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08 · Autophagy: Cellular Recycling, Fasting and Links to Cancer
Autophagy is a cell’s natural recycling system. It helps remove and reuse damaged or unnecessary cellular components. In cancer, however, its role is not straightforward.
In earlier stages, it may contribute to cellular stability. Established cancer cells can also use it to cope with nutrient shortages, hypoxia and other forms of metabolic stress.
What is autophagy?
Autophagy is a regulated process in which selected components of the cytoplasm are delivered to lysosomes, where they are broken down and their building blocks can be reused. It is a system for cellular quality control, recycling and metabolic adaptation.
Autophagy also occurs under normal conditions; it does not switch on simultaneously throughout the body after a fixed number of hours without food. The following description mainly concerns macroautophagy, the best-known form of autophagy. [1]
How does autophagy work?
A closer look: autophagic flux
Autophagy is more than the number of autophagosomes. What matters is the entire autophagic flux – autophagosome formation, cargo capture, fusion with a lysosome, degradation and recycling. This makes laboratory markers more difficult to interpret than they may initially appear.
Mitophagy: selective mitochondrial quality control
Mitophagy is a selective form of autophagy that targets mitochondria. It helps the cell maintain the quality of its mitochondrial network. Selective autophagy can also target other organelles and cellular structures.
Autophagy is not apoptosis
Autophagy
Recycles cellular components and often helps cells adapt to stress.
Apoptosis
A regulated programme that leads to the removal of an entire cell.
These processes can influence one another, but they are not interchangeable.
The paradox of autophagy in cancer
Experiments in cells and animals show that the significance of autophagy depends on the context. In one mouse study, disruption of the beclin 1 gene increased tumour incidence. Other experiments showed that cells with an activated RAS oncogene use autophagy to maintain metabolism and survive nutrient shortages. This does not demonstrate that promoting or blocking autophagy at home prevents cancer. [2, 3]
Early context
Maintaining protein and organelle quality may counter processes that promote tumour development.
Established tumour
Cancer cells may use autophagy to adapt to nutrient shortages, hypoxia and other stresses.
The outcome depends on the cell type, tumour stage, genetic context, microenvironment and treatment.
How can autophagy help an established tumour?
Cancer cells often grow in environments with fluctuating supplies of oxygen and nutrients. Under certain circumstances, recycling intracellular components can provide substrates for energy metabolism and biosynthesis.
A closer look: the microenvironment and immunity
Research examines autophagy not only in cancer cells but also in cells of the tumour microenvironment and the immune system. This is one reason why interventions affecting autophagy can produce different outcomes in different tumours.
Fasting, ketosis and autophagy: what do we know?
Nutrient shortages and energy stress can influence pathways that regulate autophagy. However, the number of hours since a person’s last meal does not precisely identify a moment when autophagy “switches on”.
The glucose–ketone index describes the relationship between glucose and ketones. By itself, it does not establish whether, or to what extent, autophagy is occurring in a particular tissue.
The mechanisms of autophagy do not establish fasting or a ketogenic diet as a stand-alone cancer treatment. Nutrition and the risk of malnutrition can be clinically important in people with cancer.
An exploratory analysis published in 2025 investigated changes in autophagic flux during intermittent time-restricted eating. It examined a specific regimen and the cells studied; it does not provide a universal timer for autophagy or evidence of a cancer treatment. [4]
If you have cancer, do not start fasting or substantially restrict food without discussing it with your care team. ESPEN guidance emphasises preventing malnutrition and does not recommend fasting around anticancer treatment because benefits are insufficiently established and nutritional risks remain. [5]
What have clinical trials shown?
Researchers have tried to influence autophagy using hydroxychloroquine alongside chemotherapy, for example. Findings have depended on both the outcome measured and the patient group studied. [6, 7]
| Research | Finding | Limits of interpretation |
|---|---|---|
| Advanced pancreatic cancer, randomised trial (2019) | Adding hydroxychloroquine to chemotherapy did not improve the primary outcome: overall survival at 12 months. | A higher tumour response rate did not demonstrate a survival benefit. [6] |
| Preoperative treatment of pancreatic cancer, randomised trial (2020) | The response assessed in tumour tissue after surgery improved. | No difference in overall survival or relapse-free survival was demonstrated between the groups. [7] |
These findings do not justify taking hydroxychloroquine or other medicines on your own to “control autophagy”.
New directions in research
Selective autophagy
Research is moving from general autophagy towards the precise recognition of specific cellular cargo.
Mitophagy
Scientists are investigating how mitochondrial quality affects metabolism, reactive oxygen species (ROS) and tumour responses to stress.
Tumour immunity
Autophagy can influence immune cells and communication within the tumour microenvironment.
Drug resistance
Some cancer cells may use autophagy as an adaptive mechanism during treatment.
Research aims to establish which tumours, stages and patients might benefit from inhibiting autophagy, promoting it or not targeting it at all.
Findings from cell cultures or animals must be tested in clinical trials. Changes in a biomarker or tumour shrinkage do not automatically mean longer survival. [6, 7]
Common myths
No such universal time point can be reliably established in humans.
GKI does not directly measure autophagic flux.
This is too simplistic. In an established tumour, autophagy can support cell survival under certain circumstances.
This claim does not establish a clinical treatment and can be dangerous, particularly when malnutrition is a risk.
Frequently asked questions
Is autophagy “cellular cleaning”?
That is a simplified analogy. More precisely, it is a regulated lysosomal system for degradation and recycling.
What is an autophagosome?
A double-membrane structure that captures cellular cargo for degradation and subsequently fuses with the lysosomal system.
What is mitophagy?
Selective autophagy that targets mitochondria.
Is autophagy good or bad in cancer?
There is no one-word answer. Its role depends on the biological and clinical context.
Can autophagy be measured at home?
Not reliably with ordinary glucose or ketone measurements. Research on autophagic flux uses specialised methods and biomarkers.
Key points to remember
Autophagy is cellular recycling, not a synonym for cell death. It helps maintain protein and organelle quality and enables metabolic adaptation.
In cancer, autophagy has a paradoxical role that depends on the context. Mechanisms that may support cellular stability before a tumour develops can, under certain circumstances, help cells in an established tumour cope with stress.
Scientific sources
- Nobel Prize in Physiology or Medicine (2016): mechanisms of autophagy. View source
- Qu et al. (2003): Promotion of tumorigenesis by heterozygous disruption of the beclin 1 autophagy gene. Experimental study in mice. View source
- Guo et al. (2011): Activated Ras requires autophagy to maintain oxidative metabolism and tumorigenesis. Preclinical research. View source
- Bensalem et al. (2025): Intermittent time-restricted eating may increase autophagic flux in humans: an exploratory analysis. View source
- Muscaritoli et al. (2021): ESPEN practical guideline: Clinical Nutrition in cancer. View source
- Karasic et al. (2019): randomised trial of chemotherapy with or without hydroxychloroquine in advanced pancreatic cancer. View source
- Zeh et al. (2020): randomised preoperative trial of autophagy inhibition in pancreatic cancer. View source