Cancer as a Metabolic Disease: A Conversation on Mitochondria, Fermentation, and a New Direction for Cancer Care

For nearly a century, the dominant view of cancer has centered on genes. According to the somatic mutation theory, cancer begins when mutations inside the cell drive uncontrolled growth. This theory has shaped the direction of modern oncology, pharmaceutical research, and many of today’s cancer treatments.

But Professor Thomas N. Seyfried of Boston College believes the field has been looking in the wrong place.

In a recent conversation on The Moss Report with Dr. Ralph W. Moss and Ben Moss, Professor Seyfried laid out the case for a very different understanding of cancer: that it is primarily a mitochondrial metabolic disease, not a genetic one. In this view, genetic mutations are not the root cause of cancer. They are downstream effects of damage to cellular energy metabolism.

At the center of this theory is the mitochondrion — the energy-producing organelle inside the cell.

See the interview here:

https://www.youtube.com/watch?v=fvqCub79kaY

For the TLDL:

According to Seyfried, all major cancers show some type of defect in mitochondrial number, structure, or function. These defects impair the cell’s ability to generate energy efficiently through oxidative phosphorylation. When that system breaks down, cancer cells fall back on older, more primitive energy pathways: fermentation.

Revisiting Otto Warburg’s Discovery

The conversation began with Otto Warburg, the German biochemist who first proposed that cancer involved abnormal cellular respiration. Warburg observed that cancer cells often ferment glucose into lactic acid even in the presence of oxygen. This became known as the Warburg effect.

Warburg was awarded the Nobel Prize for his discovery of the respiratory enzyme cytochrome c, though not specifically for his cancer work. He was nominated many times for his research on cancer metabolism but never received the prize for that area.

Seyfried explained that Warburg understood something profound: cancer cells rely heavily on fermentation because their mitochondria are damaged. However, Warburg did not have all the information available today. Two key issues, Seyfried said, led the field away from Warburg’s metabolic theory and toward the genetic theory of cancer.

First, Warburg did not know that cancer cells could also ferment glutamine, not just glucose.

Second, he assumed that oxygen consumption was a reliable marker for ATP production through oxidative phosphorylation. Seyfried argues that this assumption is true for healthy cells but not for cancer cells.

Cancer cells may consume oxygen, but according to Seyfried, that oxygen is not primarily being used to make ATP. Instead, much of it is used to generate reactive oxygen species, which can damage DNA and contribute to the mutations seen in cancer cells.

In other words, cancer cells may still consume oxygen, but their energy metabolism remains impaired.

The Missing Fuel: Glutamine

Warburg focused on glucose fermentation and the production of lactic acid. Seyfried and his colleagues have expanded the picture by identifying glutamine as the second major fermentable fuel used by cancer cells.

Glutamine is the most abundant amino acid in the body. Cancer cells are well known to have a strong dependence on it, often described as “glutamine addiction.” But for years, Seyfried said, the mechanism was not fully understood.

His research suggests that cancer cells ferment glutamine inside the mitochondria through a process called mitochondrial substrate-level phosphorylation. This process allows the cancer cell to generate ATP even when oxidative phosphorylation is impaired.

The waste product of this glutamine fermentation is succinic acid, just as lactic acid is the waste product of glucose fermentation.

Seyfried described lactic acid and succinic acid as the “exhaust” of cancer metabolism. These acidic waste products contribute to the acidified tumor microenvironment, which can make cancer cells more resistant to conventional treatments such as chemotherapy, radiation, and immunotherapy.

The implication is significant: if cancer cells depend heavily on glucose and glutamine fermentation, then effective metabolic management of cancer must address both fuels at the same time.

Why Targeting Glucose Alone May Not Be Enough

Many people are familiar with ketogenic diets as a way to lower blood glucose and increase ketones. Seyfried supports the use of nutritional ketosis as part of a metabolic approach to cancer care, but he emphasizes that glucose restriction alone may not be sufficient.

If glucose is reduced, cancer cells may increase their dependence on glutamine. If glutamine metabolism is targeted without addressing glucose, the cancer cells may shift back toward glucose metabolism.

This is why Seyfried advocates a dual-targeting strategy: reduce glucose availability through nutritional ketosis while also strategically targeting glutamine metabolism.

Ketones and fatty acids can nourish healthy cells because healthy cells have functional mitochondria. Cancer cells, by contrast, are unable to effectively use ketones or fatty acids for energy because their mitochondria are damaged.

This creates a therapeutic window. The body can be supported by ketones while cancer cells are placed under metabolic stress.

The Glucose Ketone Index

Seyfried often refers to the glucose ketone index, or GKI, as a tool for measuring metabolic status. The GKI compares blood glucose to blood ketone levels and gives patients and practitioners a way to assess whether the body has entered a therapeutic state of nutritional ketosis.

A lower GKI suggests lower glucose availability and higher ketone availability. Seyfried believes this metabolic state can make cancer cells more vulnerable, especially when paired with therapies that target glutamine metabolism.

He also emphasized that exercise can help lower glucose and improve the GKI. Muscle activity pulls glucose out of the bloodstream, which can help people reach a more favorable metabolic state.

The Press-Pulse Strategy

Seyfried described his approach as a “press-pulse” therapeutic strategy.

The “press” refers to the ongoing pressure placed on cancer cells through nutritional ketosis and glucose restriction. The “pulse” refers to the strategic, intermittent use of therapies that target glutamine metabolism.

This pulsing is important because glutamine is also used by healthy tissues, including the gut and immune system. Too much glutamine inhibition could cause harm. Seyfried emphasized that dosage, timing, and scheduling must be carefully developed to maximize cancer cell vulnerability while minimizing collateral damage.

He discussed several compounds of interest, including DON, mebendazole, and fenbendazole. DON, also known as 6-diazo-5-oxo-L-norleucine, is described by Seyfried as a powerful glutamine-targeting drug. He also discussed antiparasitic medications such as mebendazole and fenbendazole, noting that these drugs may affect both glycolysis and glutaminolysis pathways.

Seyfried’s view is that these medications may work against cancer because parasites and cancer cells share certain primitive energy pathways, including mitochondrial substrate-level phosphorylation.

He stressed that these compounds should not be understood as stand-alone cures. In his model, they are most effective when used in the context of nutritional ketosis and careful metabolic management.

Making Conventional Treatments Less Toxic

One of the most compelling points in the conversation was Seyfried’s argument that metabolic therapy does not necessarily have to replace conventional treatments. Instead, it may make cancer cells more vulnerable to those treatments.

If glucose and glutamine are restricted, the tumor microenvironment may become less acidic and cancer cells may become weaker. In that vulnerable state, lower doses of chemotherapy, radiation, or other treatments may be more effective and less damaging to healthy tissue.

Seyfried suggested that many existing cancer drugs that were considered too toxic might be “rescued” if used in combination with nutritional ketosis and better metabolic timing.

The larger goal is not simply to attack cancer harder, but to attack it more intelligently — by exploiting the metabolic weaknesses of cancer cells while preserving the health of normal cells.

Why This Paradigm Has Been Slow to Gain Acceptance

A major theme of the conversation was the resistance that new ideas face when they challenge an established paradigm.

Seyfried compared the metabolic theory of cancer to other major scientific shifts, including the heliocentric model of the solar system, germ theory, and evolutionary theory. In each case, the new model met resistance because it disrupted existing institutions, beliefs, and careers.

He argued that the cancer field remains deeply committed to the genetic theory because funding, research programs, drug development, and academic careers have been built around it.

If cancer is primarily genetic, then the logical approach is to identify and target cancer-driving mutations. But Seyfried argues that decades of mutation-focused research have not produced the breakthrough that patients need.

In his words, the problem is not in the nucleus. It is in the mitochondria.

A Path Forward

Seyfried emphasized that the science behind the mitochondrial metabolic theory is strong, but the practical clinical application still needs refinement.

More work is needed to determine how best to implement metabolic therapies across different cancer types, ages, sexes, body compositions, diets, and individual patient needs. The timing and dosing of glutamine-targeting drugs must also be carefully studied.

He noted that his lab is supported by philanthropy and private foundations and that clinicians around the world are beginning to explore metabolic approaches. He also mentioned the formation of an international society focused on metabolic oncology.

The work ahead, he said, involves developing better protocols, collecting case data, testing strategies in preclinical models, and learning from clinicians and patients using these approaches in real-world settings.

A New Way to Understand Cancer

The metabolic theory of cancer asks us to see cancer not first as a disease of broken genes, but as a disease of broken energy metabolism.

In this model, mitochondrial dysfunction forces cells to rely on fermentation. Glucose and glutamine become the primary fuels driving uncontrolled growth. The waste products of fermentation acidify the tumor environment, making cancer more aggressive and harder to treat.

By transitioning the body into nutritional ketosis, reducing glucose availability, and strategically targeting glutamine metabolism, Seyfried believes cancer can be managed with less toxicity and greater precision.

This approach remains outside mainstream oncology, and anyone considering dietary or metabolic therapies for cancer should do so only with qualified medical guidance. Still, the conversation points toward a powerful possibility: that the future of cancer care may depend not only on targeting mutations, but on understanding and correcting the deeper metabolic conditions that allow cancer to thrive.

As Seyfried framed it, cancer may not be hundreds of different genetic diseases. It may be one disease with a common metabolic foundation.

And if that is true, the path forward could look very different from the one oncology has followed for the past several decades.