Cancer patients, especially those undergoing chemotherapy or radiation, need to be cautious about certain foods that can raise infection risk, interfere with treatment, or worsen side effects. The biggest concerns fall into three categories: foods that carry harmful bacteria, foods and drinks that interact with cancer drugs, and foods that promote inflammation in an already stressed body.
Raw and Undercooked Foods
Cancer treatment often weakens your immune system, making you far more vulnerable to foodborne infections that a healthy body would normally fight off. The foods most likely to cause trouble are ones that haven’t been fully cooked or pasteurized.
Raw and undercooked meats top the list. That means no rare or medium-rare steaks, no pink burgers, and no raw seafood like sushi or oysters. Poultry should reach an internal temperature of 165°F, ground meats 160°F, and steaks, fish, and shellfish 145°F. A food thermometer is worth the small investment. Deli meats, hot dogs, and smoked fish (labeled “lox,” “kippered,” or “nova style”) also need to be heated until steaming hot before you eat them, since they can harbor bacteria even when refrigerated.
Raw or undercooked eggs are another concern. That includes homemade mayonnaise, fresh Caesar dressing, aioli, raw cookie dough, and homemade eggnog. Soft-cooked eggs with runny yolks fall into this category too.
For dairy, avoid unpasteurized milk and any cheese made from it. Soft cheeses like Brie, Camembert, queso fresco, and goat cheese are often made with unpasteurized milk unless the label states otherwise. Mold-ripened cheeses like blue cheese, Gorgonzola, Roquefort, and Stilton should also be skipped. Soft-serve ice cream and frozen yogurt from machines can harbor bacteria, and cheese sliced at the deli counter carries more risk than pre-packaged options. Fermented dairy products like kefir are best avoided during active treatment as well.
Uncooked tofu, tempeh, and miso products also pose a risk. If you eat these foods, cook them thoroughly first. And always wash fruits and vegetables before eating them, even if you plan to peel them.
Alcohol During Treatment
Alcohol creates several problems during cancer treatment. Many chemotherapy drugs are broken down by the liver, and alcohol is processed there too. Drinking during treatment triggers liver inflammation that can impair how your body metabolizes these drugs, potentially increasing side effects.
If you have mouth sores from chemotherapy or head and neck radiation, alcohol will irritate them and may make them worse. Beyond the treatment interactions, ethanol itself is a known carcinogen. Its breakdown product, acetaldehyde, disrupts DNA repair and contributes to tissue damage, inflammation, and interference with estrogen pathways. The type of alcohol doesn’t matter: beer, wine, and spirits all contain ethanol and carry the same risks.
Grapefruit and Drug Interactions
Grapefruit and Seville (sour) oranges can dangerously alter how your body handles certain medications, including some cancer drugs. Grapefruit juice blocks an enzyme in your small intestine that normally breaks down drugs before they enter your bloodstream. When that enzyme is blocked, more of the drug floods into your system and stays there longer, which can amplify side effects. In some cases, grapefruit affects transport proteins that move drugs into cells, making the medication less effective instead.
If you’re on any cancer medications, ask your oncologist or pharmacist whether grapefruit is safe. This applies to the whole fruit, the juice, and products flavored with it.
Herbal Supplements
Several popular herbal supplements can interfere with chemotherapy. St. John’s wort, commonly taken for depression, is one of the most well-documented offenders. It affects the same liver enzymes that process many cancer drugs, potentially making treatment less effective or more toxic. Concentrated green tea extracts can cause similar issues. These aren’t theoretical risks: the National Cancer Institute specifically flags them as concerns for patients on active treatment.
The safest approach is to tell your cancer care team about every supplement, vitamin, and herbal product you take, even ones that seem harmless.
Ultra-Processed and Fried Foods
Highly processed foods deserve extra attention during cancer treatment. A large study tracking over 200,000 people in the UK Biobank found that every 10 percentage point increase in ultra-processed food consumption was linked to a 6% higher risk of dying from cancer overall, with sharper increases for ovarian cancer (30% higher mortality) and breast cancer (16% higher mortality). These foods tend to be high in salt, sugar, and unhealthy fats while low in fiber, and they contain additives, artificial sweeteners, and packaging-related contaminants that may contribute to poor outcomes.
Fried foods cooked in hydrogenated oils can increase inflammation, which is the last thing your body needs while fighting cancer and coping with treatment. Processed meats like bacon, sausage, and cured salamis contain nitrate and nitrite additives that have been linked to increased risk of breast and prostate cancer.
The Truth About Sugar
You’ve probably heard that “sugar feeds cancer.” The reality is more nuanced. A 2025 lab study from the National Cancer Institute found that fructose did fuel tumor growth in animals, but not directly. The liver converted fructose into specific fats, which cancer cells then used as fuel. However, the researchers were clear that this is not a reason to try eliminating all sugar from your diet.
The sugars in whole fruits and vegetables are metabolized differently by the body than the high-fructose corn syrup in processed foods. As one NCI researcher put it: “Apples are still healthy; junk food still isn’t.” The practical takeaway is to limit added sugars from sodas, candy, and packaged snacks while continuing to eat whole fruits and vegetables freely.
What About Restrictive Diets?
Cancer patients sometimes consider extreme dietary changes like ketogenic diets, prolonged fasting, or cutting out entire food groups. The American Society of Clinical Oncology reviewed the evidence and found that there is currently insufficient data to recommend any of these approaches for improving quality of life, reducing treatment toxicity, or controlling cancer. Interestingly, ASCO also found that strictly banning raw fruits and vegetables (the traditional “neutropenic diet”) does not appear to prevent infections, and the potential harms of nutritional restriction likely outweigh any benefit.
Maintaining adequate nutrition during treatment matters more than following a rigid set of food rules. Your body needs calories, protein, and nutrients to tolerate treatment, heal tissue, and support your immune system. Any dietary changes should be guided by your treatment team, who can tailor recommendations to your specific cancer type, treatment regimen, and overall health.