10 peer-reviewed studies on extended fasting — summarized in plain English so you can understand the science without a PhD.
Cell Stem CellNew England Journal of MedicineNature CommunicationsPLOS ONEScience Translational Medicine
Note: We summarize research findings but this isn't medical advice. Consult a healthcare provider before fasting.
Key Researchers in Fasting Science
Dr. Valter Longo
USC Longevity Institute
Pioneer of fasting-mimicking diet research. His work on stem cell regeneration is why we know 72h is the sweet spot.
Dr. Mark Mattson
Johns Hopkins / NIH
Neuroscientist studying fasting and the brain. His NEJM review is the definitive overview of intermittent fasting.
Dr. Yoshinori Ohsumi
Nobel Prize 2016
Won the Nobel Prize for discovering autophagy mechanisms — the cellular cleanup process fasting activates.
All 10 Studies
1
2017Science Translational Medicine
Fasting-mimicking diet and markers/risk factors for aging, diabetes, cancer, and cardiovascular disease
Wei M, Brandhorst S, Shelehchi M, et al.
In plain English: This landmark study from USC tested a fasting-mimicking diet on 100 people. After just 3 monthly cycles, participants saw improvements in markers linked to aging, diabetes, cancer, and heart disease. It's one of the first big human trials showing fasting can actually move the needle on disease risk factors.
Key Findings
✓Reduced body weight, body fat, and waist circumference
✓Lowered blood pressure in people with elevated levels
✓Decreased IGF-1 (linked to aging and cancer risk)
✓Improved markers for diabetes and heart disease risk
✓Benefits were greatest in people who started with elevated risk factors
Fasting-mimicking diet causes hepatic and blood markers changes indicating reduced biological age and disease risk
Brandhorst S, Levine ME, Wei M, et al.
In plain English: This 2024 study found that fasting cycles can actually make your body biologically younger. Using blood markers that predict biological age, researchers found that people doing monthly fasting-mimicking diets reduced their biological age by about 2.5 years. Your birthday stays the same, but your body acts younger.
Key Findings
✓Reduced biological age by ~2.5 years based on blood markers
✓Decreased risk factors for diabetes and cardiovascular disease
✓Lowered liver fat (important for metabolic health)
✓Benefits persisted even after returning to normal eating
Effects of Intermittent Fasting on Health, Aging, and Disease
de Cabo R, Mattson MP
In plain English: This review from the National Institute on Aging (published in one of medicine's top journals) summarizes decades of fasting research. The big takeaway: fasting triggers a 'metabolic switch' from burning sugar to burning fat, and this switch activates powerful cellular repair processes. It's the scientific foundation for why fasting works.
Key Findings
✓Fasting triggers metabolic switching from glucose to ketones
✓Ketones aren't just fuel — they trigger beneficial cellular signaling
✓Improved insulin sensitivity and blood sugar regulation
✓Enhanced brain health and cognitive function
✓Reduced inflammation and oxidative stress
✓2-4 weeks needed for body to adapt to fasting routine
Prolonged Fasting Reduces IGF-1/PKA to Promote Hematopoietic-Stem-Cell-Based Regeneration and Reverse Immunosuppression
Cheng CW, Adams GB, Perin L, et al.
In plain English: This is THE study that put 72-hour fasting on the map. Researchers found that fasting for 2-3 days flips a 'regenerative switch' — it kills off old, damaged immune cells and triggers stem cells to produce brand new ones. It's like rebooting your immune system. This is why 72 hours became the magic number.
Safety, health improvement and well-being during a 4 to 21-day fasting period in an observational study including 1422 subjects
Wilhelmi de Toledo F, Grundler F, Bergouignan A, et al.
In plain English: The largest fasting safety study ever done — 1,422 people fasting for 4-21 days under medical supervision. The results? Fasting was safe, people felt better emotionally and physically, and side effects were minimal. This is the study to cite when someone says 'isn't fasting dangerous?'
Key Findings
✓1,422 subjects completed fasts of 4-21 days safely
✓96% reported improved emotional and physical well-being
✓Weight loss averaged 2-6 kg depending on duration
✓Blood pressure and blood sugar improved
✓Side effects were minor (hunger, headache, fatigue) and temporary
✓No serious adverse events when properly supervised
Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting
Anton SD, Moehl K, Donahoo WT, et al.
In plain English: This paper explains the 'metabolic switch' in plain terms — what happens when your body shifts from burning sugar to burning fat/ketones. The switch typically happens 12-36 hours into a fast. Once flipped, your body enters a state that promotes fat burning, cellular repair, and brain protection.
Key Findings
✓Metabolic switch occurs after 12-36 hours of fasting
2017Journal of the Academy of Nutrition and Dietetics
Intermittent Fasting and Human Metabolic Health
Patterson RE, Sears DD
In plain English: A comprehensive review looking at what intermittent fasting does to human metabolism. The conclusion: fasting improves multiple markers of metabolic health including insulin sensitivity, blood lipids, and inflammation — independent of weight loss. In other words, fasting helps even if the scale doesn't move.
Key Findings
✓Fasting improves insulin sensitivity
✓Reduces markers of inflammation
✓Benefits occur even without significant weight loss
In plain English: A classic study from 1970 that mapped exactly what happens metabolically when humans don't eat. It showed that the body is remarkably good at adapting — switching to fat and ketones for fuel while preserving muscle. This paper is why we know the body doesn't just 'eat muscle' during fasting.
Key Findings
✓Body adapts to fasting by switching to fat/ketone metabolism
✓Brain adapts to use ketones instead of glucose
✓Muscle protein is largely preserved during short fasts
The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers
Harvie MN, Pegington M, Mattson MP, et al.
In plain English: Compared intermittent fasting to regular calorie restriction for weight loss. Both worked for losing weight, but intermittent fasting was better at improving insulin sensitivity and reducing belly fat. This suggests fasting has metabolic benefits beyond just eating less.
Key Findings
✓Intermittent fasting as effective as daily calorie restriction for weight loss
✓Better improvements in insulin sensitivity with fasting
✓Greater reduction in belly fat with fasting approach
Fasting-Mimicking Diet Is Safe and Reshapes Metabolism and Antitumor Immunity in Patients with Cancer
Vernieri C, Fucà G, Ligorio F, et al.
In plain English: Tested fasting in cancer patients receiving chemotherapy. Found it was safe, reduced side effects, and actually boosted the immune system's ability to fight cancer. While more research is needed, this suggests fasting might help cancer treatment work better.
Key Findings
✓Fasting-mimicking diet was safe in cancer patients
✓Reshaped metabolism in ways that may fight cancer
✓Boosted tumor-fighting immune cells (CD8+ T cells)
✓Reduced immunosuppressive cells
✓Patients tolerated fasting well during chemo
✓Suggests fasting may enhance cancer treatment efficacy