Via Ben Azadi

"Overfasting backfires. Human studies show that there's a reduced metabolic rate with chronic fasting, just like chronic caloric restriction. Studies show it actually can make your glucose levels worse because your body starts to break down muscle, produce cortisol, which raises glucose, and then of course you lose lean muscle mass. Fat loss requires contrast, not constant deprivation."

— Scientists Tested Every Fasting Window — This One MELTED the Most Fat, at 10:52

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One of the biggest mistakes people make is thinking of fasting as constant deprivation.

"Fat loss requires contrast, not constant deprivation… just as important as the fast is the proper feast, the refeeding."

The key principle for success is hormesis—a biological phenomenon where a beneficial effect results from exposure to a low dose of an agent that is otherwise toxic or lethal in a higher dose. Fasting is a hormetic stressor, just like exercise. It's beneficial, but only if you allow for recovery.

Constantly fasting without adequate refeeding violates the principle of hormesis. Your body doesn't adapt positively; it goes into survival mode. The solution is to introduce "metabolic flex days" or refeed days.

• Signal of Abundance: A refeed day, with higher calories, healthy carbs, and ample protein, signals to your body that famine is over. This gives your metabolism permission to speed up again.
• Thyroid Support: Refeeding, particularly with healthy carbohydrates, supports thyroid function, which is often suppressed by chronic low-calorie intake.
• Muscle Glycogen Replenishment: Refeeding restores muscle glycogen, improving workout performance and energy levels.
• Psychological Break: A planned refeed day makes the entire process more sustainable and prevents feelings of deprivation that can lead to binge eating.

A couple of notes:

• "Metabolic Flex" does not mean binging: A "refeed" is not a "cheat day." Aim for a controlled increase in nutrients. It's not justification to eat junk or overly-processed food.
• Heavy on Protein and Complex Carbs: A "refeed" that's focused on healthy proteins and complex carbs is far more effective for thyroid and muscle health than one that is high in refined sugars.

By cycling between fasting (stress) and feasting (recovery), you keep your body responsive and prevent metabolic adaptation, ensuring consistent progress.