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Our read is that fasting is a well-supported intervention, particularly for metabolic health, but its application should be situational and carefully managed.
The primary goal of intermittent fasting or time-restricted feeding is to extend the duration of unfed states, which can improve autophagy genes and increase mTOR, according to Andrew Huberman and Rhonda Patrick.
While fasting can offer benefits for metabolic health and potentially slow aging, experts like Peter Attia and Paul Saladino caution against chronic or extreme fasting due to risks of muscle loss, hormonal disruption, and other adverse effects.
The best strategy for long life and health involves a combination of proper diet, intermittent fasting, varied exercise, and hormetic stress, as noted by David Sinclair.
Intermittent fasting with a six-hour eating window can improve autophagy genes in the morning and increase mTOR at night, according to Rhonda Patrick and Paul Saladino. Stopping eating at least 3 hours before bed and going to bed slightly hungry improves sleep quality, as noted by Peter Attia and Rhonda Patrick. Andrew Huberman eats according to his desired alertness levels, consuming water and caffeine early in the day and eating his first meal around 11:00 AM or noon.
Intermittent fasting for 2-3 non-consecutive days per week showed minimal benefit on insulin sensitivity, inflammation, or protein turnover in a study of 50 people aged 30-65, according to David Sinclair. Rapid weight loss through extreme fasting or calorie restriction may lead to individuals 'going off the rails' afterward, negating benefits, as noted by Andrew Huberman. Prolonged fasting in individuals with type 1 diabetes carries a risk of developing diabetic ketoacidosis, according to Peter Attia. Peter Attia stopped fasting due to difficulty regaining lean muscle mass, losing approximately 20 lbs of muscle over three years. Chronic fasting or exhaustive exercise can lead to highly elevated baseline cortisol production in animals, as stated by Paul Saladino. Many in the longevity community who advocate extreme fasting or protein restriction may lack lean muscle mass and have compromised hormones, according to Paul Saladino. The prevailing longevity strategy of eating as little as possible and avoiding meat may be misguided; restricting specific amino acids is more effective for extending lifespan, Paul Saladino suggests. Quarterly 7-10 day water-only fasts profoundly reduced hormone levels, including total testosterone, TSH, and negatively impacted thyroid function, as observed by Peter Attia. Intermittent fasting, when not carefully managed for protein intake, can lead to a deterioration of body composition, Peter Attia warns. For men, insufficient sleep, extreme calorie restriction, excessive fasting, very low carbohydrate intake, or using certain drugs can lead to dangerously low testosterone levels, according to Paul Saladino. Short periods of caloric restriction or intermittent fasting are unlikely to provide longevity benefits related to cellular health, autophagy, or clearing senescent cells, as noted by Peter Attia and Andrew Huberman. Fasting can initially increase chemotherapy sensitivity in patients with established tumors but may eventually lead to more aggressive, metastatic, and treatment-resistant tumors, according to Paul Saladino.
Peter Attia would consider resuming long-term fasting if presented with compelling evidence from higher-order models like dog studies. The optimal duration for daily fasting is unknown and may depend on the fasting goal, according to Peter Attia. It is unclear whether GLP-1 agonists and SGLT2 inhibitors cause more lean muscle mass loss than fasting or lifestyle interventions, as noted by Peter Attia. The optimal combination of molecules, exercise, and fasting for individual longevity is not yet fully understood, according to David Sinclair. The translation of observed benefits from calorie reduction in animal studies to tangible benefits in humans is uncertain, as stated by Andrew Huberman. While short-term fasting may offer metabolic benefits, its long-term effects on the gut microbiota are not yet understood, according to Andrew Huberman. It is not clear if a constitutive 30% calorie restriction produces a longevity phenotype in humans or if it would be desirable, as Peter Attia notes. There is no significant difference in outcomes between eating 3000 calories over 12 hours versus 3000 calories over 6 hours, according to Peter Attia. It is unclear whether adding heavy whipping cream to coffee may affect a fasted state, as Peter Attia notes. Combining intermittent fasting (16:8) with a ketogenic diet for muscle gain is not yet scientifically supported, according to Andrew Huberman. Achieving maximal autophagy in humans might require fasting for approximately three days, as noted by Peter Attia, Rhonda Patrick, and Paul Saladino. Intermittent fasting may extend lifespan, although this is still an open question and difficult to study in humans, according to Peter Attia, Andrew Huberman, and David Sinclair.
Mechanistic and trial evidence converge on a real, replicable effect.
Benefits hold across the populations where it's been tested.
Mechanistic and trial evidence converge on a real, replicable effect.
The intervention improves the primary outcome at standard doses in healthy adults.
The effect size is large enough to matter clinically, not just statistically.
The headline effect shrinks once you account for trial quality.
Most of the support comes from short or small studies.
The headline effect shrinks once you account for trial quality.
The headline effect shrinks once you account for trial quality.
Animal-model results don't translate to the human protocol being recommended.