How Mitochondria Control Your Metabolism: Energy, Growth, Aging, and Disease

Most of us hear “metabolism” and think about calories in, calories out, or how easily we gain or lose weight. We hear “mitochondria” and remember one phrase from biology class: the powerhouse of the cell.

Neither description is wrong. But both leave out some of the most interesting biology.

Your metabolism is not one process running at a single speed. It is the combined activity of roughly 30 trillion cells, each taking in nutrients, transforming molecules, and allocating resources to its particular job. And mitochondria do much more than extract energy from food. They help determine whether those resources support immediate work, cellular maintenance, growth, or the production of another cell.

In my discussion with biochemist Dr. Jared Rutter, one idea kept coming into focus: health depends not simply on having energy, but on allocating resources appropriately. That distinction provides a powerful way to understand everything from a beating heart to cancer, aging, and the consequences of excess fuel.

Table of Contents

• Your Metabolism Is a Constellation of Cellular Metabolisms
• Why Mitochondria Are Far More Than Powerhouses
• Different Cells Need Different Mitochondria
• How Hormones Coordinate the Distribution of Fuel
• From Glucose to Pyruvate: A Crucial Metabolic Crossroads
• The Mitochondrial Pyruvate Carrier: A Small Gateway With Large Consequences
• What Happens When a Cell Allocates Resources Incorrectly?
• Fasting Reveals the Body’s Metabolic Flexibility
• Lactate Is a Fuel and a Shuttle, Not Simply Waste
• Cancer, Evolution, and the Warburg Effect
• Why Treating Cancer Requires More Than Blocking Growth
• Can We Measure Metabolic Health Inside Individual Cells?
• Excess Energy, Reactive Oxygen Species, and Aging
• A Better Framework for Understanding Metabolism

Your Metabolism Is a Constellation of Cellular Metabolisms

Think of cellular metabolism as a map. Nutrients enter at different points. Chemical reactions connect those entry points to many possible destinations.

A glucose molecule, for example, can be modified through a series of reactions that help a cell make usable energy. But parts of that same metabolic network also supply the materials needed to build proteins, membranes, and DNA.

At the whole-body level, we eat, drink, and breathe. Our bodies process those inputs, distribute their components, and eliminate waste. But the actual transformations happen within individual cells.

That means the important questions are not just “How many calories did I consume?” or “What is my metabolic rate?” They also include:

• Which cells take up which nutrients?
• What do those cells do with the nutrients they receive?
• How do they adjust when food becomes available or scarce?
• What happens when their resource allocation no longer serves their normal function?

A heart muscle cell and an intestinal stem cell live in the same body. Yet their metabolic priorities are profoundly different. Understanding those differences is essential to understanding metabolism itself.

Why Mitochondria Are Far More Than Powerhouses

An ancient partnership that enabled complex life

The leading explanation for the origin of mitochondria is extraordinary: a free-living bacterium entered another cell, and the two established a lasting partnership.

Rather than remaining independent organisms, they became integrated. That partnership helped enable the evolution of eukaryotic cells, the type of cells that make up animals, plants, and fungi.

We cannot reconstruct every detail of that original event or know precisely how each partner benefited at each stage. But the fact that complex life emerged from cells with this history makes a compelling case that the partnership provided important advantages, including new metabolic capabilities.

This is not merely an interesting evolutionary story. Mitochondria still retain evidence of that bacterial ancestry.

A separate genome, inherited through the egg

Most of our DNA resides in the nucleus. Mitochondria sit outside the nucleus, in the cell’s cytoplasm, and contain a separate genome of their own.

Unlike the linear chromosomes in the nucleus, mitochondrial DNA is circular, another connection to bacterial ancestry. It encodes proteins essential to mitochondrial function.

Importantly, inheriting mitochondria is not the same as having an outside object inserted into a body cell and somehow passing that object to your children. Mitochondria are transmitted through the egg and then distributed as the developing embryo produces more cells.

Our mitochondrial genome is therefore inherited from our mothers. That inheritance pattern matters for understanding mitochondrial diseases. The National Human Genome Research Institute provides additional background on mitochondrial DNA.

Location matters inside a cell

The familiar drawing of a cell as a round bag with a few structures floating inside is useful, but incomplete. Many cells have long extensions or highly specialized shapes.

Some neurons, for instance, send projections over enormous distances relative to the size of their cell bodies. Mitochondria travel along those projections and help supply energy where nerve terminals need it.

A moving immune cell offers another example. Crawling requires substantial energy, and mitochondria can redistribute toward the cell’s leading edge, close to where that energy is being consumed.

Energy production is not just about how much a cell can make. It is also about making it in the right place.

Different Cells Need Different Mitochondria

A heart muscle cell, or cardiomyocyte, has an unusually demanding assignment: contract repeatedly, every minute of every day, for a lifetime.

Those cells have very little turnover. Their mitochondria are strongly organized around extracting energy from available fuels and producing ATP, or adenosine triphosphate, the energy currency used throughout the body.

Now consider the stem cells that replenish the intestinal lining. Much of that lining turns over within roughly five to seven days. These stem cells must help generate replacement cells continually.

That requires more than ATP. Producing a new cell means producing:

• A new copy of its DNA.
• Proteins that carry out cellular functions.
• Lipids and membranes that create cellular boundaries and internal structures.
• The many other molecules needed to assemble a functioning cell.

Their mitochondria therefore support a metabolic program with much greater emphasis on biosynthesis, the production of biological material.

Even within a single cell, mitochondria may not all perform the same role. Rutter pointed to work from Craig Thompson and colleagues showing distinct mitochondrial populations within one cell, with one population more oriented toward biosynthetic functions and another toward energy extraction.

That is a major expansion of the powerhouse concept. Mitochondria are not interchangeable batteries. Their activities can be adapted to the particular demands of a cell, and potentially to different demands within that same cell.

How Hormones Coordinate the Distribution of Fuel

If every cell is making its own metabolic decisions, how does the body avoid chaos?

One answer is hormonal communication.

After a meal, digestion releases sugars, amino acids, and fats. Signals such as insulin and GLP-1 help communicate that nutrients have arrived. But different cells interpret those signals differently.

A fat cell responds to insulin by increasing glucose uptake and supporting energy storage. Through a sequence of reactions, nutrients can be converted into fat and stored for future use.

That storage function is not inherently a problem. It is an essential adaptation. Our ancestors could not count on regular meals, and stored fat helped sustain them through periods without food.

Other tissues respond to the fed state according to their own responsibilities. Some substantially change their metabolism. Others continue much as before.

This is why it is useful to think of insulin as more than a shuttle for glucose. It is information about the state of the organism. A cell’s response depends on both the signal and the job that cell needs to perform.

Cells also monitor their own resources

Hormones provide body-wide information, but cells also respond to their internal conditions.

When ATP availability falls, cells can reduce energy-consuming processes and activate pathways that help restore energy production. Similar feedback applies to other important metabolic products, including the building blocks of proteins and nucleic acids.

The system is not a fixed valve that always sends 90% of resources toward energy and 10% toward maintenance. Allocation changes in response to demand and supply.

When we say that a cell “knows” what it needs, we are using shorthand for this biochemical sensing and feedback. The cell is not thinking. But its responses can display remarkable adaptive logic.

From Glucose to Pyruvate: A Crucial Metabolic Crossroads

To understand resource allocation, it helps to follow glucose a little way into the cell.

1. Glucose enters the cell. It is a six-carbon sugar and an important fuel for many tissues.
2. Glycolysis modifies it through a sequence of reactions. This pathway produces pyruvate and captures some usable energy.
3. Pyruvate reaches a major branch point. It can enter mitochondria for further metabolism or follow other routes, including conversion to lactate.

When pyruvate enters mitochondria and is oxidized, the cell can extract much more of the energy originally present in glucose. Oxygen is essential to the mitochondrial machinery that supports this efficient ATP production.

But extracting the maximum amount of energy is not always the cell’s main objective. A growing or dividing cell also needs to preserve and redirect resources into the materials required for construction.

The analogy I find useful is a delivery of lumber. You can use the wood to build a house, or burn it to provide heat. And, of course, you need some energy to keep the construction project going.

That last point matters. Building and burning are not mutually exclusive. Every living cell needs energy, and every living cell needs some maintenance. The question is how resources are balanced across those demands.

An activated antibody-producing immune cell illustrates the construction side. Antibodies are proteins. Making large quantities of them requires amino acids, energy, and a metabolic system capable of supporting that production.

For a heart muscle cell, the immediate priority is different: keep generating enough ATP to sustain contraction while maintaining the machinery that makes contraction possible.

The Mitochondrial Pyruvate Carrier: A Small Gateway With Large Consequences

Pyruvate cannot simply pass freely through every mitochondrial barrier. It needs a transport mechanism.

That mechanism is the mitochondrial pyruvate carrier, or MPC, which includes the proteins MPC1 and MPC2. The name is refreshingly informative: it carries pyruvate into mitochondria.

Researchers had known for decades that such transport must occur. What they did not know was which proteins performed it.

Rutter’s laboratory became interested in mitochondrial proteins whose existence was established but whose functions remained unknown. Two of those proteins turned out to be MPC1 and MPC2.

How researchers discovered what MPC does

The discovery depended heavily on genetics.

Working with Carl Thummel’s laboratory, the researchers studied what happened when the relevant genes were removed in different experimental systems, including yeast, fruit flies, and human cells grown in culture.

Sophisticated chemical measurements revealed a consistent problem: metabolism was being interrupted at the step where pyruvate should enter mitochondria.

That observation suggested a hypothesis. Perhaps these proteins were the missing carrier. Further experiments tested and supported that explanation, and other laboratories subsequently validated the transport function.

The work developed over several years, beginning around 2008 or 2009 and leading to publication in 2012. A team led by Jean-Claude Martinou independently reported the discovery at the same time.

There is an important lesson here about how science works. Knowing a protein exists is not the same as knowing what it does. And no single experimental organism supplied the complete answer.

Yeast and flies offer short generation times and powerful genetic tools. Human cells provide another essential perspective. Putting those results together allowed the researchers to identify a pattern that would have been much harder to recognize in any one system alone.

Related work and publications are available through the Rutter laboratory’s publication list.

What Happens When a Cell Allocates Resources Incorrectly?

Removing MPC throughout a developing mouse prevents survival to birth. But genetic tools also allow researchers to remove it selectively from particular tissues, revealing how different cells depend on the same pathway.

The heart provides an especially revealing example.

When MPC is removed from heart muscle cells, the animals do not immediately die. Their hearts can still burn other fuels, including fats, to generate ATP.

Over time, however, the hearts become enlarged and the animals develop heart failure.

Rutter emphasized that the explanation is still being worked out. But the evidence suggests that the central problem is not simply an inability to make ATP. Instead, preventing normal mitochondrial pyruvate entry appears to redirect resources toward producing more cellular material.

The heart muscle cells grow, and that growth becomes structurally harmful.

A cell can have access to energy and still become unhealthy because it uses its resources in the wrong way.

This raises a potentially important therapeutic question: if a disease involves inappropriate metabolic allocation, could a treatment redirect resources toward a healthier balance?

That is an active research frontier, not an established instruction to manipulate MPC yourself. The same intervention could have very different consequences in different tissues.

Cell identity includes what a cell does

We often think of cell identity in terms of genes: this is a heart cell, this is a skin cell, this is an immune cell.

But function matters too. A heart cell that increasingly devotes resources to growth rather than supporting effective contraction is no longer carrying out its role appropriately, even if it remains recognizably a heart cell.

The same broad problem appears in other settings. Cancer cells direct resources toward excessive proliferation. Overactivated immune cells can support inflammatory disease.

This does not mean growth is bad. Intestinal renewal, tissue repair, and antibody production all depend on it. The issue is whether growth fits the cell’s function and the organism’s needs.

We also considered broader comparisons involving body size, growth signaling, and longevity, including the familiar difference between large and small dog breeds. Those comparisons are thought-provoking, but they are not proof of a universal rule that smaller cells, smaller bodies, or less growth always mean better health.

Fasting Reveals the Body’s Metabolic Flexibility

When food is unavailable, the body must shift from storing nutrients to mobilizing them.

Fasting-associated hormonal changes, including increased glucagon relative to insulin, help coordinate this transition. Stored fuels become available to tissues that need them.

The heart is particularly reassuring in this respect. It can use a remarkably broad range of fuels:

• Fatty acids.
• Glucose.
• Lactate.
• Ketones.
• Some amino acids.

Rutter described the heart as an omnivore. That flexibility helps it continue beating across different nutritional states. Fatty acids commonly supply a large fraction of its energy, including outside prolonged fasting.

The brain presents a different challenge. Neurons rely heavily on glucose, and their ability to use fatty acids directly is limited. Ketones provide an alternative fuel under appropriate conditions, but maintaining adequate blood glucose remains essential.

The contrast between high and low blood glucose is important. Persistently elevated glucose can cause serious damage over time. Severely low glucose can become dangerous very quickly.

So, once again, the body is not distributing one interchangeable fuel to identical cells. It is coordinating tissues with different abilities, priorities, and vulnerabilities.

Lactate Is a Fuel and a Shuttle, Not Simply Waste

Lactate is often discussed only in the context of hard exercise. But its role in metabolism is much broader.

One major fate of pyruvate is conversion to lactate, which can then leave the cell. This route is important when mitochondrial oxidation cannot meet the cell’s needs, including when oxygen availability is limited.

But lactate production is not restricted to oxygen-starved cells. It also fits into metabolic programs that support rapid growth and biosynthesis.

The key correction to the old waste-product story is that lactate still contains usable energy. Other cells can take it up and oxidize it. The heart is particularly capable of doing so.

Rutter highlighted work by Joshua Rabinowitz and others showing how important lactate can be as a circulating fuel. A molecule released by one tissue can become a resource for another.

We also discussed research connecting exercise-associated lactate signaling with brain-derived neurotrophic factor, or BDNF, which supports aspects of neural plasticity. That adds another dimension to lactate beyond fuel transfer.

The larger lesson is worth remembering: calling a molecule “waste” can close off questions we should still be asking. The same problem occurs when we reduce mitochondria to ATP generators.

Fuel use also reflects the need to prevent toxicity

There is no single, universal fuel priority list for every cell in every condition.

However, Rutter noted that excess free fatty acids can become acutely disruptive to cells. Dealing with them appropriately, including by oxidation, can therefore take priority.

Lactate also needs to remain within a regulated range. Its usefulness as a fuel does not mean that unlimited accumulation is harmless. Severe lactate accumulation and associated disturbances in acid-base balance can be dangerous.

Useful molecules still require regulation. That principle applies repeatedly across metabolism.

Cancer, Evolution, and the Warburg Effect

Cancer makes the resource allocation problem especially clear. A cancer cell increasingly uses the body’s resources to make more cancer cells rather than perform its original role.

Mutations are central to that process. Different mutations can help a cell proliferate, avoid cell death, evade immune surveillance, or tolerate damage that would otherwise limit its survival.

As those cells multiply, selection occurs within the tumor. Cells with traits that help them survive and reproduce under local conditions can become more abundant.

Why cancer does not behave exactly like a virus

Viruses face evolutionary pressure to spread between hosts. Some viral traits therefore help maintain a host long enough for transmission, or influence behavior in ways that facilitate spread.

Most cancers face a different situation. Their evolution is largely confined to the individual in whom they arise. A cancer cell can gain a competitive advantage within that body without gaining any advantage from preserving the body over the long term.

Rare transmissible animal cancers, such as those affecting Tasmanian devils, are notable exceptions, not the usual model of human cancer.

None of this requires a virus, bacterium, or cancer cell to think. Mutation and selection can generate behavior that looks strategically organized without conscious planning.

The same evolutionary framework applies to the microbiome. Microbes compete and propagate within their environments, including our bodies. The provocative idea that humans are simply vehicles for microbial dispersal is a philosophical framing, not an established explanation of human behavior. What is clear is that the relationship between host and microbes is biologically consequential.

What the Warburg effect does and does not mean

Otto Warburg’s work drew attention to the unusual metabolism of cancer cells. Many rely heavily on glycolysis and lactate production rather than oxidizing as much fuel as one might expect, even when oxygen is available.

Warburg interpreted this as evidence that mitochondrial dysfunction was central to cancer.

But altered energy metabolism does not mean that cancer mitochondria are simply broken.

As Rutter explained, mitochondria in cancer cells can be highly functional, including in their support of biosynthesis. The cell needs the materials to duplicate itself, not merely the maximum ATP yield from every nutrient molecule.

The Warburg effect makes more sense when viewed through resource allocation: cancer cells must support construction as well as energy production.

This also helps explain the logic of FDG-PET imaging. FDG is a labeled glucose analogue that allows clinicians to detect areas of glucose uptake. Many tumors take up substantial amounts of glucose, making that uptake useful for identifying disease.

It does not follow that all cancers have identical metabolism or that one dietary change can selectively deprive every tumor of fuel.

Why Treating Cancer Requires More Than Blocking Growth

There are two major obstacles to effective cancer treatment.

1. Cancer uses machinery that healthy cells also need

A bacterium is recognizably foreign. A cancer cell is one of our own cells, altered.

Many cancer capabilities are exaggerated or redirected versions of normal cellular functions. Healthy stem cells also divide. Immune cells also activate growth programs. The gut lining also needs continual replacement.

A treatment that attacks a shared process can therefore injure healthy tissues along with the tumor. This helps explain why therapies directed at proliferating cells can affect the gut and hair follicles.

Immunotherapies offer another route. Checkpoint inhibitors can interfere with mechanisms that tumors use to suppress immune responses, allowing immune cells to attack more effectively. They have produced remarkable results in some settings, but do not work equally well for every cancer. The National Cancer Institute explains the underlying approach in its overview of immune checkpoint inhibitors.

2. Tumors can evolve resistance

Imagine a drug eliminates 99.9% of a tumor’s cells. That sounds extraordinarily effective. But if the surviving fraction can reproduce, the tumor may return.

Those survivors may carry mutations or adaptations that make them resistant to the original treatment. The returning tumor is then harder to treat with the same drug.

This is why Rutter sees such promise in carefully chosen combinations of therapies. HIV treatment provides a useful analogy: targeting several vulnerabilities at once makes simultaneous resistance more difficult.

For cancer, the goal is to identify combinations that exploit a particular tumor’s vulnerabilities while limiting harm to normal tissues.

Drugs directed at specific cancer-associated mutations, including certain KRAS mutations, illustrate the potential of increasingly precise targeting. But even targeted therapies can encounter resistance, reinforcing the importance of combinations.

Tumor biology matters beyond its location

We classify cancers by where they occur: breast, liver, colon, and so on. Location remains important, but it does not fully describe the disease.

Some tumors from different organs may share more relevant biological features than two tumors from the same organ.

A more complete picture includes:

• The mutations that help drive the tumor.
• The pathways that sustain its survival and proliferation.
• The mechanisms it uses to evade immune attack.
• The metabolic processes that supply its building materials.

We discussed David Fajgenbaum’s work on drug repurposing as an example of the broader effort to match existing treatments to specific disease biology, including through computational approaches and experimental testing.

The encouraging idea is not one miracle drug for every cancer. It is a better-matched combination for a particular patient’s disease.

Metabolism is part of that picture, but it is not an easy shortcut. A tumor may rewire its pathways to make the same essential material by another route. Blocking one route can create pressure to find an alternative.

Can We Measure Metabolic Health Inside Individual Cells?

A compelling future would be one in which we could map a tissue’s metabolism, identify an unhealthy allocation pattern early, and safely shift it back toward normal.

Conceptually, that is attractive. Technically, it is extremely difficult.

First, there is the resolution problem. Distinguishing individual cells deep inside a living human body is very different from examining cells in a dish.

Second, there is the measurement problem. Metabolism is not directly visible. Researchers need a measurable signal that reliably reflects the process they care about.

Third, there is the interpretation problem. Which measurement, or combination of measurements, distinguishes a healthy cell from an unhealthy one? The right answer may differ by tissue and circumstance.

Finally, the measurement must be safe enough to use without damaging the tissue being assessed.

Experimental tools are improving. Researchers can increasingly measure specific metabolites and metabolic activity at particular locations within cells. Those advances are already teaching us more about how resource allocation works.

But a comprehensive, noninvasive map of every cell’s metabolic health is not a clinical capability we currently have.

Could breath or scent reveal metabolic changes?

Reports of dogs detecting certain cancers and of a person recognizing an odor associated with Parkinson’s disease raise an intriguing question: could disease-related metabolism produce detectable chemical signatures?

The basic logic is plausible. Smells are chemicals. A change in metabolic activity can change which compounds a body produces and in what proportions.

Breath, like blood, can therefore contain information about internal chemistry.

The difficult work is moving from an interesting observation to a chemically specific, reliable diagnostic test. Researchers need to establish what is being detected, how consistently it tracks disease, and what else could produce the same signal.

These observations are research leads, not a reason to diagnose disease by smell.

Excess Energy, Reactive Oxygen Species, and Aging

We tend to associate health with having more energy. At the mitochondrial level, however, more is not always better.

Before energy extracted from food is captured in ATP, it helps power the mitochondrial machinery. If that system becomes excessively energized relative to demand, it can become more susceptible to producing reactive oxygen species.

These reactive forms of oxygen can damage proteins and nucleic acids, including DNA.

Rutter described this as a widely accepted, though not universal, hypothesis linking excess mitochondrial energy to cellular damage. It is one reason to take the idea of energy excess seriously beyond its effect on body weight.

Too much incoming fuel can create problems even before we consider how much fat is stored.

Aging adds another layer. Mitochondria commonly become less effective with age, and accumulated cellular damage is strongly associated with the aging process.

Experiments in model organisms support a contribution from that damage, but many causal details remain unresolved. Why particular damage accumulates, which changes matter most, and how best to prevent or reverse them are still active questions.

That uncertainty matters when we ask why children seem to have endless energy while older adults often do not. Mitochondrial changes are part of the picture, but there is no single, complete molecular explanation.

A Better Framework for Understanding Metabolism

The main shift is simple: stop thinking of metabolism as one dial labeled fast or slow.

Think instead of a coordinated network of cellular systems. Each cell must obtain appropriate nutrients, make enough ATP, maintain its structures, and grow or divide only when that supports its role.

Mitochondria help make those decisions possible. They support energy extraction, but they also support the production of the materials from which cells are built.

Too little fuel can be dangerous. Too much can be damaging. Growth can restore a tissue or undermine it. A pathway that is beneficial in one cell type can be harmful when redirected in another.

That is why understanding metabolism requires more than counting inputs and outputs. It requires asking what resources are being used for, where they are being used, and whether that use supports the health of the whole organism.

For a broader collection of science-based tools related to sleep, exercise, stress, focus, and motivation, my book Protocols: An Operating Manual for the Human Body brings those topics together with their scientific foundations.