Energy Constraint on Health
How Ongoing Energy Competition Within Your Body Shapes Your Health
ENERGY SCIENCE
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Ever since we found that hair graying is (temporarily) reversible and seemed to emerge from energy competition, we tried to understand why and how energy could limit and constrain our ability to be healthy.
Five years of work has just come to fruition.
Seeing the final PDF with our paper published just last week felt pretty special. The final paper is fairly lengthy, but it boils down to one fundamental concept:
We have a fixed energy budget that is dynamically, competitively reallocated between the cells, organs, and systems across our bodies.
This concept was developed with Alexander Behnke, Evan Shaulson, Herman Pontzer, Chris Kempes, co-authors on this paper. Together, we’ve integrate work from wide-ranging fields ranging including molecular and cell biology to exercise physiology, psychobiology, human energetics, and clinical medicine.
The bottomline is that everything we do costs energy. And that how we manage our energy budget likely plays an important role in health and disease.
Here’s how we think this works:
Our Bodies Expend Energy at Different Scales
When we talk about energy expenditure, you may immediately think of costs related to behaviors like physical activity and exercise. Things that make you breathe harder do, indeed, cost more energy.
What you may not think about as often are all of the other nested processes at the intracellular (within-cell) and intercellular (between-cell) levels: the stuff inside and between your cells.
Everything costs energy. Nothing is free in biology.
For example, when genetic information from your DNA is transcribed and translated to synthesize a protein, it costs energy. When one of your cells releases a signaling molecule—a cytokine—for other nearby cells, it also costs energy. And when a neuron fires, or your immune system activates to fight off an infection, that, too, costs energy.
All molecular, cellular, physiological, and behavioral processes add up to your whole-body energy expenditure.
Why We Don’t Have Unlimited Energy
But why do we have to live life on a budget? If we want to have “more energy,” why can’t we just eat more?
Our bodies have evolved to have limits. There are limits to the amount of energy that our metabolism, including our mitochondria, can transform. Limits to how much food our gut can digest. And limits, at least in mice, to how well energy can be dissipated as heat, within a given amount of time.
Breathing in more oxygen or consuming more food don’t get us around these fundamental limits.
Time is an important factor to consider.
Think about what happens in an intense sprint (the top left datapoint on the graph below). Your metabolic rate easily rises to a high level for a short period of time, but as the seconds tick by, you feel it. You have to slow down.
It’s not humanly, energetically possible to maintain that same level of energy expenditure for very long. It’s outside of the limits of our energy budget. We can only do high-intensity activities for short periods of time.
But if we keep the activity more moderate, we can run or walk at a moderate metabolic rate for hours, and still stay within the limits of our energy budget.
For short time periods, like a brief bout of intense exercise or an extremely stressful event, we can temporarily “exceed” our energy budget. That’s the blip up on the image below.
But if that excess energy expenditure continues over several weeks, our bodies start to make changes to compensate and bring energy usage back down to our baseline limit. That’s the idea of metabolic compensation, initially proposed by my colleague Herman Pontzer in 2016—a controversial idea, since then studied by many others.
Herman wrote a book on this, Burn. Great book, where he tells stories of going to Africa to study people who walk non-stop for the better part of day… yet expend the same amount of energy as a sedentary office worker living in New York City.
How does this work?
We won’t get into the details here. But briefly, energy compensation likely arises from increased efficiency: achieved by lowering our resting heart rate, or by prompting sleep—a state where energy expenditure decreases significantly from waking levels.
The body might also compensate and save energy by shutting down processes that aren’t essential for survival. Fascinating stuff that remain to be understood.
How Our Bodies Prioritize Energy Allocation
Our bodies are constantly making decisions about how our limited energy should be spent. To survive and thrive, our energy resources are dynamically reallocated to meet our energy needs on a daily and longer-term basis. This forces trade-offs across the different scales of energy expenditure.
But how do our bodies decide what to spend energy on at any given moment?
In our Energy Constraint (EC) paper, we propose that all of the processes in our bodies relevant to health can be roughly divided into three categories: vital; stress; and growth, maintenance, and repair.
The vital category includes life-sustaining costs that are essential to keep our systems running on short timescales (minutes to days).
The stress category covers any stimulus that results in an energy cost. These can range from beneficial stimuli like exercise or detrimental stimuli like exposure to a toxin.
The growth, maintenance, and repair (GMR) category encompasses all processes that are not required for survival on short timescales. However, these processes are longevity-promoting and necessary for survival in the long term.
These three categories can be arranged in a hierarchy where the more ‘urgent’ vital- and stress-related processes are prioritized by suppressing GMR processes. In other words, if there isn’t enough energy to cover all of your energy demands, GMR processes are sacrificed.
The inspiration for the “hierarchy of energy needs” pyramid above was the psychologist Abraham Maslow’s “hierarchy of human needs.”
Maslow proposed that humans must satisfy lower-level physiological and safety needs before they can pursue higher-level needs like belonging, esteem, and self-actualization.
Here, we propose that the human body similarly operates according to a hierarchy of energy needs, where more urgent vital functions and stress-related processes are prioritized over GMR processes when energy is limited.
A New Model of Health Based on Energy Constraint
We know that excessive energy expenditure (hypermetabolism) is not something that we can sustain indefinitely. Being in a state of chronic hypermetabolism can lead to the accumulation of damage, accelerated aging, and a shorter lifespan.
On the other hand, lower energy expenditure (hypometabolism) can slow aging and prolong lifespan. Animals who hibernate and go into severe hypometabolism even seem to stop aging.
The Energy Constraint model provides a framework to help explain how energy expenditure is related to health.
Over time, trade-offs that limit GMR have consequences for aging and health.
Since we can’t reallocate energy needed for vital processes, during periods of stress (hypermetabolism), less energy is available to be allocated to GMR
If the stressor is short in duration and low in intensity, then we can recover and address accumulated damage by temporarily expanding energy allocation to GMR afterwards.
With a more intense stressor, the disruption of GMR is more pronounced. That means more damage. And a longer recovery period that might not be able to fully reverse the damage already done.
Chronic Stress Impacts Energy Allocation
Some stressors in our lives resolve within a matter of minutes. These are called “acute.” But other stressors may continue to plague us for days, months, or even years. These are called “chronic.”
For short-term, acute stressors, your body can enter a temporary state of stress-induced hypermetabolism where GMR is reduced for a limited period of time (see below).
For chronic stressors, our model suggests that your hypermetabolic body begins to compensate to lower your energy budget back to baseline. GMR processes become chronically compressed, which drives more damage. And ff this state persists for weeks, months, or years, damage accumulates exponentially.
That’s basically aging.
Damage accumulation in aging cells increases the cost of sustaining vital processes. As a result, in aging cells, life becomes less efficient and more expensive.
The Energy Constraint model explains why aging is exponential. Because the more damage there is, the more costly vital processes become, the less energy there is for GMR. This compounding drives exponential damage accumulation.
Naturally, over the long-term, these changes in energy allocation then manifest as poor health.
Our Experiences Can Damage Our Health or Promote Resilience
Each individual goes through a unique series of life experiences. Our bodies respond to stressors and experiences by adjusting energy allocation.
Over time, your body’s energy trade-offs can impair or enhance your health.
Certain conditions like chronic psychosocial stress, infections, sepsis, and mitochondrial defects increase the allocation of energy for stress responses, reducing energy allocation to GMR. Life-threatening conditions like sepsis can even compress vital costs, leading to “vital” organ failure.
So the reason things like sepsis and metastatic cancer end up killing us could be because they rob the system of its energy budget, leaving no room for vital processes.
In contrast, we know that activities like sleep, intermittent fasting, exercise, and other well-being approaches promote resilience. We think these effects are driven by reducing vital costs, through improved efficiency.
Reducing stress through contemplative practices, for example, may also free up more of your energy budget for GMR.
What This Mean and Why This is Relevant for Your Life
The energy constraint framework helps us understand how energetic processes in our bodies can play a role in health and disease.
The EC model of health illustrates how, because of our limited energy budget, chronic stress can suppress the growth, maintenance, and repair (GMR) processes that help us heal and allow us to live long, healthy, and fulfilling lives.
For researchers, the framework identifies features that could be measured to better understand these processes and to develop treatments or preventative approaches to keep us healthy.
For us, this framework sparked a myriad of unanswered questions that we are excited to see the field investigate. How much energy does it actually cost to heal a wound? Or to recover from a psychological trauma? How quickly do energy compensations go into effect?
With this energy-based framework, we can start to answer these kinds of questions and gain a clearer picture of the dynamics of health and disease across our lifespan. Recognizing and studying the effects of energy constraint opens the door for us to leverage our knowledge of energy allocation to support and enhance health.
Curious about the mitochondria that support the energetic circuitry of the body and mind that drive energy constraints? Visit MitoLife to see what they look like.
The shift from a molecule-first view of biology to an energy-first one feels essential — and long overdue. If mitochondria are at the centre of health, then understanding how energy is produced, distributed, and used becomes the real question.
What I find myself exploring is what sits one level upstream of that.
Energy doesn’t allocate itself. The nervous system does.
And the nervous system is not operating in isolation — it is continuously reading the environment and adjusting energy allocation in real time. Light, sound, air quality, temperature, spatial cues, chemical exposures — these are not passive backdrops. They are inputs into the system that determines whether energy is directed toward repair, growth, or defence.
From that perspective, mitochondrial dysfunction may often be the downstream expression of a system that has been pushed, subtly but persistently, toward vigilance.
Not by a single acute stressor, but by a constant stream of low-grade, misaligned signals.
It raises a slightly different question:
not just how we support mitochondrial function,
but what environmental conditions allow the system to allocate energy well in the first place.
Feels like an important bridge between cellular energetics and the environments we inhabit every day.
As a patient who’s navigated illness for over a decade, I see this exact pattern playing out in my own health.. this has sparked so many questions for me as well!