What Not To Eat During Immunotherapy?

Immunotherapy helps your immune system fight cancer, but what you eat during treatment matters more than many people realize. Some foods and drinks can interfere with how these drugs work, while others can put you at higher risk for serious infections. The short answer is that you should avoid unpasteurized dairy, raw or undercooked meats and eggs, certain herbal supplements, and grapefruit and related citrus fruits during most immunotherapy treatments. The longer answer depends on the specific drug you are receiving, so always confirm your personal food restrictions with your oncology team.

Why Your Diet Matters During Immunotherapy

Immunotherapy drugs work by taking the brakes off your immune system so it can attack cancer cells. That is their purpose. But a fully activated immune system can also attack healthy tissue, which is why side effects like colitis, hepatitis, and skin rashes happen.

Food does not directly stop the drug from working in most cases. The bigger risks are infection and drug interactions. Many immunotherapy patients have weakened immune systems from the cancer itself or from other treatments like chemotherapy. That makes foodborne illness a real danger, not just an inconvenience.

The other concern is that some foods and supplements change how your liver processes medications. That can alter drug levels in your blood, making treatment less effective or more toxic.

What Not To Eat During Immunotherapy: High-Risk Foods

The most important rule is food safety. Immunotherapy can make you more vulnerable to infections, and foodborne bacteria that a healthy person shakes off can become serious for you.

Avoid these foods during treatment:

• Raw or undercooked meat, poultry, and fish — including sushi, rare steak, and raw oysters
• Raw or undercooked eggs — including homemade mayonnaise, hollandaise sauce, and runny yolks
• Unpasteurized milk and soft cheeses — including raw milk, feta, brie, camembert, and blue-veined cheeses
• Raw sprouts — including alfalfa, clover, and radish sprouts
• Unwashed fruits and vegetables — especially those eaten with the skin on
• Leftovers older than three days — bacteria multiply quickly even in the refrigerator

These foods carry bacteria like Listeria, Salmonella, and E. coli. For someone with a suppressed immune system, these infections can become life-threatening.

Cook all meat to a safe internal temperature. Wash all produce thoroughly under running water. When in doubt, throw it out.

Grapefruit and Certain Citrus Fruits

Grapefruit is the most well-known food that interferes with medication processing. It blocks an enzyme in your liver called CYP3A4, which is responsible for breaking down many drugs.

When that enzyme is blocked, medication levels can rise in your blood. Higher levels mean more side effects, and in some cases, levels high enough to be dangerous.

Seville oranges, pomelos, and tangelos have the same effect. Regular oranges and lemons are generally safe, but check with your care team before assuming anything.

Not all immunotherapy drugs are affected by grapefruit. But some are, and your oncology pharmacist will know which ones. If they tell you to avoid grapefruit, take that seriously. It is not a suggestion.

Herbal Supplements and Immunotherapy

Herbal supplements are not regulated like prescription drugs, and many of them interact with cancer treatments in ways that are not fully understood.

Some supplements can stimulate the immune system in ways that worsen immunotherapy side effects. Others can interfere with how your body processes the drug. The evidence for most individual herbs is limited, but the risk is real.

Supplements to avoid or discuss with your doctor include:

• St. John’s Wort — known to speed up liver enzymes and reduce drug effectiveness
• Echinacea — stimulates immune activity, which may worsen autoimmune side effects
• Green tea extract — concentrated forms may cause liver damage, which is especially risky during immunotherapy
• High-dose vitamin C — no proven benefit during immunotherapy and possible interference
• Maitake and other medicinal mushrooms — some may affect immune function, but evidence is unclear

No clinical guidelines currently exist for most herbal supplements during immunotherapy. The safest position is to stop all supplements unless your oncology team explicitly approves them. Tell your doctor about every supplement you take, including vitamins and minerals.

Alcohol During Immunotherapy

Alcohol is not strictly forbidden during most immunotherapy treatments, but it deserves caution.

Alcohol can dehydrate you, which matters because many immunotherapy patients already struggle with fatigue and digestive issues. It also puts extra work on your liver, and some immunotherapy drugs already carry a risk of liver inflammation.

If you drink alcohol, the safest approach is to keep it minimal or skip it entirely during active treatment. Ask your oncology team about your specific situation. Some drugs have stronger interactions with alcohol than others.

Foods That May Help During Immunotherapy

The evidence for specific “anti-cancer” foods during immunotherapy is weak. No food has been proven to make immunotherapy work better.

What is well established is that good nutrition supports your body’s ability to tolerate treatment. Adequate protein helps maintain muscle mass. Enough calories prevent unintended weight loss. A varied diet provides the vitamins and minerals your body needs to recover between cycles.

Focus on:

• Cooked vegetables — easier to digest and safer than raw
• Lean proteins — chicken, fish, eggs cooked fully, tofu
• Whole grains — rice, oats, quinoa, whole wheat bread
• Pasteurized dairy — yogurt, milk, hard cheeses
• Fruits you can wash or peel — bananas, oranges, melons, cooked apples

If you are losing weight or struggling to eat, talk to a registered dietitian who works with cancer patients. They can help you find foods you can tolerate and keep your nutrition on track.

Common Myths About Diet and Immunotherapy

You will see a lot of claims online about foods that “boost” immunotherapy or diets that “starve” cancer. Most of these claims are not supported by clinical evidence.

One common myth is that sugar feeds cancer and should be completely eliminated. Sugar does feed cancer cells, but it also feeds every other cell in your body. There is no evidence that cutting all sugar improves immunotherapy outcomes. What matters more is maintaining a healthy weight and getting enough nutrition.

Another myth is that fasting during treatment makes immunotherapy more effective. Some research in animals suggests this might be true, but no large human trials have confirmed it. Fasting while your body is fighting cancer and dealing with treatment side effects can be dangerous.

Some sources claim that a ketogenic diet enhances immunotherapy. The evidence is mixed and mostly preliminary. No current clinical guidelines recommend a ketogenic diet during immunotherapy.

The honest position is this: no specific diet has been proven to improve immunotherapy results. What has been proven is that malnutrition and unsafe food handling cause real harm during treatment.

Questions To Ask Your Oncology Team

Your medical team is the only reliable source for your specific food restrictions. Before you start treatment, ask these questions:

• Are there any foods or drinks I should avoid with my specific drug?
• Do I need to worry about grapefruit or other citrus?
• Which supplements should I stop taking?
• Is it safe for me to eat raw fruits and vegetables?
• Should I limit alcohol during treatment?

Write down the answers and keep them somewhere visible. It is easy to forget details when you are managing appointments, side effects, and the stress of treatment.

If you are unsure whether a food is safe, do not eat it until you ask. A quick phone call to your oncology nurse can save you from a serious infection or a drug interaction.