Why intermittent fasting could be harmful for teens

MUNICH — Intermittent fasting has become one of the most popular eating patterns of the past decade. The practice, which involves cycling between periods of eating and fasting, has been praised for its potential health benefits. But a new mouse model study suggests that age plays a crucial role in how the body responds to fasting — and for young individuals, it might do more harm than good.

A team of German researchers recently discovered that while intermittent fasting improved health markers in older mice, it actually impaired important cellular development in younger ones. Their findings, published in Cell Reports, raise important questions about who should (and shouldn’t) try this trending eating pattern.

Inside our bodies, specialized cells in the pancreas produce insulin, a hormone that helps control blood sugar levels. These cells, called beta cells, are particularly important during youth when the body is still developing. The researchers found that in young mice, long-term intermittent fasting disrupted how these cells grew and functioned.

“Our study confirms that intermittent fasting is beneficial for adults, but it might come with risks for children and teenagers,” says Stephan Herzig, a professor at Technical University of Munich and director of the Institute for Diabetes and Cancer at Helmholtz Munich, in a statement.

The study looked at three groups of mice: young (equivalent to adolescence in humans), middle-aged (adult), and elderly. Each group followed an eating pattern where they fasted for 24 hours, followed by 48 hours of normal eating. The researchers tracked how this affected their bodies over both short periods (5 weeks) and longer periods (10 weeks).

At first, all age groups showed improvements in how their bodies handled sugar, which, of course, is a positive sign. But after extended periods of intermittent fasting, significant differences emerged between age groups. While older and middle-aged mice continued to show benefits, the young mice began showing troubling changes.

The pancreatic cells in young mice became less effective at producing insulin, and they weren’t maturing properly. Even more concerning, these cellular changes resembled patterns typically seen in Type 1 diabetes, a condition that usually develops in childhood or adolescence.

“Intermittent fasting is usually thought to benefit beta cells, so we were surprised to find that young mice produced less insulin after the extended fasting,” explains co-lead author Leonardo Matta, from Helmholtz Munich.

The older mice, however, actually benefited from the extended fasting periods. Their insulin-producing cells worked better, and they showed improved blood sugar control. Middle-aged mice maintained stable function, suggesting that mature bodies handle fasting periods differently than developing ones.

This age-dependent response challenges the common belief that intermittent fasting is suitable for everyone. The research suggests that while mature adults might benefit from this eating pattern, young people could be putting themselves at risk, particularly if they maintain the practice for extended periods.

The findings are especially relevant given how popular intermittent fasting has become among young people looking to manage their weight. While short-term fasting appeared safe across all age groups, the long-term effects on young practitioners could be significant.

“The next step is digging deeper into the molecular mechanisms underlying these observations,” says Herzig. “If we better understand how to promote healthy beta cell development, it will open new avenues for treating diabetes by restoring insulin production.”

Despite the attention they receive from athletes and wellness influencers, popular dietary trends aren’t one-size-fits-all. What works for adults might not be appropriate for growing bodies — all the more reason that understanding these age-related differences becomes increasingly important.