Researchers in Italy are testing whether eating a Mediterranean diet—full of vegetables, whole grains, and healthy oils—can help people with advanced colorectal cancer feel better during chemotherapy treatment. The study focuses on the trillions of tiny bacteria living in our stomachs, called the gut microbiota, which may affect how our bodies handle cancer drugs. Forty patients will eat either a Mediterranean diet or a typical Western diet while receiving chemotherapy, and scientists will track their stomach bacteria and side effects. This research could show that what we eat plays an important role in managing cancer treatment and reducing uncomfortable symptoms like nausea and digestive problems.

The Quick Take

  • What they studied: Whether eating a Mediterranean diet (lots of vegetables, whole grains, fish, and olive oil) instead of a typical Western diet (lots of meat, sugar, and processed foods) helps cancer patients experience fewer side effects from chemotherapy and changes their gut bacteria in helpful ways.
  • Who participated: Forty patients in Italy with advanced colorectal cancer who are starting their first round of chemotherapy treatment. Half will eat a Mediterranean diet, and half will eat their normal diet.
  • Key finding: This is a pilot study still in progress (17 patients enrolled as of the publication date), so final results won’t be available until October 2028. The researchers are measuring changes in gut bacteria and tracking how many patients experience stomach-related side effects from chemotherapy.
  • What it means for you: If the study shows positive results, it may suggest that cancer patients could reduce chemotherapy side effects by changing their diet—something simple they can control themselves. However, this is early-stage research, and people should not change their diet during cancer treatment without talking to their doctor first.

The Research Details

This is a pilot study, which means it’s a small test run before doing a larger study. Forty patients with advanced colorectal cancer were randomly divided into two groups: one group eats a modified Mediterranean diet (rich in vegetables, whole grains, fish, and olive oil, low in red meat and processed foods), while the other group eats whatever they normally eat. Both groups receive the same chemotherapy treatment. Scientists collect blood and stool samples at the beginning, after three chemotherapy cycles, and after six cycles to analyze the bacteria in patients’ guts and measure chemical changes in their bodies. The study is being conducted at a single hospital in Italy and is open-label, meaning both patients and doctors know which diet group each person is in.

The gut bacteria in our stomachs play a bigger role in our health than scientists used to think. Research suggests that people eating Western diets (lots of processed foods and meat) have different gut bacteria than people eating Mediterranean diets, and these differences might affect how well cancer drugs work and how many side effects patients experience. By studying this connection in cancer patients, researchers hope to find a simple, non-drug way to help people tolerate chemotherapy better.

This is a well-designed pilot study with ethics approval, but it’s important to understand its limitations: it’s small (only 40 patients), it’s still ongoing (results won’t be ready until 2028), and it’s not yet published in a peer-reviewed journal. The study is randomized and controlled, which are good features that help ensure fair comparisons. However, because patients and doctors know which diet group each person is in, there’s a possibility that knowing about the diet could influence how patients report their symptoms.

What the Results Show

As of the publication date, the study is still recruiting and collecting data—only 17 of the 40 planned patients have been enrolled. The main goal is to measure the ratio of two types of bacteria (Firmicutes and Bacteroidetes) in patients’ guts after three rounds of chemotherapy. This ratio is important because an imbalance in these bacteria has been linked to worse side effects from cancer treatment. The researchers will compare how this ratio changes in patients eating the Mediterranean diet versus those eating a Western diet. Early data collection is ongoing, and the study won’t be complete until mid-2025 at the earliest.

The researchers are also tracking: (1) how many patients experience stomach and digestive side effects from chemotherapy, (2) how many patients experience severe (grade 3 or 4) digestive side effects, and (3) changes in the overall mix of bacteria in the gut and chemical markers in the blood and stool. These measurements will be taken after three chemotherapy cycles and again after six cycles. The study will also examine whether the Mediterranean diet helps patients tolerate their cancer drugs better, which could mean they can continue treatment without interruptions.

Previous research has shown that people eating Mediterranean diets have healthier gut bacteria and lower rates of colorectal cancer compared to people eating Western diets. One study in melanoma (skin cancer) patients found that eating high-fiber diets reduced chemotherapy side effects. This new study builds on those findings by specifically testing whether diet changes can help people with advanced colorectal cancer handle chemotherapy better. If successful, it would be one of the first studies to directly prove this connection in cancer patients.

This is a pilot study, so it’s small and designed to test whether the idea is worth studying on a larger scale. The study is not yet complete, so we don’t have final results. Because patients and doctors know which diet group each person is in, there’s a possibility of bias—for example, patients expecting the Mediterranean diet to help might report fewer symptoms. The study is only being done in Italy with Italian patients, so results might not apply to people in other countries with different food cultures. Additionally, patients receiving different types of chemotherapy drugs or biological agents might respond differently to the diet changes.

The Bottom Line

This research is too early to make specific recommendations. Wait for the final results (expected in 2028) before making major diet changes during cancer treatment. If you’re a colorectal cancer patient undergoing chemotherapy, talk to your doctor or a registered dietitian before changing your diet. A Mediterranean diet is generally considered healthy for the general population, but during cancer treatment, your nutritional needs are special and require professional guidance. Confidence level: Low (pilot study, results not yet available).

This research is most relevant to: (1) people with advanced colorectal cancer starting chemotherapy, (2) their doctors and nutritionists, (3) cancer researchers studying how diet affects treatment, and (4) public health officials interested in improving cancer care. People with other types of cancer should not assume these results apply to them without more research. People not undergoing cancer treatment should not use this as a reason to change their diet, though a Mediterranean diet is generally recommended for overall health.

If the Mediterranean diet does help reduce chemotherapy side effects, patients would likely notice improvements within the first few weeks to months of treatment. However, changes in gut bacteria take time—usually several weeks to months—so benefits might not be immediate. The full study won’t be complete until 2028, so patients shouldn’t expect recommendations based on this research for at least 3-4 years.

Want to Apply This Research?

  • If you’re a cancer patient, track daily: (1) which foods you eat (especially noting Mediterranean diet foods like vegetables, whole grains, fish, and olive oil), (2) digestive symptoms (nausea, diarrhea, constipation, appetite) on a scale of 1-10, and (3) energy levels. This creates a personal record to share with your medical team.
  • Work with your doctor or dietitian to gradually add more Mediterranean diet foods: increase vegetables and whole grains, switch to olive oil for cooking, eat fish twice a week, and reduce red meat and processed foods. Track how you feel with each change to identify which foods help you tolerate chemotherapy better.
  • Keep a weekly food and symptom diary during chemotherapy cycles. Note which meals or foods seem to reduce nausea or digestive problems. Share this information with your medical team at each appointment. After treatment ends, continue tracking to see if dietary patterns affect your recovery and long-term health.

This is a pilot study that is still in progress and has not yet published final results. Do not make changes to your diet or cancer treatment based on this research without consulting your oncologist and a registered dietitian. This study is designed to test whether a larger study is feasible and worthwhile—it is not yet proven that a Mediterranean diet reduces chemotherapy side effects in cancer patients. If you are undergoing cancer treatment, all dietary changes must be discussed with your medical team, as some foods may interact with medications or affect treatment effectiveness. This summary is for educational purposes only and should not replace professional medical advice.