Autophagy: your cells' recycling system

Autophagy is one of the most talked-about words in fasting, and one of the most misunderstood. It's real, it's important, and fasting does boost it. But almost everything you'll read about its timing in people, such as "autophagy starts at 16 hours", goes far beyond the evidence. Here is what scientists actually know.

What autophagy is

The word means "self-eating", but it's better thought of as recycling. Inside each of your cells, worn-out parts, misfolded proteins and even invading germs are wrapped in a small bubble and carried to the lysosome, the cell's recycling centre. There they're broken down into building blocks the cell can use again ¹.

What fasting does to it

When nutrients are scarce, cells lean on autophagy to recycle their own material for energy and building blocks. In mice engineered so that autophagy glows under the microscope, starvation increased it in most tissues, though by different amounts in each organ, and some organs ran it busily even with food ². Another mouse study found that a short fast dramatically increased autophagy in brain cells, which had been thought to be protected from it ⁵.

What we know in people

That's roughly where the human evidence stands: encouraging signals from small, short studies that measure markers in blood. We don't yet know how much autophagy increases in your liver, muscles or brain during a 16-hour fast, or whether a 24-hour fast adds much more. Researchers think the benefits of fasting for health and ageing may partly come from autophagy, but that link is still being tested ⁶.

What you can do

• Keep a regular fasting rhythm. Daily fasts give cells repeated periods of low nutrients, the condition that triggers autophagy in experiments ³.
• Exercise. In mice, a single workout switched on autophagy in skeletal and heart muscle, and it may be part of why exercise is so good for metabolism ⁷.
• Let the night do the work. The overnight hours are the easiest part of any fast to keep.
• Ignore products and plans that promise to "maximize autophagy": nobody can measure that outside a laboratory.

Sources

1. Levine B, Kroemer G. Biological Functions of Autophagy Genes: A Disease Perspective. Cell. 2019;176(1-2):11-42. doi.org/10.1016/j.cell.2018.09.048
2. Mizushima N, Yamamoto A, Matsui M, et al. In vivo analysis of autophagy in response to nutrient starvation using transgenic mice expressing a fluorescent autophagosome marker. Mol Biol Cell. 2004;15(3):1101-11. doi.org/10.1091/mbc.e03-09-0704
3. Bagherniya M, Butler AE, Barreto GE, et al. The effect of fasting or calorie restriction on autophagy induction: A review of the literature. Ageing Res Rev. 2018;47:183-197. doi.org/10.1016/j.arr.2018.08.004
4. Jamshed H, Beyl RA, Della Manna DL, et al. Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in Humans. Nutrients. 2019;11(6):1234. doi.org/10.3390/nu11061234
5. Alirezaei M, Kemball CC, Flynn CT, et al. Short-term fasting induces profound neuronal autophagy. Autophagy. 2010;6(6):702-10. doi.org/10.4161/auto.6.6.12376
6. de Cabo R, Mattson MP. Effects of Intermittent Fasting on Health, Aging, and Disease. N Engl J Med. 2019;381(26):2541-2551. doi.org/10.1056/NEJMra1905136
7. He C, Bassik MC, Moresi V, et al. Exercise-induced BCL2-regulated autophagy is required for muscle glucose homeostasis. Nature. 2012;481(7382):511-5. doi.org/10.1038/nature10758