# Fasting

Category: Metabolism

Also known as: intermittent fasting, caloric restriction

Fasting is a stress state that accelerates tissue catabolism, and Ray Peat consistently argued against its practice as a health intervention. Peat explained that after glycogen stores are depleted—typically within 24 hours in a healthy person—the body begins breaking down its…

9 passages · 2 authors · 2017–2025 · Most-cited: [Ray Peat](https://bioenergeticoracle.com/md/voices/ray-peat/index.md)

Canonical page: https://bioenergeticoracle.com/concepts/fasting

## Synthesis

**Fasting** is a stress state that accelerates tissue catabolism, and Ray Peat consistently argued against its practice as a health intervention. Peat explained that after glycogen stores are depleted—typically within 24 hours in a healthy person—the body begins breaking down its own tissues to produce glucose, with **cortisol** rising to mobilize amino acids from muscle and skin. [Source 1] He cited research showing that on a complete water fast, *80% or more of weight loss came from the destruction of muscle and skin*, whereas a very low-calorie diet with adequate minerals shifted loss almost entirely to fat. [Source 1] Peat emphasized that the liver’s detoxification capacity is shut down by fasting, as the sulfation and glucuronidation systems are suppressed, causing **estrogen** to rise. [Source 1]

The nightly fast during sleep already imposes a degenerative stress, which Peat viewed as a model for understanding longer fasts. As blood sugar falls overnight, **free fatty acids** are mobilized, a process that is inefficient, requires more oxygen, and damages mitochondria. [Source 6] Peat noted that bone loss in women occurs primarily at night, with calcium appearing in morning urine, because the body runs out of glycogen and relies on *inefficient fat oxidation*. [Source 6] He contrasted this with the therapeutic use of sugar in the late 19th century, where feeding diabetics large amounts of sucrose interrupted the destructive process of fat oxidation and supported the regeneration of insulin-producing beta cells, which are killed by free fatty acids. [Source 6]

Georgi Dinkov has extended this critique by documenting that intermittent fasting leads to a *2:1 ratio of muscle loss to fat loss*, an outcome even prominent fasting advocates have acknowledged as unacceptable. [Source 4, 5] Dinkov also highlighted human studies showing that a 24–48 hour fast inhibits the enzyme **17,21-lyase**, decreasing androgen synthesis while increasing aldosterone and showing trends toward elevated **cortisol** and **aromatase activity**. [Source 7] He has further argued that the lipolysis triggered by fasting floods cells with free fatty acids that are directly toxic, damaging organs like the kidneys and liver and inhibiting hair follicle growth. [Source 5]

Peat acknowledged that the apparent benefits of caloric restriction in animal studies were confounded by the reduction of specific harmful dietary components. He stated that restricting **PUFA**, **cysteine**, **methionine**, **tryptophan**, and **iron**—rather than calories themselves—was responsible for increased metabolic rate and decreased oxidative damage. [Source 9] He pointed to later research where animals allowed to eat unlimited fat, protein, and carbohydrate, but with heavy metals kept low, lived longer. [Source 2] Dinkov has proposed that **aspirin** may function as a caloric restriction mimetic, replicating the anti-inflammatory and autophagy-related benefits of fasting without the risks of muscle catabolism or elevated stress hormones. [Source 8]

For those recovering from calorie-restricted or intermittent fasting protocols, Peat advised monitoring **temperature** and **pulse rate** as indicators of metabolic recovery, aiming for 37°C and a pulse of 80–85 beats per minute after breakfast. [Source 3] He recommended using small, physiological doses of **T3**—such as 1–4 micrograms per hour or 10 micrograms with a meal—to rapidly relieve symptoms of metabolic suppression. [Source 3] Peat also noted that providing even small amounts of glucose and minerals like sodium, calcium, magnesium, and potassium during low-calorie periods could greatly reduce tissue loss compared to complete fasting. [Source 1]

## People also ask

### How does fasting affect muscle and skin tissue?

Peat argued that after glycogen depletion, the body breaks down its own tissues for glucose, with cortisol rising to mobilize amino acids; he cited research showing over 80% of weight loss on a water fast came from muscle and skin destruction.

### Why does Peat consider overnight sleep a fasting stress?

Peat viewed the nightly fast as degenerative because falling blood sugar mobilizes free fatty acids, which damage mitochondria and require more oxygen, and he noted that bone loss in women occurs primarily at night due to glycogen depletion.

### What does the corpus suggest as a safer alternative to fasting?

Dinkov proposed that aspirin may act as a caloric restriction mimetic, replicating anti-inflammatory and autophagy benefits without muscle catabolism or elevated stress hormones, while Peat advised small glucose and mineral intake to reduce tissue loss.

## Related concepts

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- [Cortisol](https://bioenergeticoracle.com/md/concepts/cortisol/index.md)
- [Eczema](https://bioenergeticoracle.com/md/concepts/eczema/index.md)
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## Cited passages

Passage numbers match the `[Source N]` markers in the synthesis above.

### Source 1 — Jodellefit: Cortisol, Low Testosterone

Ray Peat · Interview · Jun 1, 2019

> ## Fasting and Intermittent Fasting
>
> **Jodelle Fitzwater:** You hear a lot about fasting and intermittent fasting as a way to improve hormones. Do you see fasting as a way to lower cortisol, or is it contributing to the stress response?
>
> **Ray Peat:** In one day of fasting, the body stores several ounces of glucose in the form of glycogen. If you're healthy, you can go up to 24 hours before you are short on glycogen. As the body senses stress, lowering the T3 slows the rate of fuel use. When your glycogen is gone, you have to start using your tissue to make glucose out of your muscles. If your thyroid didn't slow down during this prolonged stress, you would eat your whole body up in just a few days. But since the depressive process turns off metabolism, it slows the rate of degeneration. If you give a little bit of glucose and minerals—sodium, calcium, magnesium, potassium—during the low-calorie period, you can greatly reduce your tissue loss. On a complete water fast for 10 days, they found that 80% or more of the weight loss came from the destruction of muscle and skin. But if they had a 500 or 600 calorie diet with adequate minerals, almost all of the weight loss was in the form of fat loss. So a complete fast is very destructive to the body.

### Source 2 — Ray Peat KMUD: 12-10-13 Aging and Energy Full Interview

Ray Peat · Interview · Jan 25, 2017 · https://www.youtube.com/watch?v=DEdDTAyZuJU

> **Andrew Murray:** Okay. All right, let's just let people know here. You're listening to Ask Your Herb Doctor on KMED Galbraith 91.1 FM and from now until the end of the show at 8 o'clock, you're invited to call in with any questions either related or unrelated perhaps to this month's subject of aging and energy reversal. Dr. Raymond Peat He's a specialist in hormone physiology and the aging process, having studied it for the last 35 years or so. So, yeah, let's just tell people the number again. I guess it's 923-3911. If you live outside the area, the 800 number is 1-800-KMUD-RAD. That's 1-800-568-3723. Okay, so let's perhaps go on then to what you've mentioned about methylation and demethylation and how that occurs, how that affects the gene, how it silences it, how it allows tumors to grow, and how they have just found now in this piece of research that the very presence of this is a very diagnostic indicator for how well the tumor will continue to grow and how switching this off is actually a fairly new approach to cancer therapy. So in terms of the process of methylation and how this happens and how this is also related to that train of thought, a fairly aberrant train of thought perhaps, but that fasting is good for you and going without is actually fairly healthful and if you starve yourself fairly regularly and live on a very meager caloric intake, you'll actually have a greater chance of longevity and it's not actually true, is it?
>
> **Ray Peat:** No, it was definite about 70 years ago. A researcher named Clive McKay, I think it was, showed that restricting the food supply made animals live longer. But later, people restricted the type of food. kept down the heavy metals in their diet alone and let them eat all the fat, protein, and carbohydrate they wanted, and they lived longer.

### Source 3 — Jodellefit: Listener Q&A: Calories, Cortisol, Cellulite, Exercise, Ephedra & More

Ray Peat · Interview · Nov 12, 2019

> ## Calorie Restriction and Thyroid (T3 vs. T4)
>
> **Jodelle Fitzwater:** Tina asks: Does Dr. Peat advise those coming from calorie-restricted eating and intermittent fasting protocols to slowly increase food intake and possibly count calories?
>
> **Ray Peat:** The important thing is to watch your temperature and pulse rate as indicators of how energetic your metabolism is. It's normal for your metabolic rate to go down during the night, but after breakfast, you should pop right up to a working temperature of 37 degrees Celsius (98.6 Fahrenheit) and a pulse rate of more or less 80 or 85 beats per minute.
>
> **Jodelle Fitzwater:** Her second question was: Should we take T4 with T3, or do you advise just taking T3?

### Source 4 — Metabolic Mastery - Danny Roddy & Georgi Dinkov

Georgi Dinkov · Interview · Oct 17, 2022 · https://www.youtube.com/watch?v=PjJv9n5lkgA

> **Georgi Dinkov:** You know, once you see these things promoted on the late night infomercials, then, you know, it's become really a sleazy thing that basically, you know, what is it, pill pushers and, you know, selling it to old people that don't know any better. But as far as mainstream medicine is concerned, even now the big pro-fasting, caloric restriction, metabolic center, such as University of California, San Francisco is probably the most well-known one. The guy who runs the entire department there, there's a recent study, which I also have on the forum. He said that he himself was an intermittent faster and low carb. He said he recommends neither to any of his patients anymore because His own studies show that they lost rapidly lean muscle mass, which is what Ray has always been saying will happen if you're fast. He says, yes, you will lose fat as well, but first you will lose the muscle because it breaks down so much more easily than the fat and also because the body prefers the glucose. So if you don't give the body the glucose, cortisol will rise and it will preferentially destroy your muscles before it does other things as well. So this study confirmed it and the guy said, yeah, as biased doctors are to us, we fully admit that sarcopenia, which is the loss of muscle mass, is a very bad sign and no diet that actually leads to that should ever be recommended on a day-to-day basis.

### Source 5 — Intermittent fasting causes hair loss by increasing lipolysis and fatty acid oxidation

Georgi Dinkov · Article · Apr 18, 2025 · https://haidut.me/?p=2779

> Despite being all the rage these days on social media, intermittent fasting (IF) has now started to attract powerful opponents in the medical community. Several of the largest medical centers doing human research with IF, have published studies showing IF leads to loss of muscle mass (exceeding greatly the lost fat mass), sleep disturbances, mental illness, fertility issues, etc. As a result, several prominent medical doctors have come out with statements against doing IF unless all other options have been exhausted. One of the doctors who made such a statement also said he himself stopped practicing IF and stopped recommending it to his patients. Like all caloric restriction methods, IF is expected to deplete glycogen stores and when that happens the HPA axis activates and the body starts to consume nutrients (fatty acids and glucose) derived from catabolizing living tissue. Catabolizing fat tissue is what the proponents of IF are mostly after, despite virtually all studies to date demonstrating that muscle tissue is also lost during IF, usually in a ratio of 2:1 in “favor” of muscle tissue, which is a horrible outcome. Be that as it may, it looks like the catabolizing of fat tissue, through a process called lipolysis triggered by fasting, thus increasing fatty acid availability to tissues to use as energy through fatty acid oxidation (FAO), is also not a good idea. Virtually all of Ray’s articles have mentioned the detrimental effects of lipolysis/FAO in one context or another, and even medicine recognizes the negative role lipolysis/FAO plays in metabolic conditions such as diabetes. Elevated free fatty acids (whether from lipolysis or high-fat/low-carb diets) are known to be directly toxic to cells and have already been implicated in the damage of organs such as kidneys and liver even in people without chronic conditions such as diabetes. The study below now extends that toxicity/danger to hair follicles as well, demonstrating that the stress of fasting and subsequent cellular fatty acid abundance it triggers harms hair follicles and greatly inhibits the growth of hair. Logically, the study findings would imply that inhibiting lipolysis/FAO may be beneficial for hair growth. Or maybe, just maybe, don’t fast (or otherwise stress yourself) to start with.
>
> [references]

### Source 6 — Jodellefit: Stress and Your Health

Ray Peat · Interview · Apr 27, 2019

> ## Fasting, Sugar, and Metabolism
>
> **Jodelle Fitzwater:** What about intermittent fasting? Is that a beneficial stressor?
>
> **Ray Peat:** Blood sugar normally falls during the hours of darkness. This is compensated by a rise in free fatty acids in the bloodstream. That is the same pattern that happens when you are under stress. When glycogen is depleted, you mobilize free fatty acids to oxidize for energy. This requires more oxygen and is inefficient. When you aren't getting enough oxygen, your body starts turning protein into glucose. Lactic acid rises, which is a sign of stress. Every night, as you mobilize free fatty acids, you go into this stress state, causing damage to mitochondria. Bone loss in women happens primarily at night; the calcium shows up in the morning urine. This degeneration happens because we run out of glycogen. The longer you go without eating, the more you rely on inefficient fat oxidation.
>
> **Jodelle Fitzwater:** You are not a fan of fat burning for energy.
>
> **Ray Peat:** If you look at blood tests, women have about 80 times greater growth hormone than men. This is an effect of estrogen causing chronically high mobilization of free fatty acids. The high growth hormone is a compensation. To the extent you can minimize that, you reduce the chronic degenerative process.

### Source 7 — Fasting/exercise decreases androgens, increases aldosterone (and possibly cortisol/estrogens) in women

Georgi Dinkov · Article · Oct 26, 2022 · https://haidut.me/?p=2023

> I often get criticized that I rely too much on animal studies, so here is a human one that should give the proponents of caloric restriction / fasting a pause. Even a short fast (24-48 hours) resulted in decreased androgen synthesis in women, while increasing aldosterone. In general, fasting seemed to increase levels of precursors such as pregnenolone and progesterone, and depress all other downstream hormones except aldosterone. According to the authors, this effect is due to fasting inhibiting the activity of the enzymes 17,21-lyase, which is the rate-limiting step in the synthesis of androgens. Since estrogens are also part of this pathway, one would expect estrogen levels to decline. However, the study found a tendency of increased aromatase activity (and thus estrogen), though the effects did not reach statistical significance. The same non-significant, but clear, trend for increase was seen for activity of 11b-HSD1, suggesting fasting may increase cortisol as well. In corroboration, exhaustive exercise, which mimics fasting in terms of biochemical effects was also found to decrease intracellular levels of androgens (first link below).
>
> [references]

### Source 8 — Aspirin may replicate the benefits of fasting, while avoiding its risks

Georgi Dinkov · Article · May 9, 2023 · https://haidut.me/?p=2187

> I just made a post about fasting raising risk of early death by about 30%. On the other hand, fasting has been shown to lower biomarkers of inflammation as well as increase autophagy, with at least the former being undeniably beneficial. We already know from other studies that the benefits of fasting are largely due to lower levels of endotoxin (LPS) as well as restriction of intake of specific amino acids such as tryptophan, methionine, cysteine, arginine, glutamate, etc. Thus, if one were to eat food deficient in those nutrients while also keeping the microbiome in check with charcoal, insoluble fiber, antibiotics, etc then one would not need to restrict calories. However, keeping all these rules in mind can get pretty exhausting and invariably people slip on their dietary rules. So, instead of playing Russian roulette with fasting and hoping it won’t lead to an early death, wouldn’t it be be nice if one could get those benefits of fasting but without the risks, while also not restricting calories, specific nutrients, or worrying about the microbiome? The study below presents evidence that taking aspirin daily may be such an all-in-one caloric restriction mimetic (CRM). The daily HED of the mice dose the study experimented with was about 8mg/kg, which means that taking 2 tablets (325mg each) aspirin daily should be able to replicate for most people the design of this study.
>
> [references]

### Source 9 — Ray Peat Email Advice Depository — Post 469

Ray Peat · Email · Mar 17, 2018

> ## Thread 11
>
> **Question:** There seems to be some evidence that caloric restriction is beneficial. I haven't heard you mention anything about it. I was wondering if you think mild calorie restriction is optimal for health? Or beneficial? Or is just eating low pufa what you consider to be optimal, regardless of calorie intake? Thanks!
>
> **Ray Peat:** I’ve occasionally mentioned that the typical calorie restricted diet increases the metabolic rate and decreases oxidative damage by reducing PUFA, cysteine, methionine, tryptophan, and iron, possibly some random toxins. In one of the big nurses studies, someone noticed that those who ate the most lived the longest, i.e., had the highest metabolic rate.

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