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Allostatic load is the amount of metabolic energy needed for a given physiological mechanism to maintain its balance

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The amount of metabolic energy necessary for a given physiological mechanism to maintain its balance is called the allostatic charge. This term was conceived by McEwen and Stellar in 1993. When the body expends more energy than it should to reverse the stimulus that disrupted its balance, an allostatic overload occurs in some body's defense mechanism, increasing the risk of disease.

Homeostasis and Allostasis Processes

The term “homeostasis” indicates the property of an organism to remain in balance, regardless of changes and stimuli that occur in the external environment. Homeostasis is ensured through certain physiological mechanisms, which occur in organisms in a coordinated manner. The term “alostasis”, in turn, characterizes the mechanisms and tools that guarantee the establishment and maintenance of homeostasis.

The mechanisms that control body temperature, pH, volume of body fluids, blood pressure, heart rate and concentration of elements in the blood are the main allostatic tools used to maintain an organism's balance. These instruments work through a negative feedback, which guarantees an opposite change in relation to the initial change, that is, it produces responses that reduce the initial stimulus. Thus, he is responsible for ensuring the proper balance for the body.

• Learn more in the articles "What is homeostasis?" and "What is allostasis?"

stress response

A physiological response always occurs in response to a stimulus that disrupts homeostasis. Thus, an action on the individual, whether psychological or physical, will have as a response the deviation of homeostasis and a consequent allostatic reaction to regain balance. Stress is an example of a common stimulus in the daily lives of individuals and corresponds to a real or imaginary event that threatens homeostasis, requiring an allostatic response from the organism.

According to the Allostatic Charge Theory (ACT) developed by McEwen and Stellar, response expectations to a stimulus can be positive, negative or neutral. When the answers are positive and end a cycle of aggression, returning to homeostasis, the individual's health is not put at risk. On the other hand, when the allostatic charge is maintained for long periods or the adaptive response that would end the cycle of aggression does not occur, we have allostatic overload and the consequent damage to health.

The body's poor adaptation in an allostatic overload situation can cause damage to several organs, including the brain. This damage can manifest itself in different ways, against the background of tissue loss (degeneration), hypersensitivity, functional overload (hypertension) or psychological disorders (anxiety, depression). Daily stresses can be related to the onset or worsening of symptoms caused by this damage.

According to the book "Developmental Neuropsychology", the cascade of molecular and neurobiological effects associated with vulnerable situations in the environment, such as the neglect experienced by some poor children, may be an example of an allostatic response that would precipitate the allostatic charge in an organism still in its development. It has been shown that individuals with lower socioeconomic status report greater exposure to stressful events and the effect of these events on their lives than individuals with higher purchasing power.

This suggests that poor individuals can develop high vulnerability to stress and, consequently, to diseases or cognitive development difficulties. In a literature review, evidence was found that groups with experience of early stress present impairments in functions such as attention, language and decision-making, as well as alterations in brain components.