Total Fasting Preserves Muscle as Calorie Cutting Crushes Metabolism

Joseph Everett - WIL

Conventional calorie restriction slows metabolism and destroys lean tissue by keeping insulin elevated, whereas complete fasting unlocks stored body fat and protects muscle through surges in human growth hormone.

AI-assisted summary of Fasting vs. Eating Less: What's the Difference? (Science of Fasting) — original source. Check the original for full context.

Source published: 2017-06-22

Key ideas

Total fasting triggers fundamentally different hormonal adaptations than caloric restriction, preserving metabolic rate and muscle mass while suppressing chronic hunger. (0:01)
In the 1944 Minnesota Starvation Experiment, high-carbohydrate caloric restriction dropped participants' body temperatures to 95.8°F and slowed metabolism by 40%, whereas Angus Barbieri safely fasted for 382 days without debilitating side effects. (0:01)
Hunger is regulated by circadian spikes in ghrelin rather than continuous escalation, with clinical studies showing overall ghrelin levels dropping over sustained 84-hour fasts. (5:00)
Fasting lowers insulin levels to activate hormone-sensitive lipase, elevating resting energy expenditure and prompting a surge in human growth hormone to spare lean tissue. (6:59)

Detailed notes

## Background Published on YouTube on June 22, 2017, by Joseph Everett on the channel What I've Learned (WIL), this video examines the stark physiological differences between fasting and merely eating less. The accompanying description highlights that transitioning metabolism into ketosis is crucial for healthy fasting and recommends careful preparation, balancing fasting with adequate nutrient intake.

## TL;DR The video contrasts conventional caloric restriction with complete fasting, demonstrating that eating fewer calories traps the body in glucose dependence, suppresses metabolism by up to 40%, and drives relentless hunger and muscle loss. In contrast, total food abstinence lowers insulin, which activates hormone-sensitive lipase to unlock stored body fat via ketosis while increasing resting energy expenditure. Hunger does not continuously intensify during a fast; instead, the hunger hormone ghrelin peaks in learned mealtime waves and progressively decreases across extended fasts. Furthermore, fasting triggers a spike in human growth hormone and maintains elevated leucine levels, which actively protect lean muscle mass from degradation.

## Atmosphere & style The presentation is analytical, revelatory, and methodically paced, unpacking counterintuitive biological principles through stark historical contrasts and peer-reviewed studies. Juxtaposing the grim psychological and physical deterioration of the 1944 Minnesota Starvation Experiment with the effortless, symptom-free fast of Angus Barbieri creates a compelling narrative hook. The tone remains objective and scientifically grounded, using biochemical textbook diagrams and hormonal timelines to deliver a calm, myth-busting reassessment of human starvation and appetite.

## Bulletin - [00:01](https://www.youtube.com/watch?v=APZCfmgzoS0&t=1s) Total fasting triggers fundamentally different hormonal adaptations than caloric restriction, preserving metabolic rate and muscle mass while suppressing chronic hunger. - [00:01](https://www.youtube.com/watch?v=APZCfmgzoS0&t=1s) In the 1944 Minnesota Starvation Experiment, high-carbohydrate caloric restriction dropped participants' body temperatures to 95.8°F and slowed metabolism by 40%, whereas Angus Barbieri safely fasted for 382 days without debilitating side effects. - [05:00](https://www.youtube.com/watch?v=APZCfmgzoS0&t=300s) Hunger is regulated by circadian spikes in ghrelin rather than continuous escalation, with clinical studies showing overall ghrelin levels dropping over sustained 84-hour fasts. - [06:59](https://www.youtube.com/watch?v=APZCfmgzoS0&t=419s) Fasting lowers insulin levels to activate hormone-sensitive lipase, elevating resting energy expenditure and prompting a surge in human growth hormone to spare lean tissue.

## Key takeaways - [00:01](https://www.youtube.com/watch?v=APZCfmgzoS0&t=1s) Caloric restriction with high carbohydrates keeps insulin elevated, suppressing hormone-sensitive lipase and preventing the body from mobilizing stored body fat. - [00:01](https://www.youtube.com/watch?v=APZCfmgzoS0&t=1s) The Minnesota Starvation Experiment demonstrated that semi-starvation leads to severe physical deterioration, including a 50% drop in endurance and intense food-related neuroses. - [00:01](https://www.youtube.com/watch?v=APZCfmgzoS0&t=1s) Angus Barbieri lost 276 pounds over a medically supervised 382-day zero-calorie fast, maintaining his health and keeping the weight off long-term. - [03:00](https://www.youtube.com/watch?v=APZCfmgzoS0&t=180s) Upton Sinclair documented that total abstinence from food eliminates appetite after the first couple of days, whereas light snacking perpetuates constant, ravenous hunger. - [05:00](https://www.youtube.com/watch?v=APZCfmgzoS0&t=300s) Ghrelin levels fluctuate in conditioned circadian waves linked to usual meal times and subside within roughly two hours if food is not consumed. - [05:00](https://www.youtube.com/watch?v=APZCfmgzoS0&t=300s) An 84-hour fasting study at Aarhus University confirmed that overall baseline ghrelin concentrations drop as a fast extends, making later days easier than the onset. - [06:59](https://www.youtube.com/watch?v=APZCfmgzoS0&t=419s) Unlike conventional dieting which causes metabolic rate to drop, resting energy expenditure actually increases during consecutive days of total fasting. - [06:59](https://www.youtube.com/watch?v=APZCfmgzoS0&t=419s) Calorie-restricted diets that do not enter ketosis force the body to cannibalize muscle tissue via gluconeogenesis to maintain required blood glucose. - [10:08](https://www.youtube.com/watch?v=APZCfmgzoS0&t=608s) Human growth hormone spikes significantly after the second day of fasting, acting as a potent protein sparer by mobilizing free fatty acids for cellular energy. - [10:55](https://www.youtube.com/watch?v=APZCfmgzoS0&t=655s) Physical activity accelerates glycogen depletion and fast-tracks entry into ketosis, preventing the muscle loss that can occur during completely sedentary fasts. - [10:55](https://www.youtube.com/watch?v=APZCfmgzoS0&t=655s) Elevated fasting blood concentrations of leucine stimulate muscle protein synthesis independently of carbohydrate-driven insulin spikes.

## Detailed walkthrough ### [00:01](https://www.youtube.com/watch?v=APZCfmgzoS0&t=1s) Minnesota Starvation Experiment vs. Angus Barbieri

To explore the physiological differences between eating less food and eating no food at all, two starkly contrasting real-world scenarios are examined. In 1944, researchers initiated the Minnesota Starvation Experiment to study the physical and psychological toll of caloric restriction, seeking actionable insights to assist starving populations across war-torn Europe following World War II. Thirty-six healthy men—averaging 178 cm (about 5'10") in height and 69.3 kg (153 lbs) in weight—were chosen as subjects. Following a three-month baseline diet of 3,200 calories per day, the men were placed on a six-month semi-starvation regimen of roughly 1,570 calories daily. Because researchers adjusted individual calorie allowances to force a weight loss target of 1.1 kilograms per week, several participants ended up consuming fewer than 1,000 calories per day. Their food consisted almost entirely of high-carbohydrate staples like potatoes, turnips, bread, and macaroni, with virtually no meat or dairy provided.

```mermaid flowchart TD accTitle: Minnesota Experiment vs Angus Barbieri Fast accDescr: Comparison between caloric restriction in the Minnesota experiment and total fasting by Angus Barbieri.

subgraph CR["Caloric Restriction: Minnesota Experiment (1944)"] CR1["1,570 kcal/day (High Carb, Low Protein/Fat)"] --> CR2["Metabolism drops 40% & Body Temp drops to 95.8°F"] CR2 --> CR3["Severe neurosis, extreme hunger, loss of strength"] end

subgraph Fasting["Total Fasting: Angus Barbieri (1965)"] F1["0 kcal/day for 382 Days (Water, Tea, Black Coffee)"] --> F2["Ketosis: Full access to stored body fat"] F2 --> F3["No debilitating hunger; lost 276 lbs safely"] end ```

The physical and psychological decay of these men was swift and extreme. Deprived of sufficient energy, their average body temperature sank to 95.8°F (35.4°C), and complaints of freezing were universal—one participant famously reported having to put on a sweater on a bright, sunny July day. Physical endurance plummeted by 50%, while overall muscular strength fell by 21%. Mentally, the men grew entirely consumed by thoughts of food, suffering unrelenting hunger and developing strange neurotic rituals, including the obsessive hoarding of cookware, utensils, and recipe books. Some chewed up to 40 packs of gum a day until access was banned, and two men were ejected from the study for scavenging through garbage cans and stealing raw turnips.

By contrast, in 1965, a Scottish man named Angus Barbieri undertook a medical fast lasting over 380 days, ingesting no calories whatsoever—surviving strictly on water, black coffee, and plain tea for over a year. Barbieri successfully dropped 276 pounds, going from 456 pounds down to 180 pounds, and kept nearly all the weight off over the subsequent years, stabilizing around 196 pounds. As reported in a 1973 case evaluation published by the Dundee University Department of Medicine:

> “...the patient remained symptom-free, felt well and walked about normally,” and “Prolonged fasting in this patient had no ill-effects.”

While not a direct one-to-one comparison—given that Barbieri was an isolated case with massive excess body fat—this contrast highlights the starkly diverging hormonal responses triggered by fasting versus caloric reduction. Summarizing this divergence, Dr. Jason Fung, a Toronto nephrologist and author of *The Obesity Code*, observes that compared to total fasting, standard calorie reduction produces less weight loss, more lean muscle loss, and significantly greater hunger.

- **Minnesota Baseline Diet:** 3,200 calories per day for 3 months. - **Minnesota Restriction Diet:** ~1,570 calories per day for 6 months (some men dropped below 1,000 cal/day to hit the 1.1 kg/week loss target). - **Physical Deterioration in Minnesota Subjects:** 50% decrease in endurance, 21% decrease in strength, and body temperature dropped to 95.8°F (35.4°C). - **Angus Barbieri Fasting Record:** 382 days with zero caloric intake, going from 456 lbs to 180 lbs.

---

[03:00](https://www.youtube.com/watch?v=APZCfmgzoS0&t=180s) Upton Sinclair and the Paradox of Hunger

The counterintuitive relationship between food abstinence and appetite was documented more than a century ago by Upton Sinclair in his 1911 work *The Fasting Cure*. Reflecting on his own initial fasts, Sinclair chronicled how ravenous desire for food quickly evaporated rather than building indefinitely:

> “I was very hungry for the first day-the unwholesome, ravening sort of hunger that all dyspeptics know. I had a little hunger the second morning, and thereafter, to my great astonishment, no hunger whatever-no more interest in food than if I had ever known the taste of it.”

Sinclair strongly advocated for sustained fasts of around 12 days, warning against partial measures or intermittent small bites. Addressing inquiries regarding whether eating tiny snacks or taking short 2-to-3-day breaks was easier, Sinclair argued:

> “...perhaps, it might be a good thing to eat very lightly of fruit, instead of taking an absolute fast-the only trouble is that I cannot do it. Again and again I have tried, but always with the same result: the light meals are just enough to keep me ravenously hungry...”

In Sinclair's observations, total cessation of food switches appetite signals off, whereas modest morsels of fruit merely re-trigger cravings and physical weakness. He maintained that a fast naturally concludes when genuine physiological hunger finally returns. He cited numerous letters from readers who completed 10-to-28-day fasts, including a 72-year-old man whose appetite only reawakened after 28 days of zero food, at which point he broke his fast with small amounts of grape juice, tomatoes, and vegetable broth. This lived experience disproves the popular belief that humans become progressively more famished with each passing hour of food deprivation.

---

[05:00](https://www.youtube.com/watch?v=APZCfmgzoS0&t=300s) Ghrelin and the Waves of Appetite

The biological explanation for why hunger fades over prolonged fasting lies in the behavioral pattern of ghrelin, the body’s primary appetite-stimulating hormone. Far from rising continuously when food is withheld, ghrelin fluctuates in learned circadian waves aligned with a person's habitual meal times.

```mermaid flowchart LR accTitle: Ghrelin Hormone Fluctuation During a Fast accDescr: How ghrelin levels rise with habitual meal times and then drop spontaneously.

A["Habitual Meal Time (Lunch/Dinner)"] --> B["Ghrelin Spikes (Hunger Rises)"] B --> C{"Food Ingested?"} C -- "No (Patience)" --> D["Spontaneous Ghrelin Drop after ~2 hours"] C -- "Yes" --> E["Hunger Suppressed by Eating"] D --> F["Overall Baseline Ghrelin Decreases Over Days"] ```

In an experiment conducted at the Medical University of Vienna, patients were evaluated over a 33-hour fast, with ghrelin measured every 20 minutes. The findings revealed that ghrelin levels were at their lowest point at 9:00 AM—the precise moment subjects had gone the longest without food since the previous evening. Ghrelin repeatedly spiked around lunch and dinner times due to conditioned anticipation, but if no food was provided, the hormone spontaneously subsided within two hours. This rhythm explains why busy individuals or professionals can get swept up in work through the lunch hour and completely forget about food until dinner.

Evidence of hunger attenuation over longer spans is supported by clinical research from Aarhus University Hospital in Denmark: - **Study Cohort:** 33 subjects fasted continuously for 84 hours. - **Ghrelin Trajectory:** While diurnal baseline ripples remained, total ghrelin concentrations progressively dropped over the 84-hour window. - **Subjective Experience:** Patients were demonstrably less hungry the longer they refrained from eating, directly aligning with Sinclair’s reports and personal multi-day fasting experiences where day 4 proved dramatically easier than days 1 or 2.

---

[06:59](https://www.youtube.com/watch?v=APZCfmgzoS0&t=419s) Ketosis, Insulin, and Metabolic Adaptation

The underlying driver determining whether an individual feels vibrant or exhausted during a diet is ketosis—the physiological switch from utilizing glucose to utilizing fatty acids and ketone bodies for cellular fuel. Ketosis typically occurs when carbohydrate intake falls below 50 grams per day, combined with moderate protein consumption. A classic ketogenic macronutrient breakdown consists of roughly 75% healthy fats, 25% protein, and 5% carbohydrates, though fasting achieves ketosis much faster by simply depriving the body of all incoming substrate.

```mermaid flowchart TD accTitle: Metabolic pathways of Caloric Restriction vs Fasting accDescr: The role of insulin, hormone sensitive lipase, metabolism, and muscle preservation.

subgraph PathA["Caloric Restriction (Minnesota Style)"] A1["Carbohydrates Ingested"] --> A2["Insulin Elevated"] A2 --> A3["Hormone Sensitive Lipase Inhibited"] A3 --> A4["Body Fat Trapped / Inaccessible"] A4 --> A5["Metabolic Rate Drops (-40%)"] A4 --> A6["Gluconeogenesis Breaks Down Muscle"] end

subgraph PathB["Complete Fasting"] B1["Zero Food Intake"] --> B2["Insulin Plummets"] B2 --> B3["Hormone Sensitive Lipase Unlocked"] B3 --> B4["Abundant Fuel from Body Fat (Ketosis)"] B4 --> B5["Resting Energy Expenditure (REE) Increases"] B4 --> B6["Human Growth Hormone Spikes (Protects Muscle)"] end ```

The primary flaw of the Minnesota Starvation Experiment was that its carbohydrate-rich rations kept the subjects out of ketosis. By feeding them bread, turnips, and macaroni, their bodies were trapped running on glucose. Consuming carbohydrates stimulates the pancreas to release insulin, and elevated insulin directly suppresses hormone-sensitive lipase (HSL)—the critical enzyme required to mobilize stored adipose tissue into free fatty acids. Denied both sufficient dietary fuel and access to their own massive internal fat reserves, their bodies were forced into survival triage:

As Dr. Jason Fung explains regarding resting energy expenditure during a multi-day fast:

> “If you don't do anything about your insulin and just reduce your calories, your metabolism goes down. But what happens during fasting? Well, here's a study of 4 consecutive days of fasting. What happens to your REE - this is this middle line here, that's the resting energy expenditure. It doesn't go down, it goes up. You're burning more energy than you did.”

When insulin remains elevated under calorie restriction, the body cannibalizes functional muscle tissue through gluconeogenesis to produce glucose, producing weakness and muscle atrophy. Fasting bypasses this destructive cycle: insulin levels drop, hormone-sensitive lipase mobilizes abundant body fat, metabolic output goes up rather than down, and the body secretes Human Growth Hormone (HGH) to shield lean muscle mass from degradation.

[10:08](https://www.youtube.com/watch?v=APZCfmgzoS0&t=608s) Human Growth Hormone and the Science of Protein Sparing

As its name suggests, human growth hormone (HGH) is an anabolic hormone that promotes bodily growth. To demonstrate its potent growth-inducing effects, *Lehninger Principles of Biochemistry* highlights an experiment where injecting the human growth hormone gene into a mouse caused it to grow to an unusually large size. Beyond general growth, however, HGH serves an essential survival function during prolonged food deprivation by safeguarding existing lean tissue.

Quoting directly from *Guyton and Hall Textbook of Medical Physiology*, Joseph Everett highlights the physiological mechanism at play: “...growth hormone also mobilizes large quantities of free fatty acids from the adipose tissue, and these in turn are used to supply most of the energy for the body cells, thus acting as a potent 'protein sparer.'” By unlocking adipose stores to fuel cellular energy demands, the elevation of growth hormone directly shields skeletal muscle from catabolism. Clinical data reinforces this protective timeline: in the previously cited study evaluating subjects undergoing an 84-hour fast, human growth hormone concentrations rose significantly after the second day without food.

```mermaid flowchart TD accTitle: Hormonal Muscle Sparing Mechanism During Fasting accDescr: Diagram showing how fasting elevates growth hormone, mobilizes fat, and spares lean muscle tissue.

subgraph FastingState["Extended Fasting (Day 2+)"] HGH["Spike in Human Growth Hormone (HGH)"] end

subgraph EnergyMobilization["Energy Shift"] Adipose["Adipose Tissue Release"] FFA["Free Fatty Acids Mobilized"] end

subgraph TissueProtection["Outcome"] CellEnergy["Cells Fueled by Fatty Acids"] Sparing["Lean Muscle Spared from Breakdown"] end

HGH --> Adipose Adipose --> FFA FFA --> CellEnergy CellEnergy --> Sparing ```

[10:55](https://www.youtube.com/watch?v=APZCfmgzoS0&t=655s) Ketosis, Leucine, and Tim Ferriss’s Fasting Protocol

Entering ketosis typically occurs within the first three days of a fast, though the exact timeline varies based on pre-fast dietary habits and daily physical activity. Ketosis provides a clear biological signal that the body has successfully transitioned to running on stored body fat. The critical connection between activity, ketosis, and muscle preservation is vividly illustrated in Tim Ferriss’s book *Tools of Titans*. During Ferriss’s first clinically supervised seven-day fast, strict facility liability rules barred him from leaving or exercising. Because exercise is an essential catalyst for depleting liver glycogen stores and stimulating growth hormone, this total sedentariness delayed ketosis and led to disastrous body composition changes: Ferriss lost 12 pounds of muscle over those seven days. Conversely, when he adopted a self-directed protocol designed to force rapid entry into ketosis—incorporating activities such as four hours of brisk walking—he completed a ten-day fast and reportedly lost zero muscle mass.

Muscle preservation during ketosis is further reinforced by elevated fasting levels of blood leucine. Leucine is a vital branched-chain amino acid (BCAA) that exerts strong anabolic effects on the body, helping to retain lean mass even in the absence of caloric intake. While lifters often worry that fasting or ketogenic states will hinder muscle preservation because insulin and carbohydrates are traditionally viewed as prerequisites for protein synthesis, leucine independently acts as a potent molecular trigger for muscle protein synthesis. Summing up the cumulative evidence, fasting demonstrates distinct biological advantages over traditional hypocaloric restriction: individuals lose more weight specifically from fat, retain more lean muscle mass, sustain higher energy levels, and suffer far less from persistent hunger. Everett pulls these threads together to deliver a stark conclusion on weight loss dogma: “If proper weight loss is your goal, it might be better to eat nothing at all rather than eating a conventional low calorie diet.”

- **Tim Ferriss's sedentary clinical fast**: 7 days of total physical inactivity caused a loss of 12 pounds of muscle tissue. - **Tim Ferriss's accelerated ketosis fast**: A 10-day fast combining low carbohydrate availability with 4 hours of brisk walking resulted in zero lost muscle mass. - **Leucine's anabolic role**: Higher baseline blood concentrations of leucine during ketosis stimulate protein synthesis pathways without requiring carbohydrate-driven insulin spikes. - **Core physiological advantages of fasting over calorie restriction**: Preferential fat loss, muscle sparing, elevated resting energy expenditure, and reduced appetite.

## Notable quotes > [10:55](https://www.youtube.com/watch?v=APZCfmgzoS0&t=655s) If proper weight loss is your goal, it might be better to eat nothing at all rather than eating a conventional low calorie diet. — Joseph Everett

## Mentioned Aarhus University Hospital, Angus Barbieri, Blinkist, Dr. Jason Fung, Dundee University Department of Medicine, Guyton and Hall Textbook of Medical Physiology, Joseph Everett, Lehninger Principles of Biochemistry, Medical University of Vienna, Minnesota Starvation Experiment, The Complete Guide to Fasting, The Fasting Cure, The Obesity Code, Tim Ferriss, Tools of Titans, Upton Sinclair

## Video description This is about the drastic physiological differences between fasting and eating less

▲Patreon: https://www.patreon.com/WILearned ▲Twitter: https://twitter.com/jeverettlearned ▲IG: https://www.instagram.com/jeverett.whativelearned/

*NOTE* One of the key things in being able to fast in a healthy matter is entering the state of ketosis - that is, switching your metabolism from burning carbohydrate to burning fat. *Considering most people have been burning carbohydrate their whole lives* this can make fasting a challenge. Upton Sinclair recommends doing quite long fasts - 12 days, but you may want to work your way up to longer fasts. Unless you are relatively keto adapted (or have experience with fasting of course), it's important that you take precautions while doing a fast. Fasting isn't inherently dangerous, *but diving into fasting when your body is in no way geared for it can be.* I recommend doing more research before doing longer fasts. "The Complete Guide to Fasting" (http://amzn.to/2tQjxXa) is a good book to start with. As Tim Ferriss puts it: Please don't do anything stupid and kill yourself. It would make us both quite unhappy.

Just in case I should also say that of course you need to balance fasting with eating - You need to survive off of something. I have been doing intermittent fasting the past year (22 hours fasted, 2 hours eating - you can widen it to 16/8, which still provides great benefits) and will fast for a couple days every other month or so. Several other people have recommend a routine like this - Tim Ferriss recommends doing a 3 day fast once per month and a 7 day fast once per year. Also make sure you're getting enough fat, protein, micronutrients and fiber to maintain a healthy weight and healthy body - *excessive* fasting can be very dangerous.

Books Mentioned: "The Obesity Code" by Dr. Jason Fung - http://amzn.to/2rXtalh "The Fasting Cure" by Upton Sinclair - (If you google the title you can find the full book online) "Tools of Titans" by Tim Ferriss - http://amzn.to/2rX6P7E

[BLINKIST] Blinkist is an app I've been using lately to discover new books and review the ones I've already read. It gives you the key points in text or audio form from tons of different non-fiction books. Since I'm always going through so many books to get these done, it's very useful to get me exposed to more concepts beforehand to know if it's worth my time to buy and read through that particular book. Check it out here: http://bit.ly/2sbegMN

For business inquiries: joseph.everett.wil@gmail.com

[Source](https://www.youtube.com/watch?v=APZCfmgzoS0)

中文简报

完全断食能保留肌肉，而节食削减热量却会重创代谢传统的热量限制会因胰岛素维持在高位而减缓代谢并破坏瘦体重，而完全断食则能释放体内储存的脂肪，并通过激增的生长激素保护肌肉。该视频对比了传统热量限制与完全断食，指出减少热量摄入会将身体困在葡萄糖依赖中，使代谢率最高下降40%，并导致持续的饥饿感和肌肉流失。相比之下，完全断食会降低胰岛素水平，从而激活激素敏感性脂肪酶，通过生酮作用释放储存的体脂，同时提高静息能量消耗。断食期间饥饿感并不会持续增强；相反，饥饿素仅在习惯性进餐时间呈规律性峰值出现，并在长期断食中逐渐下降。此外，断食还会引发人体生长激素激增并维持较高的亮氨酸水平，从而积极保护瘦肌肉群免受分解。完全断食会引发与单纯限制热量截然不同的激素适应，在保留代谢率和肌肉量的同时抑制慢性饥饿感。 (0:01) 在1944年的明尼苏达饥饿实验中，高碳水化合物的热量限制使受试者的体温降至95.8°F，代谢减缓了40%，而安格斯·巴比里（Angus Barbieri）安全断食382天，且未出现衰弱性副作用。 (0:01) 饥饿感是由饥饿素的昼夜节律峰值调节的，而非持续递增；临床研究表明，在持续84小时的断食中，饥饿素的总体水平呈下降趋势。 (5:00) 断食能降低胰岛素水平以激活激素敏感性脂肪酶，提高静息能量消耗，并促使人体生长激素激增以保护瘦组织。 (6:59)

Reading summary

Joseph Everett argues that complete fasting triggers distinct hormonal adaptations that conventional caloric restriction fails to activate, enabling the body to access stored fat, preserve lean muscle, and suppress appetite rather than lowering resting metabolism. Metabolic Divergence: Caloric Restriction Versus Fasting (0:01) The physiological divergence between reducing calories and abstaining from food entirely is demonstrated by comparing the 1944 Minnesota Starvation Experiment with Angus Barbieri's 1965 medical fast. In the Minnesota study, 36 men consumed roughly 1,570 daily calories of high-carbohydrate staples, requiring some to drop below 1,000 calories to meet target weight losses. Consequently, subjects suffered a 40% drop in metabolic rate, a 50% decrease in endurance, a 21% reduction in strength, body temperatures sinking to 95.8°F (35.4°C), and severe psychological obsessions with food. In contrast, Barbieri consumed zero calories for 382 days—subsisting on water, tea, and black coffee—and safely lost 276 pounds. A 1973 Dundee University evaluation reported that Barbieri walked normally, remained symptom-free, and experienced no ill effects. Toronto nephrologist Dr. Jason Fung explains that traditional caloric reduction maintains sufficient carbohydrate intake to keep insulin elevated. Chronic insulin presence inhibits hormone-sensitive lipase (HSL), the enzyme required to release stored body fat. Blocked from accessing internal adipose reserves, the body relies on gluconeogenesis to break down lean muscle tissue for glucose while depressing resting energy expenditure. Complete fasting, conversely, drives insulin down, activates HSL to liberate fat stores, and increases resting energy expenditure over consecutive fasting days. The Ghrelin Wave and Diminishing Hunger (5:00) Popular assumptions suggest appetite compounds continuously without food, but clinical and historical evidence indicates hunger diminishes during extended fasts. Author Upton Sinclair noted in his 1911 work, 'The Fasting Cure', that intense cravings vanished after the initial day of fasting, whereas light fruit snacks provoked unrelenting hunger. Sinclair observed that complete cessation of food silenced appetite signals until genuine physiological hunger returned weeks later. Endocrinological research attributes this phenomenon to the diurnal rhythms of ghrelin, the primary appetite-stimulating hormone. A Medical University of Vienna study monitoring subjects over a 33-hour fast revealed that ghrelin reached its lowest point at 9:00 AM, despite subjects having abstained from food since the previous evening. While ghrelin spiked near habitual lunch and dinner hours, levels subsided spontaneously within two hours if no food was consumed. Furthermore, clinical trials from Aarhus University Hospital examining 33 subjects during an 84-hour fast demonstrated that baseline ghrelin concentrations progressively declined across multi-day fasts, making later fasting days subjectively easier than initial ones. Muscle Sparing via Ketosis, HGH, and Leucine (10:08) Extended fasting shifts fuel consumption to fatty acids and ketone bodies, triggering hormonal mechanisms that preserve skeletal muscle mass. According to the 'Guyton and Hall Textbook of Medical Physiology', human growth hormone (HGH) mobilizes large quantities of free fatty acids from adipose tissue to meet cellular energy demands, serving as a potent protein sparer. Data from the Aarhus University Hospital study confirms that HGH concentrations climb significantly following the second day of food deprivation, shielding lean muscle tissue from catabolism. Muscle preservation is further assisted by elevated baseline concentrations of leucine, a branched-chain amino acid that stimulates muscle protein synthesis pathways during ketosis without requiring carbohydrate-driven insulin spikes. Physical activity plays a critical role in unlocking these adaptations quickly. As documented in Tim Ferriss's 'Tools of Titans', a sedentary, clinically supervised seven-day fast delayed ketosis and caused 12 pounds of muscle loss. Conversely, when Ferriss incorporated four hours of brisk walking to rapidly deplete liver glycogen and accelerate ketosis, he completed a ten-day fast with zero reported muscle loss. Everett concludes that total fasting provides distinct advantages over conventional caloric restriction for weight loss by accelerating fat mobilization, protecting lean muscle mass, and naturally blunting appetite. However, the source acknowledges that extreme fasts like Barbieri's rely on substantial initial adipose stores, and successful lean mass retention depends heavily on accelerating ketosis through physical activity.

精炼阅读摘要

Joseph Everett 论证指出，“少吃”与“不吃”在人体内引发的生化反应存在根本差异：传统的低卡路里高碳水节食会使胰岛素持续处于高位，从而锁定脂肪储备并大幅压低代谢率；而完全断食能够打破这一限制，通过触发酮症、升高生长激素与调控胃生长素，实现更彻底的脂肪动员与瘦体重保留。节食与断食的真实极端案例对照 (0:01) 在1944年的明尼苏达饥饿实验中，36名健康男性在经历每日3200卡路里的基线期后，被置于每日约1570卡路里的半饥饿饮食中长达六个月，部分受试者为达到每周减重1.1公斤的硬性指标，摄入量甚至被压低至1000卡路里以下。由于食物主要由土豆、芜菁、面包和通心粉等高碳水化合物组成，缺乏肉类与乳制品，受试者的平均体温骤降至35.4°C（95.8°F），耐力下降50%，肌力减退21%，基础代谢率下跌40%，并表现出严重的神经官能症、翻垃圾桶找食物以及对食谱器具的病态痴迷。与之形成鲜明对比的是1965年苏格兰男子 Angus Barbieri 的长期断食记录。他在医疗监护下持续完全断食382天，仅依靠水、黑咖啡和茶维持生命，体重从456磅减至180磅，并在后续数年中稳定在196磅左右。邓迪大学医学部1973年的评估报告显示，Barbieri 在断食期间完全没有不良症状，行动自如且健康良好。多伦多肾脏病学家 Jason Fung 博士据此指出，相较于彻底断食，常规的节食少吃往往导致更少的减重幅度、更多的瘦肌肉流失，以及显著更强烈的饥饿折磨。胃生长素规律与饥饿感消退悖论 (3:00) 早在1911年，Upton Sinclair 在《断食疗法》（The Fasting Cure）中便记录了禁食期间食欲反直觉消失的现象。Sinclair 观察到，猛烈的饥饿感通常只在断食第一天发作，次日晨起便大幅减轻，随后食欲近乎完全泯灭；相反，若在断食期进食少量水果等微量食物，反而会持续诱发无法遏制的饥饿与身体虚弱。多位经历10至28天断食者的信件也印证了这一现象，真正的生理性饥饿往往在禁食数周后才会再度出现。现代内分泌学为该现象提供了生理依据。维也纳医科大学对33小时断食受试者的监测显示，人体主要的促食欲激素胃生长素（Ghrelin）并非随断食时间无限攀升，而是呈现与习惯性进餐时间吻合的节律性脉冲；在禁食时间最长的早晨9点，其浓度反而处于全天最低谷。即便在就餐时间出现峰值，只要不进食，该激素也会在约两小时内自发回落。丹麦奥胡斯大学医院对33名受试者进行的84小时连续断食研究更进一步证实，随着断食天数增加，胃生长素的总体基线水平逐步走低，受试者主观体验到的饥饿感随时间推移显著减弱。胰岛素阈值与代谢率的分歧机制 (6:59) 区分节食衰竭与断食供能的核心枢纽在于酮症（Ketosis）的启动。明尼苏达实验的核心缺陷在于其供给的高碳水配餐使受试者胰岛素水平居高不下，而胰岛素会直接抑制激素敏感性脂肪酶（HSL）的活性，彻底锁死脂肪组织向游离脂肪酸的转化。受试者既得不到足够的外源能量，又无法动用自身储存的巨量内源脂肪，迫使机体进入极端的生存避险状态：基础代谢率被动下调40%，同时通过糖异生途径加速分解自身肌肉以获取葡萄糖，引发全身无力与严寒感。完全断食则彻底阻断了外源碳水化合物摄入，导致体内胰岛素骤降，促使激素敏感性脂肪酶被全面激活，人体迅速转为分解脂肪生成脂肪酸和酮体来供应能量。Jason Fung 博士引用的4天连续断食数据显示，断食非但不会像常规低卡路里饮食那样导致代谢崩溃，人体的静息能量消耗（REE）反而呈现上升趋势。这意味着只要胰岛素下降并解锁体内脂肪储备，机体便拥有充足的能量流以维持乃至提升代谢运转。生长激素跃升与蛋白质节约效应 (10:08) 针对断食会严重损耗瘦体重的疑虑，内分泌学研究揭示了断食特有的“蛋白质节约”（Protein Sparing）生理防线。《盖顿与霍尔医学生理学教科书》指出，断食期间激增的人体生长激素（HGH）能够大规模调动脂肪组织释放游离脂肪酸，使其成为细胞的主要燃料，从而发挥保护肌肉蛋白质的关键作用。在奥胡斯大学医院的84小时断食研究中，受试者体内的生长激素浓度在无食物摄入的第二天后出现显著飙升。与此同时，酮症状态下血液中的亮氨酸（Leucine）浓度上升，能够直接在分子层面独立激活肌肉蛋白质合成途径，打破了肌肉保护必须依赖碳水化合物与胰岛素的传统设想。然而，能否迅速进入酮症直接影响着肌肉保护的效果。Tim Ferriss 在《巨人的工具》中记载，他在首次7天临床断食中因完全卧床缺乏活动，糖原耗竭滞后导致酮症延迟出现，最终流失了12磅肌肉；但在随后的10天断食协议中，他通过包括4小时快走在内的活动加速耗尽肝糖原储备，迅速诱导酮症启动，实现了零肌肉流失。这表明促进糖原耗竭与尽早建立脂肪供能，是断食过程中保护瘦体重的关键前提。 Joseph Everett 总结认为，相较于限制热量但保留碳水的传统节食方案，完全断食能够更好地避开高胰岛素带来的代谢降级、肌肉消耗与持续饥饿，在减脂效率与维持瘦体重方面具有独特的生理优势。然而，如 Angus Barbieri 的长期断食属于依赖巨量初始脂肪储备并在医疗监护下的极端个案，断食期间进入酮症的速度也受身体活动水平的直接制约，普通人在实践相关方案时必须考量个体代谢耐受与具体的协议设计。

Detailed notes — zh

## Background 该视频由 Joseph Everett 于 2017 年 6 月 22 日发布在 YouTube 频道「What I've Learned（WIL）」上。视频简介指出，本期内容深入探讨了彻底断食（Fasting）与单纯少吃节食（Eating Less）之间巨大的生理机制差异，并强调了进入生酮状态、平衡断食与营养摄入以及循序渐进的重要性。 ## TL;DR 视频通过对比 1944 年明尼苏达饥饿实验与安格斯·巴比里长达 380 天的断食奇迹，系统剖析了节食与断食对人体的截然不同影响。传统低热量高碳水节食会持续刺激胰岛素分泌，锁死脂肪分解通道，迫使身体大幅降低 40% 的基础代谢率并分解肌肉供能，伴随剧烈而折磨的饥饿感。相反，完全断食能让胰岛素降至低谷，促使身体迅速进入生酮状态以体脂为主要燃料，且伴随饥饿素基线下降、生长激素（HGH）与亮氨酸升高，在维持甚至提升代谢率的同时强力保护瘦体重。主讲人结合医学文献与阿普顿·辛克莱、蒂姆·费里斯等人的实践指出，如果以减脂和健康为目标，在科学规划的前提下彻底断食往往远优于传统的低热量少吃节食。 ## Atmosphere & style 整部视频散发着严谨、理智而又颠覆常识的科普魅力，叙事条理清晰、层层递进。主讲人以客观沉稳的口吻穿梭于经典的生理学实验与生动的个人案例之间，用数据图表与权威医学著作不断打破公众对“饥饿”与“挨饿”的固有成见。观看时既能感受到历史实验中节食带来的压抑与折磨，又能在逐步揭开内分泌与代谢保护机制的过程中体会到豁然开朗的智性快感。 ## Bulletin - [00:01](https://www.youtube.com/watch?v=APZCfmgzoS0&t=1s) 1944年明尼苏达饥饿实验表明，摄入高碳水低热量饮食会导致基础代谢率暴跌40%、体温降至35.4°C，且引发极度的心理异化与肌肉流失；而苏格兰男子安格斯·巴比里断食超过380天，不仅减重276磅且全程无不良反应。 - [03:00](https://www.youtube.com/watch?v=APZCfmgzoS0&t=180s) 饥饿素（Ghrelin）并非随断食时间延长而单调攀升，而是在习惯餐点呈波浪式阵发并在约2小时后自发消退；丹麦奥胡斯大学研究证实，断食时间越久，体内饥饿素的整体基线水平反而逐渐降低。 - [06:59](https://www.youtube.com/watch?v=APZCfmgzoS0&t=419s) 低热量高碳水节食会持续刺激胰岛素分泌，从而抑制激素敏感性脂肪酶（HSL）动员体脂，迫使机体分解肌肉通过糖异生供能；完全断食则使胰岛素降至极低，促成酮症并使静息能量消耗（REE）不降反升。 - [10:08](https://www.youtube.com/watch?v=APZCfmgzoS0&t=608s) 在彻底断食的第2天起，人体内的人类生长激素（HGH）与支链氨基酸亮氨酸水平会显著激增，作为“蛋白质节约机制”调动游离脂肪酸供能并直接保留骨骼肌。 ## Key takeaways - [00:01](https://www.youtube.com/watch?v=APZCfmgzoS0&t=1s) 明尼苏达饥饿实验证明，单纯削减热量但保留碳水化合物会导致体能耐力腰斩、肌肉力量下降21%，并伴随严重的食物强迫症与畏寒反应。 - [01:50](https://www.youtube.com/watch?v=APZCfmgzoS0&t=110s) 安格斯·巴比里在医护监测下断食超过380天减重276磅，不仅未出现严苛饥饿感，且长期随访未见健康受损或严重体重反弹。 - [03:00](https://www.youtube.com/watch?v=APZCfmgzoS0&t=180s) 阿普顿·辛克莱早于1911年发现长断食的最大痛苦集中在前两三天，进食微量餐食反而会持续刺激令人无法忍受的贪婪饥饿感。 - [04:30](https://www.youtube.com/watch?v=APZCfmgzoS0&t=270s) 维也纳医科大学内分泌研究显示，饥饿素水平在清晨9点处于全天最低谷，其餐点峰值会在空腹约2小时后自动退去。 - [05:55](https://www.youtube.com/watch?v=APZCfmgzoS0&t=355s) 奥胡斯大学84小时断食实验揭示，受试者的饥饿素基线随断食天数推进逐渐下降，解释了断食第3至4天后饥饿感大幅消退的生理机制。 - [06:59](https://www.youtube.com/watch?v=APZCfmgzoS0&t=419s) 诱发酮症需停止进食或将每日碳水摄入压低至50克以下，从而将身体代谢引擎从葡萄糖完全切换为燃烧体脂。 - [08:00](https://www.youtube.com/watch?v=APZCfmgzoS0&t=480s) 低卡节食因碳水刺激胰腺分泌胰岛素，进而直接抑制激素敏感性脂肪酶（HSL），导致体脂无法动员而被锁死在脂肪库中。 - [08:45](https://www.youtube.com/watch?v=APZCfmgzoS0&t=525s) 热量限制而胰岛素未降低时机体代谢率大幅下降；杰森·冯医生指出，连续断食4天不仅不降代谢，反而促使静息能量消耗（REE）上升。 - [09:30](https://www.youtube.com/watch?v=APZCfmgzoS0&t=570s) 节食状态下身体因无法调取脂肪，被迫通过糖异生分解骨骼肌转化为葡萄糖维持血糖，导致显著的瘦体重流失。 - [10:08](https://www.youtube.com/watch?v=APZCfmgzoS0&t=608s) 《盖顿与霍尔医学生理学》指出，断食期间飙升的生长激素能调动巨量游离脂肪酸供能，充当强效的“蛋白质节约剂”以保护骨骼肌。 - [10:55](https://www.youtube.com/watch?v=APZCfmgzoS0&t=655s) 蒂姆·费里斯的经验表明断食期间切忌静卧不动，缺乏运动不仅推迟进入生酮状态，更会导致严重肌肉流失，而配合步行可加速入酮并保全瘦体重。 - [11:56](https://www.youtube.com/watch?v=APZCfmgzoS0&t=716s) 进入深层生酮后空腹血液中亮氨酸浓度升高，即使在缺乏高胰岛素的情况下也能独立激活蛋白质合成通路，颠覆力量训练必须依赖碳水的误区。 - [12:25](https://www.youtube.com/watch?v=APZCfmgzoS0&t=745s) 相较于引发乏力、代谢减速与肌肉流失的传统节食，彻底断食展现出更高的减脂效率、更好的瘦体重保留以及更持久充沛的精力水平。 ## Detailed walkthrough ### [00:01](https://www.youtube.com/watch?v=APZCfmgzoS0&t=1s) 明尼苏达饥饿实验与安格斯·巴比里的断食奇迹节食（少吃）与断食（完全不吃）在生理上究竟有何不同？为了说明二者的巨大反差，视频引入了两个极具代表性的历史案例。1944 年，为了解热量限制对人体的影响并为二战后饥荒援助提供科学依据，研究人员开展了著名的“明尼苏达饥饿实验”（Minnesota Starvation Experiment）。该实验挑选了 36 名身体健康的年轻男性，平均身高 178 厘米，平均体重 69.3 千克。在最初的 3 个月里，他们每天摄入 3200 卡路里以确立基线；紧接着的 6 个月，摄入量被骤降至平均每天仅 1570 卡路里，甚至为了实现让受试者每周减重 1.1 千克的目标，部分人每日摄入不足 1000 卡路里。更关键的是，他们所吃的全都是高碳水化合物食物，如土豆、芜菁（芜菁甘蓝）、面包和通心粉，肉类和奶制品极少提供。在长达 6 个月的严苛节食下，受试者经历了灾难性的生理与心理摧残。所有人无时无刻不在抱怨寒冷，甚至有人在 7 月艳阳高照的天气里还要穿厚毛衣，受试者的平均体温下降到了 35.4 摄氏度（95.8 华氏度）。他们的体能耐力直接被腰斩，肌肉力量衰退了 21%，更可怕的是精神异化：男人们对除食物以外的一切事物失去了所有兴趣，满脑子全是对食物的病态痴迷，饱受持续而强烈的饥饿折磨。有人出现了收集菜谱和餐具等神经症行为，甚至有两名参与者因偷吃生芜菁和从垃圾桶里翻找剩饭而被逐出实验。起初允许咀嚼的口香糖也因为有人每天嚼掉多达 40 包而被叫停。反观另一个极端案例——1965 年苏格兰男子安格斯·巴比里（Angus Barbieri）的故事。为了治疗严重肥胖，他连续断食超过 380 天，在一年多的时间里完全不进食任何固体食物，仅靠水、黑咖啡和清茶维生。最终他的体重从 456 磅（约 207 千克）降至 180 磅（约 82 千克），足足减掉了 276 磅。根据邓迪大学医学院 1973 年发表的病例报告： > “The patient remained symptom-free, felt well and walked about normally,” and “Prolonged fasting in this patient had no ill-effects.”（该患者没有任何症状，感觉良好且能正常行走，且长期的断食对该患者没有产生不良影响。）令人惊讶的是，安格斯在断食期间从未抱怨过令人抓狂的剧烈饥饿，并且在断食结束后的数年里，体重稳定维持在 196 磅左右，并未反弹。尽管这只是一个个案，且起始体重与明尼苏达实验的健康受试者不可同日而语，但这鲜明地揭示了断食与单纯热量限制带来的生理机能反应存在着天壤之别。正如多伦多肾病专家、《肥胖代码》（The Obesity Code）作者杰森·冯医生（Dr. Jason Fung）所总结的，相比于断食，单纯的热量削减反而会导致：更少的体重减轻、更多的瘦体重流失（即肌肉流失）以及更加折磨人的饥饿感。 - 明尼苏达饥饿实验基线：36 名健康男性，前 3 个月每日 3200 卡，后 6 个月每日约 1570 卡（高碳水低蛋白脂肪）。 - 节食生理代价：耐力下降 50%，肌力下降 21%，体温降至 35.4°C，精神过度聚焦于食物甚至引发病态行为。 - 安格斯·巴比里个案：断食 380 余天，仅饮水、黑咖啡与茶，减重 276 磅，且全程感觉良好无严重饥饿感。 --- ### [03:00](https://www.youtube.com/watch?v=APZCfmgzoS0&t=180s) 饥饿感的悖论：从阿普顿·辛克莱的经验到饥饿素的潮汐节律关于饥饿的常识直觉往往是“不吃东西的时间越长，人就会越饿”，但无论是历史记录还是现代内分泌学，都推翻了这一认知。早在 1911 年，阿普顿·辛克莱（Upton Sinclair）在《断食疗法》（The Fasting Cure）一书中就记录了自己利用断食改善健康的经历。他回忆自己最初尝试断食时的状态： > “I was very hungry for the first day-the unwholesome, ravening sort of hunger that all dyspeptics know. I had a little hunger the second morning, and thereafter, to my great astonishment, no hunger whatever-no more interest in food than if I had ever known the taste of it.”（第一天我非常饥饿，那种所有消化不良患者都熟知的病态、贪婪的饥饿感；第二天早上我有一点饿，但在此之后，令我大为吃惊的是，饥饿感彻底消失了——我对食物失去了兴趣，仿佛从未尝过食物的滋味一样。）辛克莱主张进行 12 天左右的长断食。在回应那些询问是否可以通过“极少量进食水果”或“每隔两三天少吃一点”来代替彻底断食时，辛克莱明确指出断食最大的痛苦都集中在前两三天，而少量进食只会让事情变得百倍艰难： > “Again and again I have tried, but always with the same result: the light meals are just enough to keep me ravenously hungry...” （我一次又一次地尝试，但结果总是相同：微薄的餐食恰恰足以让我保持极度饥饿……）辛克莱甚至提到，断食的真正终止信号是饥饿感的“再次归来”。他援引了一位 72 岁老人的来信，信中说自己在断食 28 天后饥饿感才重新出现，这时才用葡萄汁、番茄和蔬菜汤循序渐进地复食。来信的所有读者都至少断食了 10 天，且无一例外都是等到饥饿感重新浮现才结束断食。日常生活中大多数人也感受过这种悖论：早晨刚醒来时，往往是整整一夜未进食、空腹时间最长的时刻，但许多人清晨却完全不饿，反而到了平时的午餐或晚餐时段饿得前胸贴后背。维也纳医科大学的一项研究利用内分泌监测揭示了背后的机制。研究人员让受试者进行 33 小时的断食，并每隔 20 分钟测量一次其体内的“饥饿荷尔蒙”——饥饿素（Ghrelin）水平。数据显示，受试者的饥饿素水平在早晨 9:00 处于全天最低谷（正是断食时间最长的节点）。更重要的是，饥饿素并不是随着时间持续单调爬升，而是呈波浪式阵发：它精准地在人体习惯的午餐和晚餐时间迎来波峰，仿佛身体在按生物钟等待进食；然而，即使完全不进食，这些饥饿素峰值也会在 2 小时后自发消退。主讲人结合自己做企业咨询顾问时的亲身经历印证了这一点：有时午餐时间到了感觉很饿，但因为工作太忙无暇顾及，硬挺过去后，不知不觉就完全忘记了进食这件事，直到晚餐前都毫无饥饿感。丹麦奥胡斯大学医院（Aarhus University Hospital）的一项涉及 33 名受试者、长达 84 小时的断食实验进一步证实，随着断食天数延长，受试者的饥饿素昼夜节律依然存在，但总体基线水平却在逐日下降。换句话说，断食越久，人实际上变得越不饿。这完美印证了辛克莱的观察和主讲人自身进行 4 至 6 天断食的体悟——第四天往往是整段断食中饥饿感最微弱的一天。 - 饥饿常识误区：不进食饥饿感会无限叠加（错误）；饥饿感以波浪形式出现并会自发退去（正确）。 - 维也纳医科大学 33 小时研究：饥饿素在早晨 9:00 最低；午餐与晚餐时段随条件反射升高，若不进食约 2 小时后自动回落。 - 奥胡斯大学 84 小时研究：随着断食时间推进，饥饿素总体水平随天数逐渐走低，证实“长断食第 3 天后饥饿感消退”的真实生理基础。 --- ### [06:59](https://www.youtube.com/watch?v=APZCfmgzoS0&t=419s) 生理机制的岔路口：酮症、代谢率与肌肉分解 ```mermaid flowchart TD accTitle: Caloric Restriction vs Complete Fasting Pathways accDescr: A flow diagram showing how low-calorie diets cause metabolic slowdown while complete fasting activates ketosis and elevates metabolism. subgraph CR["低热量高碳水节食 (如明尼苏达实验)"] A["摄入少量碳水化合物"] --> B["刺激胰腺持续分泌胰岛素"] B --> C["抑制激素敏感性脂肪酶 (HSL)"] C --> D["无法动用自身体脂 (阻断酮症)"] D --> E["代谢率暴跌 (-40%)、畏寒乏力"] D --> F["糖异生分解宝贵的肌肉供能"] end subgraph FAST["完全断食 (如安格斯·巴比里)"] G["完全停止进食"] --> H["胰岛素降至极低水平"] H --> I["激素敏感性脂肪酶激活"] I --> J["体脂全力分解，进入酮症状态"] J --> K["静息能量消耗 (REE) 代谢率上升"] J --> L["生长激素保护肌肉，极少消耗瘦体重"] end ``` 彻底断食与低卡节食之所以会产生如此巨大的体感差异，其深层生理开关在于“酮症”（Ketosis）。酮症是一种代谢状态，标志着身体的主要能量来源从葡萄糖切换为体内脂肪。除了减脂，它还能大幅提升身体与大脑的运转效率。要诱发酮症，通常需要将碳水化合物摄入压低到 50 克以下且限制过量蛋白质（生酮饮食推荐热量构成为 5% 碳水、25% 蛋白质、75% 优质脂肪）；而进入酮症最简单直接的方式，就是停止进食足够长的时间。明尼苏达饥饿实验的致命死穴恰恰在于此：受试者摄入的微薄热量全部来自土豆、面包等纯碳水，这部分碳水化合物“刚好足以将他们卡在酮症之外”，迫使其代谢引擎持续维持在燃烧葡萄糖的模式上。然而，外部摄入的微量糖分根本无法满足机体需求，身体又因为胰岛素的存在而无法解锁库存的脂肪库。碳水化合物刺激胰腺分泌胰岛素，而高水平的胰岛素会直接抑制“激素敏感性脂肪酶”（Hormone-Sensitive Lipase, HSL）的活性，阻断脂肪动员和分解。因此，受试者空有成堆的脂肪却无法调取，整个人如同坐拥金山却活活饿死，这也解释了为什么他们会极度虚弱、肌肉无力且畏寒怕冷。当身体既无法获得充足外部热量、又无法动用脂肪自救时，它别无选择，只能采取两项自杀式防御措施：第一，全面调低基础代谢率以节省能量。在明尼苏达实验中，受试者的代谢率暴跌了 40%。讽刺的是，如果在完全断食的状态下，人体代谢反而会上升。引用杰森·冯医生的原话： > "If you don't do anything about your insulin and just reduce your calories, your metabolism goes down. But what happens during fasting? Well, here's a study of 4 consecutive days of fasting. What happens to your REE - this is this middle line here, that's the resting energy expenditure. It doesn't go down, it goes up. You're burning more energy than you did."（如果你不对胰岛素采取任何干预，而仅仅是减少热量摄入，你的新陈代谢就会下降。但在断食期间会发生什么呢？这是一项连续断食 4 天的研究。你的 REE——也就是中间这条线，代表静息能量消耗——发生了什么变化？它并没有下降，反而上升了。你消耗的能量比之前还要多。）第二，在缺乏脂肪供能通道时，身体不得不通过糖异生（Gluconeogenesis）分解骨骼肌等瘦体重，将其转化为葡萄糖应付急需。身体本能上极不情愿破坏肌肉，但在无法调用脂肪且必须维持血糖的极端困境下，节食迫使身体蚕食自身肌肉组织。这就是为何少吃节食造成的肌肉流失远比完全断食更为严重的原因——在纯粹的断食状态下，不仅胰岛素骤降激活了巨量体脂燃烧，体内的人类生长激素（HGH）还会随之飙升，全力保护肌肉免受损耗。 - 生酮切换阈值：每日碳水化合物限制在 50g 以下或彻底断食，让胰岛素水平骤降以激活激素敏感性脂肪酶（HSL）。 - 节食代谢惩罚：明尼苏达实验受试者基础代谢率狂降 40%；而在连续 4 天彻底断食的研究中，人体的静息能量消耗（REE）不降反升。 - 肌肉损耗机理：节食因持续刺激胰岛素导致脂肪锁定，被迫通过糖异生大量消耗肌肉转化为葡萄糖；彻底断食则促使生长激素（HGH）激增并以酮体供能，起到肌肉保护作用。 ### [10:08](https://www.youtube.com/watch?v=APZCfmgzoS0&t=608s) 生长激素与断食期间的肌肉保护机制人体生长激素（Human Growth Hormone，简称 HGH）顾名思义是一种强效的合成代谢激素，专门促进机体组织的生长与修复。在经典生物化学教材《雷宁格生物化学原理》（Lehninger Principles of Biochemistry）中曾记载过一个著名实验：当科研人员将人类生长激素基因注入小鼠体内后，这只小鼠的体型长得异乎寻常地庞大。在面临热量极度匮乏的断食状态下，生长激素展现出了另一项至关重要的生理功能——充当肌肉组织的“护盾”，阻止蛋白质分解。这种保护机制在医学界早有详尽的生理学定论。《盖顿与霍尔医学生理学》（Guyton and Hall Textbook of Medical Physiology）中明确阐述了其运作机理：“...growth hormone also mobilizes large quantities of free fatty acids from the adipose tissue, and these in turn are used to supply most of the energy for the body cells, thus acting as a potent "protein sparer."” 换言之，生长激素能调动脂肪组织释放海量游离脂肪酸供细胞维持日常运转，从而使肌肉蛋白免遭消耗。前文提及的那项针对受试者进行84小时断食的研究也证明，从断食的第二天开始，人体内的生长激素水平便会出现显著飙升，为身体保全瘦体重提供坚实保障。 ```mermaid flowchart TD accTitle: 断食状态下的生长激素与肌肉保护机制 accDescr: 展示断食进入第二天后生长激素升高并调动脂肪酸供能以保护肌肉的生理通路 subgraph FastingState["深层断食（第2天起）"] A["生长激素 (HGH) 显著飙升"] B["脂肪组织动员"] C["释放大量游离脂肪酸"] D["细胞主要能量来源转换"] E["产生蛋白质节约效应 (Protein Sparer)"] F["骨骼肌与瘦体重得到完整保留"] end A --> B B --> C C --> D D --> E E --> F ``` - **生长激素的合成代谢本质**：它不仅促进机体生长，更在热量归零时承担抗分解重任。 - **游离脂肪酸替代供能**：生长激素促使脂肪大量分解，替代葡萄糖成为身体细胞的主要动力。 - **84小时断食数据佐证**：受试者在跨入断食第48小时后，血液中的生长激素呈现飞跃式增长。 --- ### [10:55](https://www.youtube.com/watch?v=APZCfmgzoS0&t=655s) 生酮状态与运动：蒂姆·费里斯的断食实验教训断食者通常会在禁食开始后的前三天内逐步进入生酮状态（Ketosis）。具体进入的速度因人而异，主要取决于个人的日常活动量以及断食前的饮食结构。生酮状态是一个极佳的代谢风向标，标志着身体已经彻底打开了脂肪储备库，开始高效利用体内储存的体脂来维持生存。然而，如果在此期间完全剥夺运动，结果将截然相反。畅销书《巨人的工具》（Tools of Titans）作者蒂姆·费里斯（Tim Ferriss）便亲身经历过这种灾难性的反面教材。蒂姆在书中讲述了他第一次接受临床监护下的7天断食经历；当时出于医疗免责和责任风险的考虑，监管机构严禁他进行任何形式的运动，甚至不允许他离开监护中心的大楼。缺乏运动不仅无法加速耗尽体内的糖原储备，更直接扼杀了运动对生长激素的强效刺激机制，导致身体迟迟无法顺利进入生酮阶段。这种过度严苛且脱离代谢规律的静止断食，最终演变成一场肌肉浩劫——蒂姆在那次7天断食中足足流失了12磅肌肉。吸取惨痛教训后，蒂姆制定了一套旨在以最快速度诱导生酮的科学方案（包括在初期进行长达4小时的快走），随后他在一次长达10天的断食中，竟奇迹般地保持了肌肉零流失。 - **生酮时间窗口**：身体通常在断食的前72小时内完成糖脂代谢转换，运动量越大、前期碳水摄入越少，切换越迅速。 - **缺乏运动的双重打击**：静止不动既阻碍了肝糖原耗尽，又无法激发运动诱导的生长激素分泌，直接推迟生酮并诱发肌肉消耗。 - **蒂姆·费里斯的实证反差**：静卧监护7天惨失12磅肌肉，而配合4小时快走加速入酮的10天断食则完全没有损失瘦体重。 --- ### [11:56](https://www.youtube.com/watch?v=APZCfmgzoS0&t=716s) 亮氨酸的合成代谢作用与断食对比节食的最终总结生酮状态保全肌肉的另一大底层功臣是亮氨酸（Leucine）。当人体深处生酮状态时，空腹血液中的亮氨酸浓度会显著提升。作为支链氨基酸（BCAA）中最核心的成员，亮氨酸对人体具备极其强效的合成代谢诱导能力，能直接刺激蛋白质合成通路，从而牢牢守住人体的精瘦体重。许多健身增肌人群长期存在一种思维定势，认定断食或生酮饮食绝不适合力量训练者，因为传统理论认为肌肉合成离不开胰岛素的介导，因而必须依赖充足的碳水化合物；然而生理学事实证明，断食期间高浓度的亮氨酸完美填补了这一生态位，它自身就是一个强大的肌肉蛋白质合成触发器。全面审视断食与传统少吃节食的生理差异，二者的优劣一目了然。与那些让人疲倦不堪、代谢降低的传统低热量节食法相比，完全断食能让你以体脂的形式减掉更多体重，最大限度保留肌肉组织，赋予你更充沛的精力状态，而且完全不必忍受持续性的饥饿折磨。正如视频最后针对减重策略给出的精辟总结：“If proper weight loss is your goal, it might be better to eat nothing at all rather than eating a conventional low calorie diet.” - **亮氨酸的替代触发功能**：在缺乏高水平胰岛素和碳水化合物的情况下，升高的高浓度游离亮氨酸可独立触发蛋白质合成信号。 - **代谢产物全面逆袭**：断食绝非传统观念中“饥寒交迫”的消耗过程，而是通过生长激素、血酮与支链氨基酸协同构筑的自保代谢机制。 - **断食与传统节食的四大核心反差**： - **减脂效率**：断食减掉的体重绝大部分为纯脂肪，节食则往往夹杂大量水分与肌肉。 - **肌肉存留**：断食受生长激素和亮氨酸护航得以维系肌群，低热量节食则伴随基础代谢崩溃和肌肉分解。 - **机体活力**：断食激活交感神经与脂肪供能，精力充沛；节食则导致能量分配缩减，产生虚弱疲惫感。 - **饥饿体验**：断食期间随着酮体生成饥饿感逐渐钝化消退，少吃多餐则会让胰岛素波动持续诱发强烈的进食欲望。 ## Notable quotes > [11:56](https://www.youtube.com/watch?v=APZCfmgzoS0&t=716s) If proper weight loss is your goal, it might be better to eat nothing at all rather than eating a conventional low calorie diet. — Joseph Everett > [10:08](https://www.youtube.com/watch?v=APZCfmgzoS0&t=608s) growth hormone also mobilizes large quantities of free fatty acids from the adipose tissue, and these in turn are used to supply most of the energy for the body cells, thus acting as a potent "protein sparer. — Guyton and Hall Textbook of Medical Physiology > [03:00](https://www.youtube.com/watch?v=APZCfmgzoS0&t=180s) Again and again I have tried, but always with the same result: the light meals are just enough to keep me ravenously hungry... — Upton Sinclair ## Mentioned Joseph Everett, Angus Barbieri, Dr. Jason Fung, Upton Sinclair, Tim Ferriss, The Obesity Code, The Fasting Cure, Tools of Titans, Lehninger Principles of Biochemistry, Guyton and Hall Textbook of Medical Physiology, University of Dundee, Medical University of Vienna, Aarhus University Hospital, Minnesota Starvation Experiment ## Video description This is about the drastic physiological differences between fasting and eating less ▲Patreon: https://www.patreon.com/WILearned ▲Twitter: https://twitter.com/jeverettlearned ▲IG: https://www.instagram.com/jeverett.whativelearned/ *NOTE* One of the key things in being able to fast in a healthy matter is entering the state of ketosis - that is, switching your metabolism from burning carbohydrate to burning fat. *Considering most people have been burning carbohydrate their whole lives* this can make fasting a challenge. Upton Sinclair recommends doing quite long fasts - 12 days, but you may want to work your way up to longer fasts. Unless you are relatively keto adapted (or have experience with fasting of course), it's important that you take precautions while doing a fast. Fasting isn't inherently dangerous, *but diving into fasting when your body is in no way geared for it can be.* I recommend doing more research before doing longer fasts. "The Complete Guide to Fasting" (http://amzn.to/2tQjxXa) is a good book to start with. As Tim Ferriss puts it: Please don't do anything stupid and kill yourself. It would make us both quite unhappy. Just in case I should also say that of course you need to balance fasting with eating - You need to survive off of something. I have been doing intermittent fasting the past year (22 hours fasted, 2 hours eating - you can widen it to 16/8, which still provides great benefits) and will fast for a couple days every other month or so. Several other people have recommend a routine like this - Tim Ferriss recommends doing a 3 day fast once per month and a 7 day fast once per year. Also make sure you're getting enough fat, protein, micronutrients and fiber to maintain a healthy weight and healthy body - *excessive* fasting can be very dangerous. Books Mentioned: "The Obesity Code" by Dr. Jason Fung - http://amzn.to/2rXtalh "The Fasting Cure" by Upton Sinclair - (If you google the title you can find the full book online) "Tools of Titans" by Tim Ferriss - http://amzn.to/2rX6P7E [BLINKIST] Blinkist is an app I've been using lately to discover new books and review the ones I've already read. It gives you the key points in text or audio form from tons of different non-fiction books. Since I'm always going through so many books to get these done, it's very useful to get me exposed to more concepts beforehand to know if it's worth my time to buy and read through that particular book. Check it out here: http://bit.ly/2sbegMN For business inquiries: joseph.everett.wil@gmail.com [Source](https://www.youtube.com/watch?v=APZCfmgzoS0)

Source quotes

[11:56] Joseph Everett: If proper weight loss is your goal, it might be better to eat nothing at all rather than eating a conventional low calorie diet. [10:08] Guyton and Hall Textbook of Medical Physiology: growth hormone also mobilizes large quantities of free fatty acids from the adipose tissue, and these in turn are used to supply most of the energy for the body cells, thus acting as a potent "protein sparer. [3:00] Upton Sinclair: Again and again I have tried, but always with the same result: the light meals are just enough to keep me ravenously hungry...

Source quotes

[10:55] Joseph Everett: If proper weight loss is your goal, it might be better to eat nothing at all rather than eating a conventional low calorie diet.

Original transcript

[0:01] "Breakfast of champions." [0:03] What’s the difference between eating less food and eating no food? [0:06] Well, Let’s look at two different situations. [0:08] …In 1944, a study called the Minnesota Starvation Experiment was conducted and was designed [0:13] to understand the effects of caloric restriction on the body in order to gain some knowledge [0:18] that would help people starving in the aftermath of World War 2. [0:22] Thirty-six healthy men with an average height of 178cm (about five foot ten) and average [0:27] weight of 69.3 kilograms (or 153 pounds) were selected. [0:32] For three months, they ate a diet of 3200 calories per day. [0:35] Then, for six months they ate only 1570 calories. [0:39] However, caloric intake was adjusted to attempt to have the men lose 1.1 kilograms per week, [0:45] meaning some men got less than 1000 calories per day. [0:48] The foods given were high in carbohydrates- things like potatoes, turnips, bread and macaroni. [0:53] Meat and dairy products were rarely given. [0:56] During the six months, the men experienced profound physical and psychological changes. [1:00] Everyone complained that they were too cold. [1:02] One subject talked about having to wear a sweater in July on a sunny day. [1:07] The subjects’ body temperature dropped to an average of 95.8 degrees Fahrenheit (35.4 [1:10] degrees celsius). [1:12] Physical endurance dropped by half, and strength showed a 21 percent decrease. [1:16] The men experienced a complete lack of interest in everything except for food, which they [1:21] were obsessed with. [1:22] They were plagued with constant and intense hunger. [1:25] There were several cases of neurotic behavior like hoarding cookbooks and utensils. [1:29] Two participants had to be cut from the experiment because they admitted to stealing and eating [1:34] several raw turnips and taking scraps of food from garbage cans. [1:39] At first, the participants were allowed to chew gum, until some of the men began chewing [1:43] up to 40 packages a day. [1:46] Now compare all this to the case of Angus Barbieri, a Scottish man who in 1965 fasted [1:51] for over 380 days straight. [1:54] That is he took in no food whatsoever -nothing but water, black coffee and straight tea for [1:58] just over a year. [2:00] He lost 276 pounds, going from from 456 pounds to 180. [2:04] A case report published by the Dundee University Department of Medicine in 1973 said “...the [2:10] patient remained symptom-free, felt well and walked about normally,” and “Prolonged [2:15] fasting in this patient had no ill-effects.” [2:17] There were no complaints of mind numbing hunger and he kept the weight off- for several years [2:22] his weight stayed around 196 pounds. [2:25] This of course is not a perfect comparison, with the case of Angus, there’s only one [2:28] subject and his starting weight was drastically higher compared to those in the Minnesota [2:33] Experiment. [2:34] However, it does illustrate some very interesting points about just how different of a physiological [2:39] response you get from fasting (that is, eating nothing) compared to eating less, or caloric [2:44] restriction. [2:45] Dr. Jason Fung, a Toronto physician specializing in kidney disease, and author of the Obesity [2:51] Code, says that compared to fasting, Caloric Reduction will result in: less weight loss, [2:56] more lean mass loss (i.e. more muscle loss), and more hunger. [3:00] Let’s start by talking about hunger. [3:03] In Upton Sinclair’s 1911 book “The Fasting Cure,” he writes about fasting as a means [3:07] to improve health. [3:09] In describing his first couple attempts at fasting he writes “I was very hungry for [3:12] the first day-the unwholesome, ravening sort of hunger that all dyspeptics know. [3:17] I had a little hunger the second morning, and thereafter, to my great astonishment, [3:21] no hunger whatever-no more interest in food than if I had ever known the taste of it.” [3:27] Sinclair recommends to do quite long fasts - around 12 days or so. [3:31] In a section addressing concerns about fasting he writes “Several people have asked me [3:35] if it would not be better for them to eat very lightly instead of fasting, or to content [3:39] themselves with fasts of two or three days at frequent intervals. [3:43] My reply to that is that I find it very much harder to do that, because all the trouble [3:47] in the fast occurs during the first two or three days. [3:50] It is during those days that you are hungry.” [3:53] Then he says: “...perhaps, it might be a good thing to eat very lightly of fruit, instead [3:57] of taking an absolute fast-the only trouble is that I cannot do it. [4:01] Again and again I have tried, but always with the same result: the light meals are just [4:05] enough to keep me ravenously hungry...” [4:07] In the book he says you will know when you should finish fasting, because your hunger [4:11] will “return.” [4:12] He quotes a letter he received from a 72 year old man saying “After fasting twenty-eight [4:17] days I began to be hungry, and broke my fast with a little grape juice, followed the next [4:22] day with tomatoes, and later with vegetable soup. [4:25] ” [4:26] He quotes several other letters he received from readers and this disappearance and reappearance [4:29] of hunger is a common theme. [4:31] Everyone who wrote to him fasted for at least 10 days, saying they only broke their fast [4:36] when hunger “returned.” [4:38] This phenomenon runs contrary to the idea one would get hungrier and hungrier as long [4:43] as they don’t eat. [4:44] However, most people have experienced for themselves that this is not the case. [4:48] Some will find that they are not hungry at all in the morning or at least they are not [4:52] as hungry as they are for lunch or dinner. [4:54] But unless you are eating in your sleep, the morning is when you have gone the longest [4:58] without food. [5:00] Some of this can be explained by the hormone Ghrelin. [5:03] Ghrelin, known as the “hunger hormone” has been found to increase appetite and weight [5:07] gain. [5:08] A study at the Medical University of Vienna looked at patients participating in a 33 hour [5:13] fast. [5:14] Their ghrelin levels were checked every 20 minutes. [5:16] Here’s how the levels changed over time. [5:20] What’s interesting is ghrelin is lowest at 9:00AM, which is when they have gone the [5:24] longest without eating. [5:26] And, Ghrelin comes in waves and overall doesn’t rise during the period the subjects were fasting. [5:32] Then, As you can see, ghrelin rises in sync with normal lunch and dinner times, as if [5:36] the body had learned to expect food at that time. [5:39] However, that ghrelin rise spontaneously decreases after 2 hours without food. [5:45] I’ve experienced this kind of spontaneous decrease in hunger myself many times when [5:49] I was working as a consultant. [5:51] Lunch time would come and I would be hungry, but I was too busy to eat so I just kept working. [5:56] Pretty quickly I forgot about eating and wasn’t particularly hungry until dinner time. [6:01] This is very helpful to keep in mind if you’re doing a long fast or even if you’re starting [6:04] intermittent fasting - you’re going to get annoying waves of hunger, especially around [6:09] the times that you usually eat. [6:10] But, it won’t get worse, the hunger will simply go away if you are patient. [6:16] Another study concerning ghrelin was done at Aarhus University Hospital in Denmark and [6:20] it shows what happens if you do a longer fast. [6:23] They looked at the ghrelin levels of 33 subjects who fasted for 84 hours. [6:27] So, did they get increasingly hungrier throughout the fasting period? [6:31] Well, No. [6:32] Their ghrelin followed similar rhythms each day but actually decreased the longer they [6:37] fasted. [6:38] Going longer without food actually made them less hungry. [6:42] This gives credence to what Upton Sinclair and his readers said about hunger disappearing [6:46] after the first 3 days of fasting. [6:47] I’ve done a couple 5 and 6 day fasts in the past myself and this was indeed the case. [6:52] Actually, I did a 4 day fast last week and again the 4th day was when I had the least [6:58] hunger. [6:59] Another thing that may be contributing to this phenomenon is that you are entering ketosis. [7:04] Ketosis is a physiological state where your metabolism switches to using primarily fat [7:09] for energy. [7:10] For this reason ketosis is popular as a weight loss method, but it has many other benefits [7:15] including better physical and mental efficiency. [7:18] Ketosis occurs when you restrict carbohydrates down to 50 grams or less and you don’t eat [7:22] too much protein. [7:23] Everyone’s body is a bit different so you might have to eat even less carbohydrate or [7:28] may have room for more, but the recommended ratio of a ketogenic diet is to get 5% of [7:32] your calories from carbs, 25% from protein and 75% from good fat. [7:37] A simpler way to enter ketosis is just don’t eat anything for a long enough time. [7:43] This is one of the major points in the difference between fasting and caloric restriction. [7:47] The problem with the subjects in the Minnesota Starvation experiment was that they were eating [7:51] just enough to keep them out ketosis and keep their metabolism primed for burning carbohydrate [7:56] (glucose), so they couldn’t use their body fat for energy. [8:00] This explains a lot of things like why they were losing their strength and were very sluggish [8:04] and cold. [8:05] It also clears up why Upton Sinclair said fruit or light meals were just enough to keep [8:09] him ravenously hungry and far weaker than if he had just eaten nothing. [8:15] As I explained in my last video, insulin is necessary for glucose to get into the cell [8:19] to be used for energy. [8:21] When you eat carbohydrates, the pancreas secretes insulin to deal with it and too much insulin [8:26] hampers the action of something called hormone sensitive lipase which is necessary to mobilize [8:31] fat and use it for fuel. [8:33] Though, keep in mind that grains or refined carbohydrates will provoke a much higher insulin [8:39] response than say green vegetables. [8:42] Now because the body is having a hard time using its fat for fuel, it will do a couple [8:47] things: One, it will simply slow down metabolism to preserve energy. [8:52] In the Minnesota Starvation experiment, the subjects metabolism dropped by 40 percent. [8:57] Their bodies didn’t have access to its stored energy, and their restricted calorie diets [9:01] don’t provide much fuel so there’s no choice but to slow down the metabolism. [9:06] Ironically, in the case of fasting, as Jason Fung points out - metabolism actually goes [9:11] up. [9:12] "If you don't do anything about your insulin and just reduce your calories, your metabolism [9:17] goes down. [9:18] But what happens during fasting? [9:19] Well, here's a study of 4 consecutive days of fasting. [9:24] What happens to your REE - this is this middle line here, that's the resting energy expenditure. [9:30] It doesn't go down, it goes up. [9:34] You're burning more energy than you did." [9:38] The other thing the body will do when it can’t use fat for fuel is break down muscle into [9:43] glucose through a process called gluconeogenesis. [9:47] The body doesn’t want do this too much because it’s not very smart to completely eat through [9:50] something as important as muscle, but when it can’t access its own stored energy it’s [9:56] more likely to resort to this. [9:58] This is why you’ll experience more muscle loss on caloric restriction than if you ate [10:02] nothing. [10:04] When you are fasting, Human Growth Hormone is released. [10:08] As the name implies, Human Growth Hormone is an anabolic hormone - a hormone conducive [10:12] to growth. [10:14] In Leningher’s Principles of Biochemistry textbook they give the example of how injecting [10:18] the human growth hormone gene into a mouse makes it unusually large. [10:24] As explained in Guyton’s Textbook of Medical Physiology: "...growth hormone also mobilizes [10:28] large quantities of free fatty acids from the adipose tissue, and these in turn are [10:33] used to supply most of the energy for the body cells, thus acting as a potent "protein [10:38] sparer." [10:39] "That is human growth hormone is protecting your muscles from breaking down. [10:44] The study I referred to earlier about subjects undergoing an 84 hour fast shows that growth [10:49] hormone rises significantly after the second day of fasting. [10:55] As mentioned earlier, you should enter ketosis sometime within the first 3 days or so of [10:59] fasting, and it depends on how much you are moving around and what your diet was like [11:04] before starting the fast. [11:05] The state of ketosis is a great indicator that your body is making good use of its stored [11:10] body fat for energy. [11:13] In Tim Ferriss’ book “Tools of Titans,” Tim talks about his first clinically supervised [11:18] 7 day fast. [11:19] For some sort of liability reasons, he wasn’t allowed to exercise or leave the facility. [11:24] Considering exercise is a potent stimulator of human growth hormone and will help deplete [11:29] glucose stores, not getting any exercise is a great way to prevent yourself from getting [11:33] into ketosis during a fast. [11:35] It’s also a great way to lose muscle. [11:38] Tim says he lost 12 pounds of muscle during the overly restrictive clinically supervised [11:43] 7 day fast. [11:44] But, when following a protocol designed to get him into ketosis as soon as possible - involving [11:49] things like 4 hours of brisk walking, he did a ten day fast and apparently lost zero muscle [11:55] mass. [11:56] One last factor in Ketosis preserving muscle is leucine. [12:00] When you're in ketosis, you have a higher fasting blood leucine level. [12:03] And leucine is a key branch chain amino acid that has an anabolic effect on the body so [12:08] it preserves lean body mass. [12:10] A lot of people interested in building muscle may be worried that fasting or a ketogenic [12:15] diet wouldn’t work for them because insulin and therefore carbohydrates are necessary [12:19] for protein synthesis (i.e. muscle growth), but actually this leucine fills that role [12:25] and is a good trigger for protein synthesis. [12:28] So, just to sum all this up: compared to a conventional calorie restricted diet, fasting [12:34] means you lose more weight in the form of fat, you keep more muscle, you have more energy, [12:39] and you are less hungry . If proper weight loss is your goal, it might be better to eat [12:44] nothing at all rather than eating a conventional low calorie diet.