rate, which is primarily influenced by body composition. During crash dieting, along with fat loss, there is frequently a loss of lean body mass, including muscle. Muscle tissue is metabolically active; it burns more calories at rest compared to fat tissue. Therefore, a reduction in muscle mass results in a lower overall metabolic rate, leading to fewer calories being burned throughout the day.

In contrast, the other options do not accurately reflect the physiological responses to crash dieting. Some might suggest that metabolic rates could significantly increase or remain unaffected, but these claims overlook the adaptive responses of the body under caloric stress. Similarly, boosting muscle mass and metabolism would typically require a balanced diet and regular physical activity, rather than deprivation. Thus, the correct answer highlights the detrimental effect of crash diets on metabolic rate through the potential for muscle loss and metabolic slowing.