Can fasting really rejuvenate your cells?
Fasting has clear cell-rejuvenating effects in animal research, but in humans the evidence is still limited to small studies using biomarkers. The most promising findings have not yet been confirmed in large human studies, so caution is warranted.
In mouse studies, the effects of fasting on cellular rejuvenation are quite impressive. After four days on a fasting-mimicking diet followed by normal food intake, researchers observed more stem cells and progenitor cells in multiple organs, less body fat, a lower risk of cancer, and even the formation of new brain cells in older animals. Bimonthly fasting cycles also extended lifespan in mice. This has been demonstrated consistently and repeatedly in animal research.
Particularly promising is the effect on the nervous system. In aged mice, fasting periods were able to 're-awaken' stem cells that produce myelin (the protective insulating layer around nerves). These cells had lost their ability to respond properly due to age, but recovered this ability after fasting. The drug metformin had a comparable effect. This is interesting in the context of diseases such as MS, but the research has been conducted exclusively in mice.
In the fat and immune tissue of very old mice, intermittent fasting reduced the number of 'exhausted' stem cells, partially restored their function, and improved the immune balance in that tissue. Again, this concerns animal research.
In humans, the evidence is considerably thinner. One small pilot study with three cycles of a fasting-mimicking diet showed improvement in multiple risk biomarkers for cardiovascular disease, diabetes, and cancer, without serious side effects. However, this was an exploratory study, not proof that fasting actually rejuvenates human cells. Time-restricted eating (limiting food intake to a specific window of the day) theoretically has beneficial effects on the mitochondria in blood vessel walls, but this is still based on animal and laboratory research. Proven cognitive or clinical benefits in humans are lacking.
Whether fasting also actively clears 'aged' cells or reverses epigenetic ageing in humans has not yet been sufficiently studied. The idea is biologically plausible and is supported by laboratory and animal research, but robust human studies are not yet available.
Evidence is based on multiple mouse studies (moderate to limited quality), one small human pilot study, and several review and mechanistic articles. No large randomised studies in humans are available.