the dangers of fasting and starvation

Fasting has been done for hundreds if not thousands of years by people for religious reasons and has recently become a popular activity among people wanting to improve their physical health. Does fasting benefit the body or is it perpetuating stress and making their health worse?

To fast is to go without food, to go hungry, or to starve oneself.  We’ve all seen pictures of starving children who are nothing but skin and bones. If starving oneself is healthy, then those children must be the epitome of health, right?

According to Wikipedia, starvation “is the most extreme form of malnutrition. In humans, prolonged starvation can cause permanent organ damage and eventually, death.”

In this presentation you’re about to learn the detrimental physiological effects of fasting on human health.  The goal is to give you biological evidence-based perspective on how the body works and what happens when it is deprived of food.  I hope you learn something valuable and it enables you to improve your health.

(Click here to watch on YouTube)

The Physiology of Fasting & Starvation

At any given time your blood contains a certain amount of glucose and a certain amount of glucose is stored in your muscles and liver in a form called glycogen. During a fast, your body will first use the glucose available in the bloodstream – and once that has been exhausted, it will use your glycogen stores until they too are exhausted.

This complete absence of sugar is called hypoglycemia.  Hypoglycemia is an absolute emergency; if sugar is not obtained quickly, you will die. Eating a piece of fruit will help provide essential sugars, but during a fast the body has to get its energy elsewhere… 

Where does the energy come from during a fast?

Instead of using energy obtained from food, during a fast the body has no choice but to begin eating itself for energy.  The body will begin breaking down your muscles, brain, organs and other soft tissues into amino acids, which will be used to manufacture sugar.  Fat stores will also be broken down into free fatty acids and released into the blood stream for energy use.

The primary hormones responsible for the breakdown of soft tissues into amino acids and of fat stores into free fatty acids are the stress hormones cortisol and adrenaline, respectively.

“Since your body would eat itself to death in a couple weeks, the body slows down its metabolic rate so we can get by on less calories.  Brain function, reproductive function, digestive function and the function of everything is slowed to prevent death.”[1]
– Dr. Raymond Peat

The stress cascade during fasting and starvation

Mainstream Perspective on Fasting

According to the National Institute on Aging, “Some study results suggest that calorie restriction may have health benefits for humans, but more research is needed before we understand its long-term effects.”

“[Human] studies,” they continue “have also found many other physiologic effects whose long-term benefits and risks are uncertain, as well as reductions in sexual interest and the ability to maintain body temperature in cold environments.”[2]

national institute on aging perspective on fasting and caloric restriction

Does a reduction in sexual interest sound healthy to you?  The classic example of stress is when a person is running away from a hungry tiger.  In this ‘fight or flight’ situation, survival is all that matters; reproduction is one of the least important things.  This explains why people fasting lose sexual interest: During a fast/starvation/stress, reproductive function is sacrificed to improve immediate chances of survival.

How about the ability to maintain body temperature?  Does that sound healthy?  In the human body, thyroid hormone is responsible for heat production.  The evidence showing lack of ability to maintain body temperature in people fasting or who have fasted long term suggests thyroid function has been suppressed – a subject we will get into next.

Fasting Inhibits Thyroid Hormone

The active thyroid hormone T3 is essential for health.  It is responsible for heat production and determines your metabolic rate.  The thyroid gland itself produces a small amount of T3, but mostly T4, which is then converted into T3 by the liver.

The enzyme within liver cells responsible for converting T4 to T3 is regulated by the amount of glucose in those liver cells.  During fasting, at first the glycogen stores within the liver cells will allow for T3 production, but once that glycogen is depleted T3 production will cease.

During stress, the free fatty acids released into the bloodstream inhibit the use of glucose (the randall cycle) so T4 will not be converted into T3.[3]

Fasting Increases Toxins in the Body

omega-6 droplet released as free fatty acids into the blood during stress and fasting
The omega-6 relesed from tissues during stress will be broken down into toxic fragments like prostaglandins, which reinforce stress.

The fats released during fasting will be mostly all polyunsaturated fatty acids (PUFA), which break down into toxic metabolites, one of which is called prostaglandins, and is critical for the formation of cancer.[4] 

The older you are, the more PUFA will be in your tissues and the more dangerous fasting becomes.

Fasting Inhibits Detoxification

Not only does fasting increase toxins in the body, but it reduces the liver’s ability to detoxify those chemicals after they are produced. The fats released during fasting will be mostly all polyunsaturated fatty acids, which break down into toxic metabolites and cause damage to cytochrome P450 enzymes.

“The results demonstrate that most of the unsaturated fatty acids showed marked inhibition” of detoxification enzymatic activities.[5]  Fasting reduces the liver’s ability to detoxify chemicals from the body.

Fasting Inhibits the Immune System

During a fast, the immune system is inhibited in a number of ways.

The immune system is inhibited during a fast
The immune system is inhibited during a fast in a number of ways.

The first tissue to be consumed during stress is the thymus gland, which is essential for immune system function.  This is based on autopsy studies of elderly people which found their thymus glands were completely gone.[6]

The polyunsaturated fatty acids (PUFA) released during stress are so potently immunosuppressive that they’ve been administered as drugs to kidney transplant patients for decades to disable their immune systems and prevent their bodies from rejecting the foreign tissue.[7]

One way they do this is by directly killing white blood cells, which are the most important part of the immune system.[8]

Fasting Increases Risk of Cancer

Fasting increases the risk of developing cancer in a number of ways.  Here are 3 of those ways:

  1. During stress, lactic acid production is increased, which directly promotes cancer growth and metastasis.[9]
  2. Muscle tissue, which is broken down during stress, contains a high concentration of the amino acid tryptophan, which is a precursor to serotonin.  Serotonin is increased during stress and has been shown in numerous studies to directly promote tumor growth.[10]
  3. Dr. Otto Warburg found in the 1930’s that cancer was a disease of impaired oxygen use by cells – and thyroid hormone is essential for cellular oxygen use.  The polyunsaturated fatty acids released during stress/fasting/starvation inhibit thyroid function in at least 6 ways.

Does Fasting Increase Lifespan?

Beginning in 1935[11], studies have reported that caloric restriction can extend lifespan in various animals.  Looking closer, scientists have found reduced production of reactive oxygen species (ROS) and oxidative stress to be the mechanisms.

However, in 1993 it was discovered that by subjecting rats to a diet restricting the amino acid methionine, lifespans were extended similarly to ones subjected to caloric restriction.[12

In other words, it’s not the absence of food that causes increased longevity but the absence of methionine.  The reduction in methionine consumption is responsible for the reduction in oxidative stress and life extension seen in fasting.[13][14]

Health Benefits of Fasting?

By not eating during a fast, your intestines are given a break from dealing with toxins and undigestable materials in food. Endotoxin is a byproduct of the bacterial fermentation of undigestable foods within the gastrointestinal tract. The lack of food consumed during a fast means gut bacteria are deprived of food and the gut is sterilized.

Fasting prevents endotoxin production within the gut
Fasting is beneficial in that it reduces the amount of endotoxin produced by gut bacteria.

This means that fibrous food materials won’t be metabolized by bacteria into the chemical endotoxin (lipopolysaccharide).  Thus the body is relieved of having to deal with this constant toxic burden. Of course, this same benefit can be had without fasting simply by not eating undigestable foods like beans, grains, nuts, and raw vegetables.

How to Minimize the Damage of Fasting

fruit and vegetable juice fast
Fruit and fruit juice is a good way to prevent stress from breaking down muscle tissue.

For those who realize that fasting is damaging to the body but still wish to do it for whatever reason, it’s important to note the ways in which the damage can be minimized.

According to Peat, “During stress or fasting, the loss of tissue protein can be minimized by supplementing the minerals, potassium, sodium, magnesium, and calcium.

A good way to get these minerals is to do a juice fast including fruit and vegetable juices.

Furthermore, “Eating carbohydrates (especially fruits) can allow the liver to resume its production of T3,” according to Dr. Raymond Peat.[3]


Depriving the human body of food activates stress in the body, which results in a cascade of detrimental physiological effects that lead directly to disease and degeneration.  Some of the detrimental effects of fasting include:

  1. Fasting inhibits thyroid hormone
  2. Fasting increases toxins
  3. Fasting inhibits detoxification
  4. Fasting inhibits the immune system
  5. Fasting increases risk of cancer

The moral of the story?  Don’t starve yourself!  Nourish your body with foods that promote health like well-cooked vegetables, fresh fruit, dairy, seafood, animal liver and gelatinous soups and stews.

Thanks for reading!  Don’t forget to write a comment below to let us know one thing you learned from this presentation.


  1. Ray Peat on Fasting [Video]
  2. Calorie Restriction and Fasting Diets_ What Do We Know [Article]
  3. An Interview With Dr. Raymond Peat_ A Renowned Nutritional Counselor Offers His Thoughts About Thyroid Disease _ Thyroid Disease Information Source – Articles_FAQs [Article]
  4. Ray Peat on fasting and weight loss, cortisol’s effect on muscles and organs [Video]
  5. Inhibition of cytochrome P450 enzymes by saturated and unsaturated fatty acids in human liver microsomes, characterization of enzyme kinetics. [Study]
  6. Cepeda S, Griffith AV. Thymic stromal cells: Roles in atrophy and age-associated dysfunction of the thymus. Exp Gerontol. 2018;105:113-117. [Study]
  7. Mertin J. Letter: Unsaturated fatty acids and renal transplantation. Lancet. 1974;2(7882):717. [Study]
  8. C.J. Meade and J. Martin, Adv. Lipid Res., 127, 1978. [Cited in Article]
  9. Dhup S, Dadhich RK, Porporato PE, Sonveaux P. Multiple biological activities of lactic acid in cancer: influences on tumor growth, angiogenesis and metastasis. Curr Pharm Des. 2012;18(10):1319-30. [Study]
  10. Soll C, Jang JH, Riener MO, et al. Serotonin promotes tumor growth in human hepatocellular cancer.  Hepatology. 2010;51(4):1244-54. [Study]
  11. Mccay CM, Crowell MF, Maynard LA. The effect of retarded growth upon the length of life span and upon the ultimate body size. 1935. Nutrition. 1989;5(3):155-71. [Study]
  12. Orentreich N, Matias JR, Defelice A, Zimmerman JA. Low methionine ingestion by rats extends life span. J Nutr. 1993;123(2):269-74. [Study]
  13. Gallinetti J, Harputlugil E, Mitchell JR. Amino acid sensing in dietary-restriction-mediated longevity: roles of signal-transducing kinases GCN2 and TOR. Biochem J. 2013;449(1):1-10. [Study]
  14. Caro P, Gomez J, Sanchez I, et al. Forty percent methionine restriction decreases mitochondrial oxygen radical production and leak at complex I during forward electron flow and lowers oxidative damage to proteins and mitochondrial DNA in rat kidney and brain mitochondria. Rejuvenation Res. 2009;12(6):421-34. [Study]