Fasting and How It Could Help You Slow Down Aging

by: Noah Grossman

Edited and approved by Stephen C. Rose, PhD

Fasting has been part of human life for centuries, for religious, cultural, and practical reasons. In modern health research, the most-studied approaches are intermittent fasting, alternate-day fasting, and time-restricted eating. These approaches are not magic shortcuts to a longer life, but they have attracted serious scientific interest because they can improve several metabolic risk factors linked to aging and chronic disease.[1,2]

The strongest human evidence so far is not about lifespan itself. Researchers have not yet shown that fasting extends lifespan. What human trials show is that some fasting patterns can help with weight loss, waist circumference, insulin sensitivity, blood pressure, and some blood lipid markers, especially in people with overweight or obesity or at cardiometabolic risk.[1,3,4] That matters because better metabolic health is tightly linked to healthier aging.

What Fasting May Be Doing in the Body

When eating is more widely spaced, insulin levels generally fall and the body shifts toward using stored fuel. That shift appears to affect nutrient-sensing pathways involved in metabolism, stress resistance, and cellular maintenance.[1,4] In animal studies, these changes are associated with improved resilience and longer lifespan. In humans, the evidence is modest and better described as improved risk markers rather than proven life extension.[1,4]

Autophagy, described as a cellular cleanup process, is one of the most commonly cited reasons fasting is discussed in longevity circles. The biology is real, but much of the strongest evidence comes from cell and animal research rather than from direct, long-term human studies.[1,4]  Similar caution should be applied to claims about fasting dramatically increasing growth hormone or resetting the body. These ideas are often simplified beyond what current human evidence can support.

What Human Studies Actually Show

Time-restricted eating is the most practical fasting pattern for many people because it limits the daily eating window without necessarily requiring full-day fasts. A meta-analysis of randomized controlled trials noted that time-restricted eating modestly improved body weight, body mass index, waist circumference, blood pressure, fasting glucose, fasting insulin, and triglycerides compared with usual diets.[3] These effects were not uniform across every study, but the overall direction suggests that time-restricted eating can be a useful option for some adults.

That does not mean it always outperforms standard calorie reduction. In a randomized controlled trial published in the New England Journal of Medicine, adding an 8-hour time window to calorie restriction did not produce greater weight loss than calorie restriction alone over 12 months.[2] In practice, that means fasting may help some people adhere to a lower-calorie pattern, but the timing strategy itself is not automatically superior.

Alternate-day fasting has also shown short-term benefits in adults. In a controlled human study, it improved several cardiometabolic and inflammatory markers in healthy, non-obese adults.[5] Even so, such findings should not be overstated. Short-term changes in lab markers do not prove long-term protection against disease, nor do they prove a longer lifespan.

A Reasonable Way to Think About Longevity

For now, the best evidence-based case for fasting is indirect: some fasting strategies may improve markers tied to cardiometabolic health, and better cardiometabolic health is associated with healthier aging.[1,3,4] That is a meaningful point, but it is different from saying fasting has already been proven to extend human life.

This distinction matters as much of the interest around fasting comes from animal studies and mechanistic theories. Those findings are valuable, but human aging is more complicated. Long-term outcomes depend on total diet quality, sleep, activity, alcohol use, smoking, stress, medical history, and social factors, not just on meal timing.[1,4]

Which Approach Is Most Sustainable?

If someone wants to try fasting, the most realistic place to start is usually a moderate eating window rather than an aggressive multiday fast. Time-restricted eating is easier to study and follow than prolonged fasting, and it has the strongest practical evidence base for everyday adults.[3] A lot of people can handle a 10-hour or 8-hour eating window well when it aligns with daytime eating rather than late-night eating.[1,3]

Extended fasts are a different category. They can produce larger physiologic changes, but they also increase the chance of side effects and are not appropriate for routine self-experimentation in many people.[4] High-quality human outcome data do not well support claims that longer fasts are automatically better.

Risks and Limitations

Fasting is not for everyone. It can be risky for people who are pregnant or breastfeeding, anyone with a current or past eating disorder, people who use insulin or other glucose-lowering medicines, and people with medical conditions that make long gaps between meals unsafe.[1,4] For older adults, maintaining muscle mass, strength, and sufficient  protein intake also matters. A fasting plan that reduces total food quality or total protein intake may work against healthy aging goals.

Adherence is another issue. A 2025 systematic review found that time-restricted eating increased hunger compared with isocaloric control diets in adults with overweight or obesity.[6] That does not mean fasting never works, but it does mean the 'easiest diet ever' narrative is misleading. A plan that leaves someone persistently hungry is less likely to be sustainable.

The Bottom Line

Fasting is a legitimate area of longevity research, but the evidence needs to be delineated carefully. Human studies suggest modest benefits for weight and   several cardiometabolic markers, particularly those with time-restricted eating and other structured fasting approaches.[1,3,5] Evidence that fasting extends human lifespan remains limited, and many of the most dramatic claims still come from animal studies or theory rather than long-term clinical proof.[1,4]

For people who manage it well, fasting can be a the right tool for improving metabolic health that works best when paired with a nutrient-dense diet, adequate protein, exercise, sleep, and common medical sense. If a fasting routine causes fatigue, dizziness, obsessive thinking about food, or worsens day-to-day functioning, it is not the right fit.

References

1. de Cabo, R.; Mattson, M.P. Effects of Intermittent Fasting on Health, Aging, and Disease. N. Engl. J. Med. 2019, 381, 2541-2551.

2. Liu, D.; Huang, Y.; Huang, C.; et al. Calorie Restriction with or without Time-Restricted Eating in Weight Loss. N. Engl. J. Med. 2022, 386, 1495-1504.

3. Sun, X.; et al. Effects of timing and eating duration of time-restricted eating on metabolic outcomes: systematic review and network meta-analysis. BMJ 2026.

4. Longo, V.D.; Di Tano, M.; Mattson, M.P.; Guidi, N. Intermittent and periodic fasting, longevity and disease. Nat. Aging 2021.

5. Stekovic, S.; Hofer, S.J.; Tripolt, N.; et al. Alternate Day Fasting Improves Physiological and Molecular Markers of Aging in Healthy, Non-obese Humans. Cell Metab. 2019. PMID: 31471173.

6. Crispim, C.A.; et al. Time-Restricted Eating Increases Hunger in Adults with Overweight and Obesity: A Systematic Review and Meta-Analysis of Randomized Controlled Studies. Nutr. Res. 2025.