Doug Bonderud

May 5th 2021

Allostasis: Balancing the Books of Brain-Body Budgets


The human brain is remarkable. Even in uncertain times filled with significantly stressful events occurring at breakneck speed, our brains empower adaptation that allows us to survive — and even thrive. This robust resilience is governed by a process known as allostasis: the human brain’s ability to adjust as environmental conditions change by budgeting essential mental and physical resources. Here’s a look at how it works, why it matters and what impacts it can have over time.

Crunching the Numbers

Before allostasis comes homeostasis. Scientific American reports that the concept was first defined by physician Walter Cannon in the 1930s to describe any processes used by organisms to actively maintain stable conditions to facilitate continued existence. The term itself is a combination of two Greek words, “homeo” for same and “stasis” for state. This is the simple goal of any living thing — to find and maintain a steady state for survival.

While the goal of homeostasis is stability, we live in a world that’s anything but stable. To achieve some semblance of homeostasis, our brains have learned to budget the mental and physical effort we need to survive day to day and adjust this budget to meet evolving needs over time.

This budgeting benefit is known as allostasis — the process by which the brain achieves stability through change, as a study published in Psychology Review defines it. This enables the brain to seek out and create homeostasis, even when it’s not immediately available. In practice, allostasis allows humans to cope with the stress of daily life by continually adapting our mental and physical states to align with current conditions.

One common example of this is how the brain regulates body temperature, as points out. But an even more instructive example is the stress response, they note. If there’s a tiger in the room, your brain will use every resource your body has available, including making your blood pressure skyrocket, to get you back to somewhere where there can be homeostasis — and no tigers.

The Brain-Body Balancing Act

Allostasis is functionally adaptive, because this proactive preparation makes it easier to deal with environmental challenges such as the risk of predator attacks or food scarcity. Over time, human brains have become masters of allostatic alignment, helping our bodies navigate day-to-day tasks with relative ease.

Consider the simple act of drinking water. As a recent New York Times piece notes, it takes about 20 minutes for the impact of intake to reach our bloodstream — and yet relief from thirst happens almost instantaneously. This is part of the brain’s allostatic budgeting process. It’s learned over time that water consumption equals physical hydration, and so it provides the necessary, beneficial outcome of thirst quenching to help humans focus on other tasks rather than waiting.

In practice, this allostatic allotment process functions as a form of stress management, allowing our bodies to meet the needs of the moment while still keeping us on a (relatively) even keel. The caveat? Ongoing allostatic adjustments can have significant, long-term effects.

Stressed to Progress

We’ve all heard the term “stressed out” — but what exactly does it mean? We often connect stress to specific circumstances in our lives, such as moving to a new city, having kids or struggling with issues at work. But stress is often part of a larger, ongoing picture that contributes to ongoing allostatic load, in turn forcing our brains to continually rebudget and redistribute resources.

This issue is exacerbated by the continual influx of technology — from smartphones to social media to wearable devices. These all provide useful data, but they can also lead us down a rabbit-hole of mental stress as we dwell on the current state of the world, evolving work obligations or the state of our health. As intelligent, self-determining human beings, we can often recognize this stress for what it is: non-life-threatening but still worrisome. Meanwhile, our brain budgets have no such ability; their allostatic processes see all stress responses the same way.

According to an article in Psychology Today, this stress is a critical factor in physical illness, with 50% to 70% of all ailments linked in some way to stressful circumstances. But there’s an even bigger problem: allostatic overload.

Operational Overload

The cumulative impact of our brain’s stress budgeting is known as “allostatic load.” The higher the load, the more our brains are doing to solve for homeostatic stability and the greater our mental wear and tear. According to the Journal of Psychiatry and Neuroscience, under significant and prolonged stress, it’s possible to enter a state of allostatic overload, which occurs when “acute responses are overused or inefficiently managed.” As the Psychology Today article notes, these stress conditions are cumulative. The continual release of hormones and neurotransmitters to mitigate stress can negatively affect everything from immune system function to metabolic processes and cardiovascular operation.

Consider our late-night early-morning example from above. Your brain can rebalance after the occasional lack of sleep, and a few days of better rest can help get you back on track — but continually staying up until 2 a.m. and then forcing yourself out of bed each morning causes an ongoing allostatic reaction which eventually becomes the baseline for your brain. Over time, this allostatic overload reduces the efficacy of existing stress-control measures and makes it harder to achieve homeostasis, in turn promoting even more mental effort, leading to a vicious cycle of stress and response that’s cumulative over time.

Put simply? Our resistance is remarkable — but it comes with a cost. While evolutionarily adaptive, the mental withdrawals made by allostatic brain budgeting must occasionally be balanced by deposits of stress-reducing strategies, such as meditation, humor, exercise or cognitive reframing to help limit the long-term impacts of allostatic overload.