Researchers tested whether a ketogenic diet (a high-fat, low-carb eating plan) could help people with head and neck cancer or rectal cancer survive longer when combined with radiation and chemotherapy. They followed 81 patients—35 eating a keto diet and 46 eating normally—for several years. While the keto diet appeared safe and may have slightly reduced skin damage from radiation, it didn’t significantly improve survival rates or cancer-free survival compared to a regular diet. The study suggests that keto diets are safe during cancer treatment, but more research is needed to understand if they truly help fight cancer.

The Quick Take

  • What they studied: Whether eating a ketogenic diet (very low carbs, high fat) during radiation and chemotherapy for head and neck or rectal cancer helps patients live longer and stay cancer-free
  • Who participated: 81 cancer patients receiving radiation treatment—35 followed a ketogenic diet and 46 ate a standard diet. Researchers tracked them for an average of 6 years
  • Key finding: The ketogenic diet group did not live significantly longer or stay cancer-free longer than the standard diet group. However, patients on keto had slightly less severe skin damage from radiation
  • What it means for you: If you have head and neck or rectal cancer, a ketogenic diet appears safe to try during treatment, but current evidence doesn’t show it improves survival. Talk to your cancer care team before making major diet changes during treatment

The Research Details

This was a follow-up analysis of the KETOCOMP trial, where researchers compared two groups of cancer patients receiving radiation therapy. One group (35 patients) followed a ketogenic diet during treatment, while the other group (46 patients) ate a regular diet. The researchers tracked both groups for several years, measuring how long patients survived overall, how long they stayed cancer-free, and what side effects they experienced from radiation.

The study used a statistical method called propensity score matching to make the two groups more similar and comparable. This helps reduce bias when comparing groups that weren’t randomly assigned. Researchers measured survival using standard cancer research methods and compared side effects between groups using statistical tests.

The median follow-up time was about 6 years for head and neck cancer patients and about 6 years for rectal cancer patients, which is a substantial amount of time to track outcomes.

This research approach is important because it looks at real-world outcomes over a long period. Rather than just measuring short-term changes in the body, the researchers tracked whether patients actually lived longer and stayed cancer-free—the outcomes that matter most to patients. By following patients for 6+ years, the study captures long-term effects that shorter studies might miss.

Strengths: The study had a long follow-up period (6+ years), which is excellent for cancer research. Researchers used proper statistical methods to compare groups. The study was prospective, meaning they planned it in advance rather than looking back at old records. Limitations: The sample size was relatively small (81 patients total), which makes it harder to detect differences. The groups weren’t randomly assigned to diet types, which could introduce bias. The study was a post-hoc analysis, meaning it analyzed data collected for a different purpose. These factors mean the results should be interpreted cautiously.

What the Results Show

The main finding was that patients on a ketogenic diet did not live significantly longer than those eating a standard diet. For head and neck cancer, the median follow-up was about 6.5 years. The keto group showed a trend toward longer cancer-free survival (100.5 months versus 87.3 months), but this difference was not statistically significant, meaning it could have occurred by chance.

When researchers used advanced statistical matching to make the groups more similar, head and neck cancer patients on keto showed numerically longer overall survival and cancer-free survival, but again these differences were not statistically significant. For rectal cancer patients, there were no meaningful differences between groups in any survival measure.

The most notable finding was that head and neck cancer patients on a ketogenic diet experienced less severe skin damage from radiation therapy. This difference was borderline in one analysis but became statistically significant when all patients were included in the analysis.

Other side effects from radiation therapy—such as mouth sores, difficulty swallowing, and other acute toxicities—were similar between the keto and standard diet groups. This suggests that the ketogenic diet didn’t cause additional harm during treatment. The safety profile was generally favorable for the keto diet group, with no unexpected serious problems reported.

This study adds to a growing body of research exploring whether ketogenic diets might help cancer treatment. The theory is that cancer cells prefer to use sugar (glucose) for energy, so a diet that reduces sugar might slow cancer growth. However, this KETOCOMP trial is one of the first to look at actual survival outcomes in humans. Previous studies were mostly laboratory or animal studies. This research suggests that while the keto diet is safe during cancer treatment, the survival benefits that laboratory studies suggested may not translate to real patients.

The study had several important limitations. First, only 81 patients were studied, which is relatively small for detecting survival differences. Second, patients weren’t randomly assigned to diet groups—they chose their diet—which could introduce bias. Third, this was a post-hoc analysis, meaning researchers analyzed data collected for a different original purpose. Fourth, the study only included patients with head and neck or rectal cancer, so results may not apply to other cancer types. Finally, the study couldn’t determine why some patients chose keto and others didn’t, which might affect results.

The Bottom Line

Based on this research, a ketogenic diet during cancer radiation treatment appears safe (moderate confidence). However, there is currently no strong evidence that it improves survival or cancer-free survival (low confidence). If you’re interested in trying a ketogenic diet during cancer treatment, discuss it with your oncology team first. They can help you implement it safely while ensuring you get adequate nutrition during treatment. Don’t delay or replace standard cancer treatment with diet changes.

This research is relevant to people with head and neck cancer or rectal cancer who are considering dietary changes during radiation therapy. It’s also important for oncologists and nutritionists who advise cancer patients. People with other cancer types should not assume these results apply to them. This research is less relevant to people not undergoing cancer treatment.

Cancer survival benefits, if they exist, typically take months to years to become apparent. This study followed patients for 6+ years, which is the appropriate timeframe for evaluating cancer treatment effectiveness. If you were to try a ketogenic diet during cancer treatment, you wouldn’t expect to see survival benefits immediately—they would only become clear over years of follow-up.

Want to Apply This Research?

  • If using a health app during cancer treatment, track daily macronutrient intake (carbohydrates, fats, proteins) if following a ketogenic diet, along with treatment side effects like skin irritation, appetite changes, and energy levels. Record these weekly to identify patterns.
  • Work with your cancer care team to implement a ketogenic diet safely during treatment. Use the app to log meals, track ketone levels if monitoring them, and record any side effects. Set reminders for medical appointments and medication timing to ensure diet changes don’t interfere with treatment.
  • Maintain long-term tracking of treatment side effects, weight, and overall wellness metrics. Share monthly summaries with your oncology team. Monitor for nutritional deficiencies that might occur on a restrictive diet during intensive cancer treatment. Track energy levels and quality of life indicators alongside physical measurements.

This research summary is for educational purposes only and should not replace professional medical advice. Cancer treatment decisions should always be made in consultation with your oncology team. While this study suggests ketogenic diets are safe during cancer treatment, it does not show they improve survival. Do not delay, avoid, or replace standard cancer treatment (surgery, radiation, chemotherapy) with dietary changes alone. Always inform your cancer care team about any dietary changes you’re considering, as some diets may interact with medications or affect treatment effectiveness. This study involved specific cancer types; results may not apply to other cancers. Individual responses to diet during cancer treatment vary significantly.