2016Nobel Prize in Physiology or Medicine
Ohsumi (Nobel Prize)
Yeast genetics
Identified the genes that control autophagy, showing how cells recycle their own parts and why it matters for disease.
Find on PubMed ↗Research library · Recovery & repair
Fasting and autophagy: the clean-up crew
Autophagy is how your cells break down and recycle worn-out parts. Fasting and exercise both switch it on. The science is strong in cells and animals; in humans, timing and benefits are still being worked out.
Early evidence2016Nobel Prize for discovering how autophagy worksYoshinori Ohsumi, Nobel Prize in Medicine
−10–11mmHg blood pressure eating 8am–2pm, with no weight lossSutton 2018, Cell Metabolism (8 men)
16:8eating window alone didn't beat normal meals for weight loss over 12 weeksLowe 2020, JAMA Intern Med, 116 adults
01
The basics
What autophagy is
The word means 'self-eating'. Inside every cell, a membrane wraps around damaged proteins, worn-out mitochondria and other junk to form a bubble called an autophagosome. It then fuses with a lysosome, a sac of digestive enzymes, and the contents are broken down into building blocks the cell can reuse.
Cells turn autophagy up when nutrients are scarce. Low insulin and low amino acids switch off the growth signal mTOR and switch on the energy sensor AMPK, which together start the clean-up. Exercise does something similar in muscle.
In yeast, worms and mice, boosting autophagy extends lifespan and protects against many age-related diseases. In humans we can't yet measure it easily in living tissue, so we don't know exactly how many hours of fasting are needed or how big the benefit is.
How a cell recycles itself
A membrane wraps around damaged parts, seals into a bubble, fuses with a lysosome full of enzymes, and the contents are broken down for reuse.
02
How it works
What happens as a fast goes on
1
0–4 h: Fed
Insulin is high; your body uses and stores the food you just ate.
2
4–16 h: Using stores
Insulin falls and the liver releases stored sugar (glycogen).
3
12–24 h: Fat burning
As glycogen runs low, the body burns more fat and makes ketones.
4
24 h+: Deeper recycling
In animals, autophagy rises clearly. Long fasts need medical advice.
03
Measure it
Can you measure it?
- Not directly. Autophagy can only be measured in tissue samples in research labs.
- Blood ketones (finger-prick meter) show you've switched to fat burning. 0.5 mmol/L or more is nutritional ketosis, which usually takes 16–24 hours of fasting or a very low-carb diet.
- Practical markers of a healthy eating rhythm are steadier energy, better fasting glucose and insulin, and lower blood pressure.
Try your number
Fed / overnightGentle fastKetones risingLong fast: medical advice
072
Simplified. Timing varies with your last meal, activity level and body size.
04
What the research says
The key studies
2018Cell Metabolism
Sutton et al.
8 men with prediabetes
Eating all meals between 8am and 2pm for 5 weeks lowered blood pressure by 10–11 mmHg and improved insulin sensitivity, without weight loss.
Find on PubMed ↗2020JAMA Internal Medicine
Lowe et al. (TREAT)
116 adults
A 16:8 eating window without other changes led to no more weight loss than three normal meals a day, and some of the loss was muscle.
Find on PubMed ↗2022NEJM
Liu et al.
139 adults with obesity
When calories were matched, adding an 8-hour eating window didn't improve weight loss over 12 months.
Find on PubMed ↗2012Nature
He et al.
Mice
Exercise triggered autophagy in muscle, and that autophagy was needed for exercise to improve blood sugar control.
Find on PubMed ↗2019NEJM
de Cabo & Mattson
Review
Intermittent fasting improves several health markers in animals and some human trials, likely through switching between fed and fasted states.
Find on PubMed ↗05
Take action
A sensible way to use fasting
Think of fasting as a rhythm, not a punishment. Food quality and total amount still matter most.
- 1
Start with 12 hours overnight
For example 7pm to 7am. Most people can do this easily.
- 2
Eat earlier rather than later
Finishing dinner 3+ hours before bed helps blood sugar and sleep.
- 3
Try 14–16 hours some days
If it suits you and you feel well, a few days a week.
- 4
Exercise too
Exercise turns on autophagy in muscle and improves the benefits of fasting.
- 5
Protect your muscle
Get enough protein in your eating window, and keep lifting.
- 6
Skip it if...
You're pregnant, under 18, have a history of eating disorders, or take insulin or diabetes pills, unless your doctor agrees.
06
Myth or fact
Common myths, checked
✕ MythAutophagy switches on exactly at 16 hours.
✓ FactThat number comes from social media, not human studies. It rises gradually and depends on many factors.
✕ MythLonger fasts are always better.
✓ FactLong fasts can cost muscle and aren't safe for everyone. Benefits beyond 1–2 days aren't proven in healthy people.
✕ MythFasting is magic for weight loss.
✓ FactIn trials, it works about as well as any other way of eating fewer calories.
✕ MythBlack coffee breaks a fast.
✓ FactBlack coffee, plain tea and water have almost no calories and are fine for most people.
07
Questions
Frequently asked
Does fasting help women differently?
Some women find long fasts affect their cycle, sleep or mood. Gentle 12–14 hour overnight fasts are a safer place to start.
Can I take supplements to boost autophagy?
Spermidine, resveratrol and others raise autophagy in lab studies, but human evidence is thin.
Is a 3-day fast worth it?
There's no strong evidence it helps healthy people, and it carries risks. Only under medical supervision.
08
Sources
References and related topics
- Ohsumi (Nobel Prize) (2016). Nobel Prize in Physiology or Medicine. Yeast genetics. PubMed ↗
- Sutton et al. (2018). Cell Metabolism. 8 men with prediabetes. PubMed ↗
- Lowe et al. (TREAT) (2020). JAMA Internal Medicine. 116 adults. PubMed ↗
- Liu et al. (2022). NEJM. 139 adults with obesity. PubMed ↗
- He et al. (2012). Nature. Mice. PubMed ↗
- de Cabo & Mattson (2019). NEJM. Review. PubMed ↗