Is intermittent fasting good for longevity?

In animals, intermittent fasting works impressively: mice, but also yeast, worms and fruit flies live longer and stay healthier when they fast periodically. This has been demonstrated in multiple independent studies. But animal research is not human research, and that gap is large here.

In humans, life extension has never been directly demonstrated. There are no large studies showing that people who fast periodically live longer than people who do not. What is reasonably well supported: weight decreases, insulin sensitivity improves, and risk factors for cardiovascular disease are reduced. These effects have been observed in both normal-weight individuals and those with excess weight.

Intermittent fasting also activates a cellular clean-up process called autophagy. In this process, the body clears away damaged proteins and cell components. In animal research, this process protects against age-related diseases such as cancer, Alzheimer's and Parkinson's. Whether it works just as strongly in humans has not yet been sufficiently proven.

One mechanism involved is noteworthy: fasting raises the level of a substance called spermidine, a small molecule that occurs naturally in cells. In multiple model organisms as well as in human volunteers, spermidine rose during fasting and proved to be necessary for the protective effects. Once its production was blocked, those effects disappeared. Note: several authors of this research have financial interests in companies working on related products, which colours the interpretation.

Safety is not a minor issue. Research signals side effects and limitations for specific groups, such as older people and people of certain sexes. Systematic safety research is still lacking. If you start intermittent fasting, be sure to discuss it with your doctor if you take medication, are pregnant, or have a history of disordered eating.