Is starvation mode real?

Starvation mode, as commonly understood, is mostly a myth. The concept that reducing caloric intake drastically leads to increased fat storage due to metabolic slowdown (often referred to as "starvation mode") is not supported by evidence. Instead, what occurs are metabolic adaptations.

For example, Dr. Stephanie Compton explains that while the body does adapt to chronic under-fueling, the idea that drastically cutting calories causes an increase in fat mass isn't supported by thermodynamics. This adaptation is more about the body adjusting its energy needs as body weight decreases, not about entering a mode where it stores more fat despite lower calorie intake 1.

Alan Aragon also debunks the idea of starvation mode during weight loss discussions, clarifying that a slower rate of weight loss is healthier for preserving muscle mass while losing body fat 2. Moreover, Danny Matranga notes that metabolic adaptations exist, wherein the body adjusts its non-exercise activity thermogenesis in response to reduced caloric intake, but these do not lead to increased fat storage as commonly feared 3.

In summary, while the body adapts metabolically to calorie reduction, the popular notion of starvation mode leading to increased fat storage during calorie restriction is incorrect.