Intermittent fasting is not a diet of “what to eat” but a regimen of “when to eat”: meals are limited to a certain window (for example, 8 hours), and the rest of the time — only water and calorie-free drinks.
The idea is that periods without food switch on the cell's repair mechanisms — autophagy and the energy sensor AMPK — and improve metabolism. But it is important to separate what is proven from what is fashionable.
What is actually proven
In humans, intermittent fasting helps reduce weight and improve a number of metabolic markers (insulin sensitivity, blood pressure, lipids) — largely because people end up eating fewer calories.
The loud promises about longevity and “switching on autophagy by the clock,” however, are not yet proven in humans: most data on life extension come from animals, and there are almost no direct studies of the effect of intermittent fasting on human biological age. For weight, its effectiveness is comparable to ordinary calorie restriction.
Who it suits and cautions
For many healthy people, mild schemes (for example, 12–16 hours without food) are safe and convenient. But intermittent fasting is not for everyone.
Contraindicated, or requiring caution and a doctor's supervision: in pregnancy and breastfeeding, diabetes (especially on insulin or sugar-lowering drugs), eating disorders, in children and adolescents, and at low weight. The main thing is not to overeat during the “window” and not to sacrifice the quality of nutrition for the sake of timing.
Assess your metabolic age
Your eating pattern affects metabolism — assess your metabolic age:
Frequently asked questions
Does intermittent fasting extend life?
There is as yet no direct proof of this in humans — most data on longevity come from animals. In humans, intermittent fasting helps reduce weight and improve metabolic markers, but for this effect it is comparable to ordinary calorie restriction.
How many hours should I fast?
There is no strict “correct” number. Mild schemes of 12–16 hours without food suit many people. Longer fasting windows have no proven health advantages for most people and increase the risk of breakdowns and deficiencies, so chasing numbers is not worthwhile.
Who should not do intermittent fasting?
It should be avoided or used only under a doctor's supervision in pregnancy and breastfeeding, diabetes (especially on insulin), eating disorders, low weight, and in children and adolescents. Healthy people should be careful not to overeat during the eating window.
Related terms
Sources
- NIA (NIH) — Calorie Restriction and Fasting Diets: What Do We Know
- Intermittent fasting: metabolic effects (review). NCBI/PMC
- Caloric restriction and aging epigenetics. NCBI/PMC