Your body eats its own garbage: autophagy and fasting

On 3 October 2016 the Nobel Prize in Medicine wasn't shared. It went entirely to one man, the Japanese biologist Yoshinori Ohsumi. For work on yeast. The same yeast that makes bread rise.

In the early '90s, in Tokyo, nobody even knew whether yeast did it. Ohsumi took yeast cells, cut off their food and looked inside them under the microscope. He watched them fill up with bubbles of their own garbage. When a cell runs out of food, it doesn't sit there and die. It picks up a broom.

The name had already been given in 1963 by the Belgian biologist Christian de Duve, and he took it from Greek: autophagy. The cell eats itself. It sounds like a punishment. It's how it stays new. Ohsumi found the genes that make it happen, and the same mechanism runs in your own cells.

The idea

Autophagy is not a switch that flips at 16 hours of fasting. It's a staircase with six steps, and most people stop at the second. It's not only how many hours you don't eat. It's what you do inside them.

The body works in two shifts. When you eat, a sensor inside the cell, mTOR, gives the order: "build, store." As long as it's on, the cleaning waits. When you stop eating, it switches off, and the night shift begins. Breakfast at 7, a snack at 11, something sweet at 11 at night: that's a body living in an endless day.

It builds on rubble.

The staircase, as the idea describes it, has six steps.

Around 12 hours: the inspector. A protein, Beclin-1, walks through every corner of the cell and tags whatever is broken: misfolded proteins, aged mitochondria, broken parts. Nothing is thrown out yet. It's writing the report. The hunger you feel here is mostly habit: ghrelin, the hunger hormone, rings at the hour you ate yesterday, like an alarm clock.

14 to 16 hours: the bag. A membrane wraps the tagged material and seals it in a bubble, the autophagosome. At the same time growth hormone rises, protecting muscle and unlocking stored fat. This is where most people eat. The bag is tied, the garbage truck is on its way, and you cancel the pickup.

17 to 20 hours: recycling. The bag merges with the lysosome, a factory with more than fifty enzymes. Damaged proteins become amino acids again and get reused. It isn't demolition, it's renovation: the house is rebuilt with its own bricks. Neurons, cells that stay with you almost your whole life with no spare parts, are among the first to gain. The brain switches to ketones, and many describe it as a clear, quiet mind.

20 to 24 hours: the power plants. Mitophagy picks out the damaged mitochondria one by one, the ones producing less energy and more wear, and replaces them. Like a fleet of trucks getting rid of its wrecks: you don't have more energy, you have better energy.

24 to 36 hours: the inner guard. Xenophagy hunts down anything foreign that has slipped inside the cell, where the immune system struggles to reach, and stem cells, the body's repair reserve, go through quality control. Hunger here, the idea says, has simply gone.

36 hours and beyond: the watchmaker. Special escorts take damaged proteins one at a time and lead them to the lysosome. The cell is no longer cleaning rooms. It's repairing objects.

The hours are a map, not a clock. In humans autophagy is hard to measure, and most of the timings come from animals and cell cultures.

Exactly when you climb a step, nobody knows. That the mechanism exists and wakes up with hunger is what the Nobel was for.

And here's the most useful part: two people fast for 16 hours and reach different steps. A carb-heavy dinner delays the second step by an hour or two, because the liver empties more slowly. Sitting still delays it further. And if you break the fast with sugar, mTOR switches back on at once, and whatever was halfway stops halfway.

You don't need heroics or 48-hour fasts. You need to give your body a night. Every year you close one cycle. Inside you, thousands close every day, as long as you don't interrupt them.

You don't create the cleaning. You just stop cancelling it.

The practices

1. Twelve hours of night. Twelve hours between the last meal of the day and the first of the next. Every day, at roughly the same time. For example 20:00 to 08:00. It's the first step and the base for everything else.
2. Protein last. The last meal before the fast built around protein (eggs, fish, legumes, meat) with few carbohydrates. Bread, pasta and dessert at night push the second step back by an hour or two.
3. Twenty minutes of movement. Light movement, such as walking, for 20 minutes, somewhere between the 10th and 14th hour of the fast. If you ate at 20:00, that means a morning walk before your first meal.
4. Eggs before bread. Break the fast with eggs or fish, then anything else. Never with sugar, juice or something sweet first.
5. One step up. Once 12 hours feels easy, once or twice a week push your first meal later, so you pass 16 hours and enter the 17–20 range. Not abruptly, and not every day at first.

Politically correct statement of the dayNo fasting beyond 16 hours if you're pregnant, breastfeeding, under 18, have a history of eating disorders, or have diabetes and take medication for blood sugar or blood pressure without your doctor. If you feel dizzy, get palpitations or feel weak, eat and stop there.