Ray Peat on Adaptation

September 26, 2025

The Costly Adaptations of Serotonin Production

"Stress of various kinds increases the production of serotonin and various pituitary hormones, leading to adaptations of the organism but at the cost of inflammation and degeneration. Studies on several pituitary hormones have shown that they have aging-accelerating effects, leading to edema, inflammation, fibrosis, and reduced lifespan. W.D. Denckla's experiments, which demonstrated the enormous life-extending effect of removing the pituitary gland while simultaneously supplementing thyroid and glucocorticoid hormones, suggest possibilities for finding ways to prevent the overproduction of serotonin and its associated hormones and cytokines."

– September 2019 – Ray Peats Newsletter

Criticism of the Scientific Approach to Organismic Adaptation

"Official science, by defining the organism and environment according to its ideology of mechanistic reductionism, has radically misrepresented the nature of organismic adaptation."

– September 2017 – Ray Peats Newsletter

Environmental Influence on Physical Development

"When our environment shrinks, when there is not enough food, we can adapt, for example by replacing muscle with fat and by having babies with small brains (the brain is an energetically expensive organ, even though its efficiency increases with its cost). When our environment meets our needs, our brain and muscles grow. The lower leg (like the brain) is a good indicator of environmental support: parents who grew up in a population with atrophied-looking lower legs can have children with well-developed legs if milk becomes abundantly available."

– Nutrition For Women

Estrogen Increase Due to Stress and Its Effects on Male Behavior

"Stress leads to an increase in estrogen and a loss of anti-estrogens such as thyroid, progesterone, and (in men) testosterone. Male monkeys that are bullied have lowered testosterone levels, and this effect persists long after their environment has improved. The stress of submission seems to lead to an adaptation in the form of passivity. Their passivity prevents further injury, but we do not know how stressful their continued submission is."

– Nutrition For Women

Selye's Discovery of the Phases of the Adaptive System and Stress Immunization

"Hans Selye found that the adrenals are a main component of our adaptive system. In the first stress phase, there is a shock reaction (with changes resembling those of estrogen dominance), with injuries to various tissues. In the second phase, the adrenals protect the animal, and this protection lasts until something is exhausted. By exposing rats to preliminary stress, Selye found that he could induce adaptation to other, later stressors – a kind of immunization against stress."

– Nutrition For Women

Adaptive hypothyroidism due to stress and intense exercise

"Cortisone also inhibits the thyroid. Any stress, including intense exercise, causes this protective slowing of metabolism. The slow heartbeat of runners is largely the result of this adaptive hypothyroidism."

– Nutrition For Women

Conversion of thyroid hormones during stress and aging

"When a baby is born or when a person experiences other stress, such as an infection, or when a person ages, the best-known thyroid hormone, thyroxine, is not converted into the more active form T3 (triiodothyronine) in the usual way. In these emergency situations, reduced oxygen consumption is a useful adaptation."

– Nutrition For Women

Selye's stress phases and their effects on tissues

"Selye divides stress into three phases: alarm, resistance (or adaptation), and exhaustion. Three tissues usually show effects first: thymolymphatic tissue shrinks, gastrointestinal tissue becomes inflamed and bleeds, and the adrenal cortex enlarges."

– Nutrition For Women

Maternal adaptation to fat and infant dependence on glucose

"During pregnancy, the mother's body adapts to increasingly live off fat, so that most of the available sugar can be used by the baby. The brain consumes most of the body's glucose, so mental fatigue can slightly affect blood sugar levels. The developing baby is extremely dependent on glucose as an energy source, and its brain can be damaged by sugar deprivation."

– Nutrition For Women

Pregnancy, similarities to diabetes, and blood sugar trends

"Pregnancy itself resembles diabetes, through the adaptation to fat oxidation instead of sugar, so a slight tendency to diabetes can be seen as support for the pregnancy. Older women are more likely to have some degree of diabetes or elevated blood sugar. With each pregnancy, there is a tendency for blood sugar to be higher and the baby to be larger and more premature."

– Nutrition For Women

Chronic diet adaptation and loss of protein tissue

"Chronic dieters can adapt to a low calorie intake (Lancet, April 5, 1975, Miller and Parsonage). This is likely partly due to a loss of active protein tissue. A comprehensive diet is necessary to replace such tissue."

– Nutrition For Women

Recommended slow diet transition for enzyme adaptation

"A switch to a new diet or ending a fast should be done gradually, allowing at least a few days for enzyme adaptation."

– Nutrition For Women

Exercise training, stress hormones, and thyroid function

"It is known that exercise training slows the pulse. Cortisone produced by stress inhibits the thyroid. (When the thyroid is low, less oxygen is needed, which is a useful adaptation to increase endurance.) These hormonal changes are now known to cause infertility in men and women."

– Nutrition For Women

Role of demand and reserve capacity in physiological adaptation

"The greater the demand, the smaller the reserve capacity for future adaptation will be. Therefore, part of our physiology is to adjust our environment to better meet our needs."

– Nutrition For Women

Metabolic energy as a constant adaptation process

"If the organism is seen as a constant adaptation process, rather than a machine that must make do with parts formed in early youth, metabolic energy is recognized as something constructive, and things that reduce our energy – such as a lowering of body temperature – are seen as threats to life and successful adaptation."

– November 2020 – Ray Peats Newsletter

The adaptive role of inflammation and its long-term consequences

"Inflammation is a type of adaptive response, but it leaves fibrotic changes and atrophy of functional cells as well as an increased tendency to revert to the inflammatory response."

– November 2020 – Ray Peats Newsletter

Environmental influences on longevity and inflammation

"If lifespan is shortened by the accumulation of changes resulting from inflammatory adaptations, then living in different environments that require various types of adaptations will cause significant changes in lifespan."

– November 2020 – Ray Peats Newsletter

Lifestyle choices to slow aging and promote longevity

"Altitude and a milk-based diet are obviously two important thermogenic factors that slow the accumulation of harmful adaptations, but there are many other controllable factors that could extend longevity even further. Reducing inflammatory factors is important, and personal choices can make a big difference, such as choosing easily digestible foods to reduce endotoxin, avoiding polyunsaturated fatty acids that disrupt cellular respiration and form inflammatory prostaglandins, avoiding antioxidant supplements that create a reductive excess, and choosing foods that contain anti-inflammatory thermogenic compounds, like citrus fruits with their high flavonoid content that support cellular respiration functions."

– November 2020 – Ray Peats Newsletter

Stress-Induced Serum Cholesterol as an Adaptive Response

"The rise in serum cholesterol during stress is an important protective adaptation."

– November 2018 – Ray Peats Newsletter

Urgency of Returning to Holism for Understanding Developmental Processes

"The holistic view of the organism and its adaptation potentials, advocated by Hippocrates and Aristotle, was rejected by the new science of recent centuries. Regaining and creatively using this perspective has become urgent if we want to understand the processes of development, including aging and degenerative diseases."

– November 2017 – Ray Peats Newsletter

Organismic Responses Depend on Historical, Conditional Factors

"In reality, every adaptive situation involving a response to a single substance or stimulus affects the whole organism, not just a single receptor substance. The reason why an organism's response to a particular stimulus increases or decreases depends on the organism's history and condition as well as the nature and intensity of the stimulus. Different aspects of the organism are influenced by different substances or forces as well as by varying amounts of these substances or forces."

– November 2017 – Ray Peats Newsletter

Prenatal Influences on Brain Development and Adaptability

"Experiments over the last 60 years have shown that more or less glucose, carbon dioxide, heat, and progesterone during embryonic and fetal development can influence brain growth and the way the brain controls future development and adaptability."

– November 2017 – Ray Peats Newsletter

Survival Mechanisms of the Brain in Stressful Environmental Interactions

"In mediating adaptation, the brain aligns the organism with aspects of the environment that are most likely to satisfy its needs, and this includes assessing possible future situations. In the absence of good prospects, the brain engages in defensive changes, increases stress hormones, the fight-or-flight mechanisms, and begins to convert some of its own tissues into energy and materials needed for the survival of its vital organs – brain, lungs, and heart."

– November 2017 – Ray Peats Newsletter

Inflammatory Conditions and Activation of the DNA Exosome System

"The conditions that trigger inflammation activate the adaptive exosome system, a retrotransposon system that encompasses a massive block of our DNA and overlaps with the virus production mechanism."

– May 2020 – Ray Peats Newsletter

Humans as epigenetic, adaptive beings

"We are not defined as somas produced once by our DNA, but as adaptive, epigenetic, continuously creative beings."

– May 2020 – Ray Peats Newsletter

Effects of respiratory adaptation at different altitudes

"The fundamental principles of respiration, the Bohr and Haldane effects, describe the physical equilibria of oxygen and CO2 in humans adapted to life at different altitudes. The Haldane effect describes the fact that increased oxygen pressure reduces the amount of carbon dioxide retained by hemoglobin, and decreased oxygen pressure increases the amount of retained CO2. A steady increase in retained CO2 with increasing altitude occurs in those who adapt. People who do not adapt experience a loss of CO2 with a rise in lactate."

– May 2020 – Ray Peats Newsletter

Retrovirus ancestry and protective functions of exosomes

"After the protective and adaptive functions of exosomes and retrotransposons have been clarified, the more obvious conclusion might be that we are the ancestors of retroviruses."

– May 2020 – Ray Peats Newsletter

When adaptive stress becomes maladaptive

"Stress is experienced when processes that are normally adaptive produce maladaptive effects. This happens when the organism's resources are insufficient to meet the demands of the situation."

– May 2019 – Ray Peats Newsletter

Embryo adaptation to intrauterine disturbances

"Experimental embryology has made it clear that development is an intentional process. An embryo can survive extreme disturbances by adjusting its structures and metabolism, but these adaptations to difficult intrauterine conditions can sometimes make adjustments during childhood problematic."

– May 2018 – Ray Peats Newsletter

Energy consumption of the brain during adaptation and simplification

"The brain has an extremely high metabolic rate and uses energy to adapt to the constant influx of sensory information from the body and its environment. When energy is lacking, it reduces and simplifies. With full energy, it builds an ongoing model of itself and the things it interacts with – each of which is a process. In a state of mental energy deficiency, things become categories instead of processes, and they do not take up space in an ongoing life story."

– May 2018 – Ray Peats Newsletter

Cancer as a development-related adaptive process

“If cancer is seen as an event in the body's developmental and adaptive processes, the important question is to understand the process so that the response can be changed – reducing harmful factors and supporting adaptive and corrective factors.”

– May 2016 – Ray Peats Newsletter

Personalized therapy through understanding adaptation history

“To address the specific problem of a particular person, we need the best knowledge about how the history and current situation of an organism affect its ability to adapt to new situations, as well as knowledge about the therapeutic resources available.”

– May 2016 – Ray Peats Newsletter

McClintock's discovery of gene movement in plants' stress response

“In the 1940s, Barbara McClintock discovered that plants under stress can move their genes to improve adaptation by generating more variation in offspring. Instead of admitting that McClintock had discovered an aspect of life's creativity, they found the adaptive flexibility she discovered unbearably alien to their mechanistic understanding of life.”

– March 2021 – Ray Peats Newsletter

McClintock's research on viral evolution and epigenetics

“A simple shift in perspective can solve some old puzzles, such as how millions of virus species originated, since viruses cannot reproduce themselves without the organisms they infect, and why our cells would retain such an immense amount of useless or harmful DNA if our DNA had evolved by eliminating parts that did not contribute to fitness. McClintock's work has led to an answer to these questions as well as a foundation for understanding the intelligence of epigenetics and the inheritance of adaptations. The ‘dark DNA’ functions during embryonic development by mediating the effects of the intrauterine environment.”

– March 2021 – Ray Peats Newsletter

Bacterial adaptation and similar human genetic mechanisms

“James Shapiro's work with bacteria shows that they – supposedly one of the simplest life forms – have a ‘read-write’ genome and, by understanding their situation, can change their genes to adapt to problem situations. It is becoming increasingly clear that we have similar abilities to bacteria, with dark DNA being part of this adaptive system.”

– March 2021 – Ray Peats Newsletter

Adjustment problems of premature infants in new environments

“The premature infant, suddenly leaving its low-oxygen, CO₂-rich, sugar-rich environment and exposed to the extremely new environment of a hospital incubator, is an extreme example of how our normal adaptive responses can become destructive when misdirected by an unfavorable environment.”

– March 2021 – Ray Peats Newsletter

Tissue Changes Over a Lifetime Due to Environmental Factors

“The normal person living for many years in an environment with limited amounts of the most supportive factors and varying amounts of many harmful factors experiences a gradual accumulation of tissue changes caused by misguided adaptive factors.”

– March 2021 – Ray Peats Newsletter

Oxidative Metabolism Maintains Protective Factors After Pregnancy

“In childhood and maturity, a strong oxidative metabolism can maintain some of the essential protective factors of pregnancy, including adequate amounts of glucose and carbon dioxide, good temperature regulation, and avoidance of overproduction of superoxide and lactate. Under these conditions, cytokines can contribute to adaptation and ongoing development.”

– March 2021 – Ray Peats Newsletter

Life, Adaptation, and Epigenetic Legacy

“Life is adaptation, every adaptation involves epigenetic modifications of the differentiation state, and every epigenetic change has transgenerational effects.”

– March 2019 – Ray Peats Newsletter

Pro-inflammatory Environments and Epigenetic Limitations

“Our organisms undergo continuous processes of adaptive changes in response to our pro-inflammatory environments, which include epigenetic changes that limit our potentials and risk cumulative effects in subsequent generations.”

– March 2019 – Ray Peats Newsletter

Prenatal Influences and Development of Autistic Traits

“Today’s knowledge about prenatal influence on the development of autistic traits, in humans and lab animals, aligns with Pavlov’s observation that some animals were overwhelmed by stimulation that others could easily adapt to.”

– March 2018 – Ray Peats Newsletter

Metabolism: Adaptive Interactions in Organisms

“The idea of metabolism – substance change, adaptive interaction – implicitly includes the interactions of cells with the organism in its environment.”

– March 2017 – Ray Peats Newsletter

Overlooked Stress Effects on the Gut

“While the effects of stress on the gut have been known since Hans Selye described the general adaptation syndrome (with gut bleeding as an early sign of stress), they were not considered in any of the major studies on brain trauma or stroke.”

– March 2016 – Ray Peats Newsletter

Serotonin: More Than Just a Neurotransmitter

"Serotonin is often called a neurotransmitter and considered a substance that acts on receptors to transmit information, possibly processed like computers process digital information. I think it is more useful to view it in terms of fields and formative processes that determine how the organism uses energy to adapt to stress and opportunities. It is involved in the energetic and structural changes that occur during stress and adaptation."

– July 2019 – Ray Peats Newsletter

Exploring Futures Through Adaptive Physiology

"Adaptive physiology (rejecting the doctrine of timeless properties) deals with where we are going, what we become, and what possibilities we have. The subject it studies requires attention to context and temporal processes."

– July 2017 – Ray Peats Newsletter

The Symphony of Life: Embracing Its Complexity

"The organism's metabolism is a single, integrated process in which every part must adapt to the conditions of the other parts. Our nerves contain chemical receptors that detect changes in metabolic chemicals in the blood, allowing the organism to make adaptive changes."

– July 2017 – Ray Peats Newsletter

Drastic Demand Reduction in Unfavorable Environmental Conditions

"When environmental conditions are too poor for active adaptation, many organisms can drastically reduce their needs."

– January 2021 – Ray Peats Newsletter

Harsh Environments: Early Reproduction and Energy Adaptation

"The stresses of a harsh environment, which make early reproduction advantageous or require accelerated tissue renewal, also favor epigenetic adaptations that reduce energy demand."

– January 2016 – Ray Peats Newsletter

Adaptive Role of Estrogen in Hibernation

"The increase of nitric oxide and/or hydrogen sulfide by estrogens is adaptive for a hibernating animal, as it reduces its body temperature and metabolic rate."

– January 2016 – Ray Peats Newsletter

Epigenetic Changes Through Stress Adaptation

"In all these conditions of stress adaptation, epigenetic modifications of DNA are involved, with nitric oxide together with estrogen and other hormones participating in DNA methylation and histone modification as well as a variety of other biochemical, longer-lasting modifications."

– January 2016 – Ray Peats Newsletter

The Double-Edged Role of Nitric Oxide

"Although a primitive adaptive system like nitric oxide can be useful for a species, it can be harmful to individuals."

– January 2016 – Ray Peats Newsletter

Harmful Effects of Prolonged Cortisone During Stress

"Meerson's work has shown in detail how the normally beneficial adaptation hormone, cortisone, can cause so many other harmful effects when its action lasts too long or is too intense."

– Generative Energy – Restoring The Wholeness Of Life

Limitations of Cortisone Without Treating the Causes

"Although cortisone supplementation can help with a variety of stress-related diseases, no cure will occur as long as the root cause is not found. Besides the thyroid, the other class of adaptive hormones often imbalanced in stress-related diseases is the group of hormones mainly produced by the gonads: the sex hormones."

– Generative Energy – Restoring The Wholeness Of Life

Thyroid as the main regulator of respiratory adaptation

"The thyroid is the most important regulatory and adaptive substance for respiration."

– Email response from Ray Peat

Immunity: Innate vs. Adaptive in organisms

"In the 1960s, when antibodies were intensively studied, Metchnikoff's approach was called innate immunity, something more primitive and undifferentiated than the evolutionarily advanced adaptive immunity of B and T cells, bone and thymus cells. However, by then, an example of something similar to adaptive immunity, a learned response to a toxin, had already been demonstrated in plants."

– January 2020 – Ray Peats Newsletter

The role of inflammation in universal pathology

"Until the beginning of this century, inflammation was commonly seen as simply a constructive part of the local healing process, but it became recognized that it plays a universal role in pathology. Tissue damage was no longer considered merely a local event. Research was forced to reconsider Metchnikoff's holistic, developmental view of immunity. Bystander effects, the release of substances by any injured cell that induce similar injury in other cells, even in distant parts of the body (Koturbash, 2007; Kovalchuk, 2016), and the associated persistent epigenetic changes are part of innate immunity. This system is activated by adjuvants as well as the adaptive immune system that produces antibodies."

– January 2020 – Ray Peats Newsletter

Adaptive capacity of the organism in rich vs. poor environments

"In every situation, an adaptive metabolism takes place in the organism, and if the environment is unfavorable, the organism can defend itself by limiting its needs and range. However, if the environment is rich and needs are easily satisfied, the organism will tend to expand its range and capabilities."

– January 2018 – Ray Peats Newsletter

Tracking long-term effects of early childhood hypoglycemia

"If hypoglycemia occurs during pregnancy or infancy, when metabolic intensity is greatest, the adaptations can lead to lifelong problems."

– January 2017 – Ray Peats Newsletter

Extreme stress and biological adaptation: The balancing act of survival

"During adaptation, the functional load is shifted to the system facing the new challenge, and a variety of stimuli from nerves and hormones activate the cells of this responding system. Resources such as amino acids can be withdrawn from less active systems to support the new functional level. The organism must precisely focus its stimulation factors, and resources, including glucose stored as glycogen in tissues, must be sufficient. If the stimulation is too intense or too widespread and if too much fat is mobilized relative to glucose, self-destructive processes can occur."

– January 2017 – Ray Peats Newsletter

Adaptation effects on lactic acid formation and muscle performance

"Adaptation to hypoxia or increased carbon dioxide limits the formation of lactic acid. Muscles are about 50% more efficient in the adapted state; glucose, which produces more carbon dioxide than fat during oxidation, is metabolized more efficiently than fats and requires less oxygen."

– July 2000

Adaptive reactivity of organisms and homeostasis in cellular metabolism

"It is the subtle reactivity of the living system that maintains the adaptive organization of energy and structure. Part of the organism's reactivity is the flexibly interactive metabolism that adaptively distributes substance and energy. Ordinary metabolism can explain the processes called homeostatic more rationally by adjusting the affinities of cellular substance than the hypothetical devices of pumps and channels proposed in biology as deus ex machina whenever needed."

– December 1999 – Ray Peats Newsletter

Imperfection and adaptive capacity of organisms under stress

"Shock, inflammation, aging, and death have been proposed as survival values due to this totalitarian view of genetics. Could it be that organisms are simply not perfect and that some things just systematically go wrong? That is, an organism has a certain strength, resilience, or adaptive capacity, but when it finds itself in conditions that are too difficult, processes may arise that have never contributed to survival, as several individually valid defense maneuvers begin to interfere with each other."

– 1998 – Ray Peats Newsletter – 4

Essential role of breathing in higher organisms

"Breathing is essential for the existence of higher organisms because it enables the maintenance of complex and adaptive structures that contain correspondingly differentiated cells."

– 1998 – Ray Peats Newsletter – 3

Role of oxygen in cell acidification and edema regulation

"Oxygen, which produces carbon dioxide, makes the cell acidic, and carbon dioxide influences the handling of water by the cells. Carbonic anhydrase inhibitors are commonly used to regulate conditions with edema, including adaptation to high altitudes."

– 1998 – Ray Peats Newsletter – 2

Cell damage, repair, and adaptive responses in the organism

"If a cell has been damaged (e.g., by radiation or toxins), its inefficiency creates a small localized distortion in the fields that stimulates repair or removal and replacement processes, as far as the organism's resources allow. If stress is so great that the entire organism is exposed to lactic acid, the organism's adaptive resources are challenged, and potentially harmful reactions are triggered. For example, a sluggish liver during stress may allow an increase in blood lactate concentration, which can lead to the secretion of endorphins and pituitary hormones (Elias et al., 1997). Endorphins can increase histamine release, and growth hormone increases free fatty acids; increased permeability of blood vessels can allow proteins and fats to leave the bloodstream, with cumulatively harmful effects."

– 1998 – Ray Peats Newsletter – 2

Interlocking features of cell excitation and energy in stress adaptation

"The interlocking fundamental features of cell excitation/relaxation, electrical potential, lactic acid/carbon dioxide, water retention/water loss, salt regulation, pH, and energy level allow us to coherently visualize the biological significance of stress and adaptation. In interaction with these physicochemical events, there are many levels of biochemical and physiological processes that amplify or modify them, including regulatory systems such as hormones and other biological signaling substances, nutritional adequacy, and the type of fuel used."

– 1998 – Ray Peats Newsletter – 2

Respiratory potential and its effect on tissue changes

"A weakened ability to produce energy oxidatively can lead to maladaptive overproduction of collagen, porphyrins, red blood cells, and other tissues and substances, which in turn can trigger many adaptive and maladaptive changes. I think skin and mucous membranes provide a good illustration of how respiratory potential influences structure: The keratinization enhanced by estrogen is counteracted by vitamin A, which increases the proportion of active, differentiated cells."

– 1997 – Ray Peats Newsletter

The brain as the primary organ of cost-free adaptation

"As Felix Meerson has shown, the brain is the preferred organ of adaptation because adaptation at the level of learning has no biological cost in terms of limiting our structure and function."