Abstract
The reactivity of the stress system may change during the life course. In many—but not all—humans the stress reactivity decreases, once the individual is chronically exposed to a stressful and unsafe environment (e.g., poverty, work with high demands, unhappy martial relationship). Such an adaptation is referred to as habituation. Stress habituation allows alleviating the burden of chronic stress, particularly cardiovascular morbidity and mortality. Interestingly, two recent experiments demonstrated low stress reactivity during a mental or psychosocial challenge in subjects with a high body mass. In this focused review we attempt to integrate these experimental findings in a larger context. Are these data compatible with data sets showing a prolonged life expectancy in corpulent people? From the perspective of neuroenergetics, we here raise the question whether “obesity” is unhealthy at all. Is the corpulent phenotype possibly the result of “adaptive phenotypic plasticity” allowing optimized survival in stressful environments?
Highlights
The reactivity of the stress system may change during the life course
Our findings suggest that the absence of Cerebral insulin suppression (CIS) in corpulent subjects was due to the absence of their meal-related-cortisol peak
THE ALLOSTATIC LOAD IS LOW IN THE CORPULENT PHENOTYPE When comparing the health risks of chronically stressed type-A and type-B-individuals we find strong evidence for several differences that are summarized in Table 2: while A-types remain high-reactive in their stress reactivity, B-types habituate and develop a lowreactive stress system
Summary
The Obesity Paradox The term reflects the controversy which arose from conflicting study results: while some studies reported negative associations between body mass and mortality risk, others reported positive associations between the two variables. CIS can be interpreted as a brain-pull mechanism that functions to demand energy from the body. In this way, the brain is able to adjust its energy supply to its varying energy needs. By activating brain-pull mechanisms the brain demands for extra energy from the body and thereby covers such cerebral extra needs. Once exposed to a stressful environment (e.g., poverty, unhappy martial relationship, high demand at work, loneliness), humans are known to react in two distinct patterns (Kirschbaum et al, 1995): type-A-individuals are characterized by their maintenance of a high-reactive stress response under conditions of permanent or repeated stress They do not show any signs of habituation.
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