Extended fasting is powerful, but it’s not harmless. This article covers the most important fasting risks and downsides, backed by physiology, data, and real experience, to help you avoid common mistakes.

Extended fasting temporarily lowers testosterone, but research and real data show it rebounds during refeeding. Here’s how my levels changed across two multi-day water fasts and why fasting may actually support healthier long-term hormone balance.

Extended fasting can dramatically improve blood sugar regulation and insulin sensitivity. Here’s my real Dexcom CGM data and fasting results.

How fast do ketones rise during fasting? In my 7-, 9-, and 10-day water fasts, I tracked how quickly I entered ketosis and what made the biggest difference. Turns out, movement early in the fast helps you reach deep ketosis faster — and burn more fat along the way. Here’s how glucose drops, ketones rise, and why fasting ketosis is totally different from dangerous ketoacidosis.

Fasting activates autophagy — your body’s cellular recycling system. Learn how different fasting lengths boost repair, longevity, and overall health.