also occurs at the cellular and systems levels. When humans are chronically stressed, the brain chronically raises blood pressure; then arterial muscles predict higher pressure and respond with hypertrophy (like skeletal muscles when we lift weights). Gradually the whole cardiovascular system adapts to life at an elevated pressure level. This is known as chronic hypertension, which elevates mortality from cardiovascular disease and stroke. Similarly, a chronically high carbohydrate diet requires chronically high blood glucose and leads to chronically high levels of insulin that increase in anticipation of the need to manage the high level of carbohydrates. Cells that express insulin receptors, predicting high insulin, adapt by reducing their sensitivity (like photoreceptors in bright light). This leads to type 2 diabetes and elevated mortality from many causes. Although physicians term this response insulin resistance, it can be better understood as consequent to predictive regulation. Every system evolves to operate over a particular range. For example, cone photoreceptors evolved to sense daylight over a 10,000-fold range of intensities, whereas rod photoreceptors evolved a different design to sense moonlight and starlight down to detection of single photons. To function optimally across their wide operating ranges, all systems adapt their sensitivities. A rod photoreceptor adapts to bright moonlight and requires minutes to increase its sensitivity to starlight. When a system is chronically forced beyond its intended operating range—as by chronic high carbohydrate diet or other stress—the limits of adaptation are exceeded, and systems break down. This condition was termed by Bruce McEwen as allostatic load. The health of an organism is maintained when operating within certain parameters, but having dynamic variability of range. Too much allostasis, also known as allostatic “overload” can lead to various negative consequences as American Addiction Centers write, “The cost of adapting to external conditions becomes so high that it causes mental or physical disease." From a metaphorical perspective this can be interpreted as a machine running continuously as the machine is overworked; it becomes less efficient over time because more stress is placed on it. Similarly, the process of allostasis becomes less efficient at managing the body's resources when the body endures increased levels of unhealthy stress due to wear and tear on the body and the brain. An increase in Allostatic load can impair and reduce neuroplasticity as stress causes the brain to age quicker. This is because with more stress, more synaptic connections are lost in the