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Why Health Experts Are Quitting Fasting (BV #32)
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Why Health Experts Are Quitting Fasting (BV #32)
Jay Feldman Wellness1h 18mSep 3, 2026
Watch the originalSkip daily 16:8 fasting entirely — even 4 days of intermittent fasting measurably shifts cortisol rhythm and suppresses T3 by up to 55% within 24 hours, and Thomas DeLauer's proposed fix (fewer but longer 20–22 hour fasts) produces the same hormonal damage per the studies he himself cites.
Key evidence
- A single day of fasting increases cortisol rhythm amplitude; 4 days shifts the full circadian cortisol curve.
- A 24-hour fast produces a 55% drop in T3, the active thyroid hormone regulating metabolic rate.
- Alternate-day fasting studied beyond 6 months still shows suppressed T3 and disturbed cortisol — no adaptation occurs.
Caveats
- Human autophagy data relies on white blood cell proxy markers; actual whole-body autophagy during fasting is not reliably measurable.
- Fasting does improve metabolic markers in people with obesity or type 2 diabetes, but the panel argues this equals outcomes from simple caloric restriction or weight loss by any method.
Insights
Study finding
Just 4 days of intermittent fasting shifts cortisol rhythm — not years as influencers claim
- Frontiers in Nutrition: even a single fasting day increases cortisol rhythm amplitude
- Endocrinology study: IF powerfully increases cortisol secretion AND alters circadian cortisol timing within days
Study finding
A 24-hour fast drops active thyroid hormone T3 by 55% within that single day
- T3 suppression is adaptive — body lowers metabolic rate when fuel is scarce
- Alternate-day fasting studies lasting 6+ months still show persistently low T3, disproving adaptation claims
Risk warning
Chronic fasting preferentially deposits fat into visceral compartment, worsening metabolic risk
- Cortisol is lipolytic from subcutaneous fat but drives preferential storage into visceral/organ compartments
- Higher HPA axis activity is a key risk factor for metabolically obese normal-weight ('skinny fat') phenotype
Risk warning
Fasting lowers testosterone via increased SHBG and reduced LH pulsatility — not just a cortisol issue
- Starvation signaling downregulates sex steroids: reduces androgens in men, disrupts cycle and progesterone in women
- Sex hormone binding globulin rises during fasting, impairing steroid hormone action at the cellular level
Dietary change
Eating carbohydrates in the morning lowers cortisol more effectively than protein does
- Carbs raise blood glucose and stimulate insulin, which directly opposes cortisol — protein also raises glucagon, sustaining gluconeogenesis
- Morning insulin sensitivity is highest after overnight fast, making carbs especially effective at suppressing stress hormones then
Study finding
Autophagy benefits in humans are largely unproven — animal model findings don't reliably translate
- Human autophagy studies rely on white blood cell proxy markers; direct measurement is too invasive, and data is mixed
- Calorie restriction lifespan extension in rodents was confounded by ad libitum controls having shortened lifespans — not true extension
Study finding
Clearing fatty acid metabolites (ceramides, diglycerides) from muscle and liver reverses insulin resistance regardless of method
- Pancreatic fat clearance alone can put type 2 diabetes into complete remission if beta cells haven't fully declined
- Exercise, caloric restriction, fasting, and medication all improve insulin sensitivity via the same mechanism — removing ectopic lipid
In this video
- 1mintro
- 2mThomas Delauer admits that intermittent fasting increases cortisol
- 10mwhat fasting does to your digestion, thyroid, hormones, and metabolism
- 16mwhy intermittent fasting is stressful and increases cortisol
- 20mThomas Delauer says intermittent fasting every day is harmful
- 28mthe consequences of long-term intermittent fasting
- 32mmore fat-burning doesn’t mean better health
- 36mThomas DeLauer’s new approach to fasting: does it actually make sense?
- 41mshould we try to increase autophagy for better health?
- 46mare longer fasts better than daily intermittent fasting? do they improve insulin sensitivity?
- 53mthe best way to increase autophagy
- 1h 5mwhat to do if fasting makes you feel better
- 1h 15mrestoring health and finding balance after vegan, OMAD, and carnivore diets
Quotes
“If you're frail by the time you get to 50, 60, 70 years old, I don't think the autophagy is going to matter anymore.”
— Mike Fave
“I want to increase like I want to minimize the amount of damaged proteins, let's say. And so I'm going to damage more proteins to try to trigger more autophagy. Like, that's what we're saying here. It's um I think it's just a totally backward way of thinking.”
— Jay Feldman
“Half of my own health problems were self-induced by hooking on to some particular little reductionistic pathway and there's all these benefits and then adjusting my lifestyle to try to optimize things and then getting a negative outcome because I didn't have the full picture.”
— Mike Fave
Flashcards
How quickly does intermittent fasting measurably shift cortisol rhythm, according to the studies cited?reveal
Within 4 days of starting time-restricted feeding.
Why does cortisol rising from fasting not reliably improve body composition?reveal
It releases subcutaneous fat but preferentially deposits it as visceral fat.
What does a 24-hour fast do to T3 levels?reveal
Drops T3 by approximately 55%.
Why is improved fasting insulin during fasting not strong evidence of better insulin sensitivity?reveal
Insulin drops simply because no food is consumed, not because cells respond better.
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