Short-Term Fasting in Cancer: Treating the Metabolic Environment the Tumor Lives In, Rather Than the Tumor Itself

Short-Term Fasting During Chemotherapy: Can a Metabolic Intervention Improve Treatment Response in Ovarian Cancer?

Metabolism Is Becoming a New Frontier in Cancer Treatment

High-grade serous ovarian cancer is often diagnosed at an advanced stage. Primary surgery may not initially be possible in many patients; in that setting, neoadjuvant carboplatin and paclitaxel are administered, followed by assessment for interval cytoreductive surgery. This clinical model provides a distinctive research setting in which chemotherapy response can be measured quickly and pathological response can be assessed during surgery.

The underlying idea is that insulin, IGF-1, and nutrient-sensitive growth signals may support survival pathways in some tumor cells. Short-term fasting may suppress these signals, shift healthy cells into a more protected metabolic state, and make cancer cells more sensitive to chemotherapy. In the literature, this concept is sometimes discussed as differential stress resistance and differential stress sensitization : normal cells may adapt to fasting stress, whereas rapidly dividing cancer cells may be unable to show the same adaptive flexibility.

This pilot study at ASCO 2026 suggests that the biological hypothesis may have a measurable clinical counterpart. However, one point must be emphasized from the outset: these data are exciting, but they are not yet sufficient to change standard treatment. The study is small, single-center, and exploratory; higher-risk patient groups, including those with diabetes, malnutrition, or eating disorders, were excluded.

A Pilot Randomized Study in 36 Patients

This was a prospective, two-arm pilot randomized study conducted at a single center in Rome. It enrolled patients with newly diagnosed, advanced high-grade serous ovarian cancer who were considered unsuitable for primary cytoreductive surgery and required neoadjuvant chemotherapy.

Patients had to have a body mass index of at least 19 kg/m². Conditions such as diabetes, food allergy, eating disorders, and malnutrition were exclusion criteria. This detail is clinically crucial: the study does not say that “every cancer patient should fast around chemotherapy.” Instead, it describes a controlled research protocol used in selected, closely monitored patients.

The Short-Term Fasting Protocol: Controlled Low Calorie Intake, Not Complete Fasting

In the short-term fasting arm, patients followed a fasting protocol around each chemotherapy cycle, starting 36 hours before chemotherapy and continuing until 24 hours after chemotherapy ended. Daily calorie intake was no more than 350 kcal . Water and herbal tea were allowed freely; up to 2 liters of vegetable juice daily and small amounts of light vegetable broth/soup were also permitted. Between chemotherapy sessions, patients returned to their normal diet.

A ketogenic diet arm was initially planned as well, but it was closed early because adherence was poor. This detail shows that, in nutritional interventions, alongside biology, the issues of feasibility and patient adherence are also decisive.

Insulin Response: The Metabolic Target Really Changed

The primary endpoint was the change in mean insulin level after three cycles of neoadjuvant chemotherapy. The finding was clear: in the unrestricted diet arm, insulin increased by a mean of +9,76 µIU/mL whereas, in the short-term fasting arm, it decreased by -1,12 µIU/mL .

Pathological Response: Complete or Near-Complete Response Increased More Than 3-Fold

In the chemotherapy response score assessed during interval cytoreductive surgery, the rate of CRS 3, meaning a complete or near-complete response, was %58,8 in the short-term fasting arm, compared with %17,6 in the unrestricted diet arm.

In absolute terms, the difference was 41,2 percentage points . Put more simply, the rate of complete or near-complete pathological response in the short-term fasting arm appeared to be approximately 3,3 times the rate in the unrestricted diet arm. Rates can fluctuate in small studies, but a pathological response difference of this magnitude provides a strong rationale for larger randomized studies.

Progression-Free Survival: 38 Months Versus 24 Months

After a median follow-up of approximately 18 months, median progression-free survival was reported as 38 monthsin the short-term fasting arm, compared with 24 months in the unrestricted diet arm. This represents an absolute difference of 14 months .

Fasting, GLP-1, and Metabolic Oncology Point in the Same Direction

This study does not directly use a GLP-1 agonist. Semaglutide, tirzepatide, or a similar drug is not part of the study. Nevertheless, the biological message is similar: cancer treatment may need to target not only the tumor but also the metabolic environment that nourishes it.

GLP-1 receptor agonists also became a noteworthy topic at ASCO 2026. Particularly in real-world data, signals were reported suggesting a potentially lower risk of metastatic progression in some cancer patients using GLP-1 agonists. For example, a propensity-matched analysis of 12.112 patients found an apparently lower rate of progression to stage IV in patients using GLP-1 agonists with some early-stage obesity-related cancers. The difference was reported as statistically significant in lung, breast, colorectal, and liver cancers.

What Does “Perichemotherapy Fasting” Mean?

“Perichemotherapy fasting” means controlled restriction of food intake within a brief window immediately before and after a chemotherapy cycle. Its purpose is not long-term weight loss or chronic calorie restriction. The aim is to temporarily alter the metabolic environment surrounding the tumor cell during chemotherapy.

This approach may become more relevant in diseases in which insulin and nutrient-sensitive growth signals may contribute to tumor biology. The exclusion of patients with diabetes from the ovarian cancer study is noteworthy. A central future question will be how this approach can be used safely and effectively precisely in patients with diabetes, prediabetes, obesity, and insulin resistance.

Not Yet Standard, but No Longer Something to Ignore

The direct message for everyday practice is not that “everyone receiving chemotherapy should fast.” The correct message is more nuanced: the patient’s metabolic profile should be part of the treatment plan. At diagnosis, systematic assessment should include not only tumor markers, staging imaging, and molecular tests, but also body composition, glucose metabolism, insulin resistance, diabetes control, and nutritional risk.

A New Threshold in Cancer Treatment: Treating Not Only the Tumor, but Also the Metabolic Environment It Lives In

This pilot randomized study to be presented at ASCO 2026 provides a noteworthy signal that short-term fasting around chemotherapy in high-grade serous ovarian cancer may affect not only metabolic parameters but also oncological outcomes, such as pathological response and progression-free survival.

After three cycles of neoadjuvant chemotherapy, insulin increased in the unrestricted diet arm but decreased in the short-term fasting arm. The CRS 3 pathological response rate rose from 17,6% to 58,8%. At approximately 18 months of follow-up, median PFS extended from 24 to 38 months. These figures are exceptionally noteworthy for a small pilot study. For that very reason, however, they cannot become a clinical standard without confirmation in large, multicenter, well-controlled studies.

Nevertheless, the direction is clear: oncology will not consist solely of genomics, immunotherapy, and precision drugs. In the coming period, insulin resistance, obesity, diabetes, nutritional rhythms, GLP-1 agonists, exercise, and metabolic inflammation will become more visible components of cancer treatment. “Perichemotherapy fasting” may look like a new trend today, but with the right patient, protocol, and monitoring, it could become an important tool in metabolic oncology in the future.