February 14, 2025, 11:43 am | Read time: 5 minutes
Intermittent fasting is considered an effective method to improve metabolism and prevent diabetes. It is also often used for weight loss. However, this method may not be equally beneficial for all age groups. At least, a new study provides some indications of this.
In intermittent fasting, also known as interval fasting, regular eating breaks are taken. The length of these breaks depends on the specific form of intermittent fasting. The most common is likely the 16:8 method: You abstain from solid food for 16 hours, but drinking water, tea, and coffee without milk and sugar is allowed. You can eat during the remaining eight hours. During the fasting phase, the sugar metabolism switches to fat metabolism, improving metabolic processes.1 The body also becomes more sensitive to insulin, which can help prevent type 2 diabetes. Additionally, fewer toxic byproducts accumulate in the liver. In summary, intermittent fasting offers many health benefits. With one caveat: Not every age group seems to benefit from this dietary form. A new study shows that teenagers should probably avoid intermittent fasting.
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Overview
Background of the Study
“Intermittent fasting has proven positive effects; it stimulates metabolism and aids in weight loss and heart disease. However, its potential side effects have not been well understood,” says Alexander Bartelt, Else Kröner Fresenius Professor and Chair of Translational Nutritional Medicine at TUM, in a press release.2 The effects on young organisms, in particular, are largely unexplored. Since the pancreas is still developing in teenagers, the question arises whether intermittent fasting affects the maturation of insulin-producing β-cells.
The study therefore examined how intermittent fasting affects glucose metabolism in young, middle-aged, and old mice. Researchers were also interested in whether the duration of intermittent fasting could have different effects.
Studies on Mice
The researchers divided male mice into three age groups: adolescent, adult, and older animals.3 Each group was randomly split again. One part received unrestricted food, while the other part underwent intermittent fasting. Regardless of age, the studies were conducted for four to five weeks or nine to ten weeks. The following methods were used to analyze the metabolic effects:
- Glucose tolerance and insulin tolerance tests to determine blood sugar regulation.
- Examination of isolated pancreatic islets to analyze insulin secretion.
- Single-cell RNA sequencing (scRNA-seq) to identify molecular changes in β-cells.
- Immunofluorescence staining to measure β-cell mass and cell proliferation.
Additionally, the scientists compared the results of the mouse studies with data from human tissue.
Negative Fasting Effects on Young Test Animals
In adult and older mice, after ten weeks, the metabolism responded better to insulin produced by the pancreas. This process regulates blood sugar levels and can prevent type 2 diabetes. However, such positive effects were not observed in adolescent mice. On the contrary, a decline in beta-cell function, the insulin-producing cells of the pancreas, was observed in younger animals. This can lead to diabetes and metabolic disorders. “Intermittent fasting is generally considered beneficial for beta cells. Therefore, we were surprised that young mice produced less insulin after prolonged fasting,” explains Leonardo Matta from the Helmholtz Association Munich and one of the study’s lead authors. This suggests that intermittent fasting might be unhealthy for teenagers.
But what is the reason for the decline in beta cells in adolescent mice? To find out, the researchers mapped the blueprint of the pancreas using single-cell sequencing and found that the beta cells in young animals did not mature. “At some point, the cells of the adolescent mice stopped developing and produced less insulin,” summarizes Peter Weber from the Helmholtz Center Munich, also a lead author of the study. Only animals whose beta cells were mature at the start of the studies were unaffected.
The comparison with human tissue samples then showed that a similarly disturbed cell maturation is prevalent in patients with type 1 diabetes. However, in this type of diabetes, the destruction of beta cells is due to an autoimmune reaction.
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Intermittent Fasting Remains Effective for Adults–Not for Teenagers
These results suggest that intermittent fasting is not without risk for young people or teenagers. The study shows for the first time that long-term adherence to this dietary form can impair β-cell function in adolescents.
It is particularly important that the molecular changes resemble those observed in type 1 diabetes. This could mean that intermittent fasting might increase the risk of β-cell dysfunction in genetically susceptible individuals.
For adults and older people, however, intermittent fasting remains a promising method for improving metabolism and preventing diabetes.
Interpretation of the Study
The study provides new insights into age-dependent effects of intermittent fasting, but it also has some limitations. Firstly, the results are based on mice, whose metabolism cannot be directly translated to humans. Furthermore, only male animals were considered, so gender-specific differences were not accounted for. Therefore, clinical studies are necessary to clearly demonstrate whether intermittent fasting is harmful to teenagers.
The study also shows that the duration of fasting plays a crucial role–a more detailed investigation of the mechanisms is necessary. Additionally, factors such as the effects of intermittent fasting on hormone balance would be significant.