What is AMPK and how do you activate it (through fasting or exercise)?
Exercise is the most solid way to activate AMPK. Fasting has surprisingly little measurable effect in muscle itself, and a ketogenic diet even lowers AMPK in muscle.
AMPK is an energy sensor found in almost every cell. The moment a cell runs low on energy, AMPK rapidly adjusts more than a hundred processes: sugar and fat metabolism are recalibrated and the cell's self-cleaning process (autophagy) is set in motion. In short, AMPK makes the cell more efficient when resources are scarce.
Exercise is the best-proven way to activate AMPK. Physical exertion creates an immediate energy deficit in the muscle cell, which switches AMPK on straight away. In addition, exercise releases signalling molecules that also activate AMPK in other tissues. Animal studies show that AMPK in the vessel wall can prevent vascular damage, but whether this holds true in humans remains unclear.
Fasting works less powerfully than many people think. Through hormones such as glucagon and adrenaline, AMPK can rise in multiple tissues. However, seven days of fasting had no measurable effect on AMPK activity in human muscle itself (PMID ...). Intermittent fasting protected the blood vessels of mice via AMPK, but those results have not yet been confirmed in humans.
A ketogenic diet actually lowered AMPK levels in skeletal muscle, as a twelve-week randomised study in healthy individuals showed. In terms of AMPK, keto therefore differs fundamentally from exercise or short-term fasting, even though this is rarely stated as clearly in popular media.
The practical value of AMPK lies partly in blood sugar regulation. AMPK directs glucose transporters to the surface of muscle cells, enabling the blood to absorb glucose more efficiently. It also suppresses glucose production by the liver, which is precisely the mechanism by which metformin (a widely used diabetes drug) works. Exercise achieves this reliably; the effects of fasting on muscle AMPK are far less well documented in humans.
Based on multiple human studies, including a randomised trial with a ketogenic diet and a fasting study in muscle, supplemented by mouse animal experiments and review articles. The basic mechanism of AMPK is well established; for specific interventions such as fasting in muscle or a ketogenic diet, the evidence is moderate and sometimes surprisingly contradictory.