Intermittent Fasting

Intermittent fasting is an eating pattern that cycles between periods of eating and periods of voluntary abstention from food. Rather than specifying which foods to eat, it focuses on when you eat, alternating an eating window with a fasting window. It is an umbrella term that covers several specific approaches, which differ mainly in how long the fasting periods last and how often they occur.

What unites these approaches is the fasting window itself, the stretch of time without calories during which the body shifts from running on recently eaten food to drawing on its own stored energy. As the fast continues, insulin falls, stored carbohydrate is gradually used up, and the body increases its reliance on fat for fuel. The longer and more regular the fasting periods, the more the body spends time in this fasted state.

Common forms include time-restricted eating, where eating is confined to a set window each day such as the 16:8 method, along with longer or less frequent patterns. The right approach depends on the individual, and fasting is best approached as a sustainable routine rather than an endurance test.

Source: de Cabo & Mattson, NEJM (2019)