Chemotherapy can take a toll on the body, weakening the immune system and affecting digestion. While eating nutritious foods can help support recovery, certain foods should be avoided to prevent complications and ensure a smoother treatment experience.

If you or a loved one are undergoing chemotherapy, here are 10 foods and beverages to steer clear of—and why they could be harmful during treatment.

1. Grapefruit & Grapefruit Juice 🍊

Grapefruit contains enzymes that interfere with drug metabolism, which can affect the effectiveness of chemotherapy medications. Since this interaction can alter how your body processes treatment, it’s best to avoid grapefruit and grapefruit juice.

💡 Tip: Ask your oncologist or pharmacist if any of your medications interact with grapefruit.

2. Raw Meat & Raw Fish 🍣

Raw meats, including sushi, carpaccio, and tartare, may contain harmful bacteria and parasites. Because chemotherapy weakens the immune system, your body may not be able to fight off infections from undercooked or raw foods as effectively.

💡 Tip: Stick to fully cooked meats and fish to reduce infection risk.

3. Unwashed Fruits & Vegetables 🥗

While fruits and vegetables are essential for a balanced diet, consuming them unwashed can introduce bacteria, viruses, and parasites into the body. During chemotherapy, when the immune system is compromised, these contaminants can cause serious infections.

💡 Tip: Always wash fresh produce thoroughly, even if it's organic.

4. Alcohol 🍷

Alcohol can stress the liver, which is already working hard to process chemotherapy drugs. Additionally, excessive alcohol intake may lead to abnormal liver function tests, which could delay or disrupt treatment.

💡 Tip: If you drink, consult your doctor to determine if moderate consumption is safe for you.

5. Caffeinated Beverages ☕

Chemotherapy can cause sleep disturbances, and consuming caffeine late in the day can worsen insomnia. Additionally, caffeine may contribute to dehydration, which is already a concern for many chemotherapy patients.

💡 Tip: If you need a pick-me-up, opt for decaf herbal teas or water with lemon instead of coffee or energy drinks.

6. Unpasteurized Dairy 🥛

Soft cheeses and unpasteurized dairy products, such as brie, camembert, and some types of goat cheese, can harbor bacteria like Listeria, which poses a serious risk to chemotherapy patients.

💡 Tip: Choose pasteurized dairy products to enjoy cheese and milk safely.

7. Certain Supplements & Herbs 🌿

Some supplements can interfere with chemotherapy's effectiveness. In particular:

Antioxidant supplements (like high doses of vitamin C or E) may reduce the effectiveness of chemotherapy.
Garlic acts as a natural blood thinner, which can increase the risk of bleeding if your platelet levels are low.
St. John’s Wort may interfere with drug metabolism, making chemotherapy less effective.

💡 Tip: Get nutrients from food rather than supplements unless prescribed by your doctor.

8. Processed & Sugary Foods 🍩

Highly processed foods often contain preservatives, artificial ingredients, and unhealthy fats. They can contribute to weight gain, inflammation, and even depression—all of which can negatively impact chemotherapy recovery.

Sugary foods can also spike blood sugar levels, potentially increasing fatigue and inflammation.

💡 Tip: Choose whole, nutrient-rich foods over processed options whenever possible.

9. Deli Meats 🥪

Sliced deli meats that sit out for long periods may become contaminated with harmful bacteria, such as Listeria, which can cause severe infections.

💡 Tip: If you want deli meats, opt for pre-packaged, vacuum-sealed options with clear expiration dates.

10. Foods That Cause Digestive Discomfort 🚫

Some foods can worsen chemotherapy side effects, such as nausea, bloating, or diarrhea. These include:

Spicy foods – May irritate the stomach lining.
Greasy or fried foods – Harder to digest.
Carbonated drinks – Can cause bloating and discomfort.

💡 Tip: Eat small, gentle meals that are easy on the stomach, such as bananas, oatmeal, and broth-based soups.

Final Thoughts

Eating the right foods during chemotherapy can boost energy, reduce side effects, and promote healing. By avoiding raw, processed, and potentially harmful foods, you can protect your immune system and improve your overall well-being during treatment.

**About Dr. Jennifer Griggs**

A long-time practicing oncologist and professor at the University of Michigan, Jennifer has received several awards for her medical excellence and published over 150 original research articles as well as numerous editorials and book chapters. She is also a speaker and advocate, committed to improving the quality of medical care and reducing the barriers to equity among the disenfranchised.

For more information on how HuMOLYTE can support your gut health during chemotherapy, visit our product page or consult your health care provider.

This blog was reviewed by Dr. Sourabh Kharait.

This blog is for educational purposes only and is not intended as medical advice. Always consult with your healthcare provider before making any changes to your treatment plan, hydration strategies, or diet. The information provided here is based on general insights and may not apply to individual circumstances.

10 Foods to Avoid During Chemotherapy