A growing body of research, primarily in animal models, shows that intermittent fasting may be protective for the health of adults and seniors. This form of dietary restriction, where you don't eat for at least 12 hours each day, would for example increase lifespan in mice, and it would protect against cardiovascular diseases and metabolic diseases.
As long as you don't hold on to your hair, intermittent fasting therefore appears to be a good preventative approach to safeguarding one's long-term health. This is why this approach is gaining more and more followers, including among adolescents. However, previous studies were conducted on adults, so it is not yet known whether these same beneficial effects also apply to young people. German researchers from the Helmholtz Zentrum research center in Munich and the Ludwig-Maximilians-Universität Munich have attempted to explore this topic, with worrying results.
The effect of intermittent fasting on metabolism may be different in adolescents
In their study, published on February 25, 2025 in the journal Cell Reports, they studied the effect of intermittent fasting on adolescent (2 months old), adult (8 months old), and senior (18 months old) mice. In each age group, a portion of the mice followed this intermittent fasting for 5 or 10 weeks, to also evaluate the effect of following such a dietary restriction over a long period. Compared to mice without dietary restriction, mice with long-term fasting all lost weight. This was the case only for young mice for short-term fasting, showing a first difference between adolescent mice and adults.
Short-term intermittent fasting had a beneficial effect on metabolism at all ages, notably improving blood sugar (glucose levels) and insulin sensitivity. However, over the long term, this positive effect was observed only in adult mice and not in adolescent girls. This confirms that the impact of intermittent fasting on metabolism varies depending on age.
Intermittent fasting affects pancreatic cell growth in young people
To understand these differences, the authors took a closer look at the function of pancreatic beta cells, which secrete insulin and therefore play a key role in metabolism. Long-term intermittent fasting improved their activity in older mice, but had a negative impact in younger mice. The number of pancreatic islets (which contain insulin-producing beta cells) decreased in these younger mice, as did their insulin content. Intermittent fasting is normally beneficial for beta cells, so we were surprised to find that young mice produced less insulin after long-term intermittent fasting.", declares in a press release Leonardo Matta, first author of the study.
The effect of this fasting is therefore very different between old mice and young mice: in the former, it improves their metabolism, probably by repairing some damage caused by aging; but it was harmful to the metabolism of adolescents, in whom there is not yet any damage to repair. Because one of the effects of intermittent fasting is that it would improve the recycling capacity of cells, helping them to renew themselves. This would be especially important later in life, but not at its beginning, when this process is already working quite well. On the contrary, in young mice, long-term intermittent fasting decreased the proliferation of pancreatic cells, thus causing the opposite effect to that in seniors. During the period of development and maturation, intermittent fasting could disrupt the flow of nutrients and hormonal balance necessary for cell differentiation and organ development., warn the authors.
Cell maturation is disrupted due to intermittent fasting
This decrease in pancreatic cell growth was caused by blocking several genes involved in the maturation of these cells (which was the case only in young mice). This decrease in the activity of certain genes was similar to that observed in people with type 1 diabetes, where the pancreas no longer produces enough insulin to control blood sugar. Our study confirms that intermittent fasting is beneficial for adults, but it could be risky for children and adolescents, concludes Stephan Herzig, director of the study and director of the Institute of Diabetes and Cancer at the Helmholtz Zentrum. The next step will be to explore in more depth the molecular mechanisms behind this observation."
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