Nutrition During Targeted Therapy: Managing Food-Related Side Effects

Targeted therapy blocks specific proteins that help cancer cells grow and spread. Because it works differently from chemotherapy, its side effects differ too, and many of them, such as diarrhoea, mouth sores, nausea, and appetite loss, directly affect eating. 

Good targeted therapy nutrition focuses on maintaining food and fluid intake and strength while managing symptoms and avoiding food-drug problems. Cancer treatment nutrition is never one-size-fits-all, so an oncology dietitian can tailor advice to your drug, symptoms, and preferences. 

In this article, we explain which food-related side effects are common, what a practical diet during targeted therapy looks like, and how food can interact with oral cancer drugs.

Key Takeaways

• Expect food-related side effects: Diarrhoea, mouth sores, nausea, and appetite loss can all reduce intake. 

• Match food to symptoms: A targeted therapy side effects diet uses bland, soft, or small, frequent meals depending on the symptom. 

• Check food-drug interactions: Some tablets are taken fasting, and grapefruit or supplements may matter. 

• Stay hydrated: Replace fluids lost to diarrhoea or poor intake, within your team’s advice. 

• Report problems early: Early advice helps prevent weight loss and dehydration. 

Table of Contents 

What Is Targeted Therapy and Which Side Effects Affect Eating? 

Targeted therapy interferes with specific proteins that control how cancer cells grow, divide, and spread, whereas chemotherapy affects many rapidly dividing cells. Most are small-molecule tablets or capsules, or monoclonal antibodies given by vein. 

The NCI lists diarrhoea and liver problems as the most common side effects, with mouth sores, rash, dry skin, high blood pressure, and fatigue also reported. Medicines can prevent or treat many of them, and most ease after treatment ends. Because these effects change how easily you can eat, targeted therapy nutrition needs to adapt to the drug you take. Medicines can prevent or treat many of them, and most ease after treatment ends. Because these effects change how easily you can eat, targeted therapy nutrition needs to adapt to the drug you take. 

Targeted Therapy Nutrition: Why Eating Well Matters 

Side effects can lower food and fluid intake, making it harder to maintain weight and muscle. One study examined 25 people taking osimertinib, 36% were malnourished and 20% had reduced muscle strength. This is why individualised nutritional care matters during targeted therapy.  

For diarrhoea, a review of EGFR inhibitor toxicities suggests the BRAT diet (bananas, rice, applesauce, toast) until symptoms settle, avoiding gas-forming vegetables like cabbage, broccoli, and Brussels sprouts, drinking about 3-4 litres of fluid to prevent dehydration, and skipping milk products for about a week afterwards. 

Cancer treatment nutrition does not aim for a perfect diet. It aims for enough energy, protein, and fluid to stay strong through treatment, using foods your symptoms allow. 

Targeted Therapy Side Effects Diet: Symptom by Symptom

• Diarrhoea: Common with EGFR-targeted drugs. A review of EGFR inhibitor toxicities advises the BRAT diet (bananas, rice, applesauce, toast) until symptoms settle, avoiding greasy, spicy, fried, and gas-forming foods like cabbage and broccoli, drinking 3-4 litres of fluid, and skipping milk products for about a week. Tell your team early, as medicines may be needed.. 

• Mouth sores: Choose soft, moist, mild foods such as curd rice, khichdi, mashed vegetables, and smoothies, and avoid very spicy or acidic foods. Good oral hygiene also helps: brush gently with a soft toothbrush, rinse with saline, and avoid alcohol-based mouthwashes, which can irritate the mouth. See our guide to foods to eat during chemotherapy. 

• The oral care advice comes from the same Melosky & Hirsh review. It also mentions flossing, which I left out to keep this short. 

• Nausea and appetite loss: Eat small, frequent meals, try cool or room-temperature foods if smells bother you, and add energy-dense foods. See high-calorie meals for cancer patients. 

• Rash and dry skin: These rarely need a special diet. Follow your team’s skin-care advice. 

• Fatigue: See our guide to nutrition for cancer-related fatigue. 

Diet During Targeted Therapy: What to Eat

A diet during targeted therapy should be adapted to your symptoms, appetite, and food preferences. 

Our guide to high-protein foods for cancer patients has more ideas. 

Staying Hydrated With Diarrhoea or Poor Intake

The same review explains that EGFR inhibitor diarrhoea can lead to dehydration and electrolyte problems, so any targeted therapy side effects diet should treat fluids as seriously as food. Sip water, soups, or oral rehydration solution through the day, and tell your team if diarrhoea continues. 

Some guidance suggests limiting milk products briefly after an episode. Ask your team first if dairy is a main protein source for you.

Food-Drug Interactions: Ask Before You Change Your Diet

Food can change how much of an oral cancer drug your body absorbs. A review of food effects notes that erlotinib, lapatinib, nilotinib, pazopanib, and abiraterone are labelled for fasting because food increases their absorption. Take each drug as prescribed. 

Grapefruit can affect levels of some drugs, though evidence varies. A small sunitinib study found only a marginal effect, but labels differ, so check with your pharmacist. Avoid herbal products and high-dose supplements unless your oncology team approves them.

Practical Meal Tips for Low-Energy Days

Simple cancer treatment nutrition habits can help when energy is low: 

• Eat small, frequent meals: Smaller portions are easier when appetite is low. 

• Keep easy foods ready: Curd, bananas, boiled eggs, milkshakes, smoothies, and nutritional supplements need little effort. 

• Plan around your energy: Eat your main meal when you feel best, and ask family to help. 

• Add energy gently: A little ghee, oil, or nut butter adds calories without a bigger portion, if tolerated. 

What Does an Oncology Dietitian Do?

Nutrition for targeted cancer therapy works best with a dietitian who reviews your intake and weight, adapts foods to your side effects, checks that meal timing suits your medicine, and coordinates with your oncologist. Unsure when to start? Read when should you consult an oncology nutritionist.

When to Contact Your Healthcare Team Urgently

Contact your oncology team without delay if you: 

• Have diarrhoea that is severe, persistent, or comes with dizziness or dehydration 

• Cannot keep fluids or medicines down 

• Have fever, severe stomach pain, severe mouth pain, or cannot swallow 

• Are losing weight rapidly or cannot eat for more than a day

Final Thought

Targeted therapy nutrition means matching food to side effects, staying hydrated, and checking food-drug interactions. A diet during targeted therapy does not need to be perfect, only manageable and safe for your drug. If symptoms are reducing your intake, speak early with your cancer care team and an oncology dietitian. 

Need Personalised Cancer Nutrition Support? 

At Oncoheal Nutrition, we offer nutrition for targeted cancer therapy tailored to your drug, side effects, and food preferences. Book a Consultation with our oncology nutrition team. 

Disclaimer: This article is for general educational purposes only and does not replace medical advice, diagnosis, or treatment. Please consult your oncologist and a qualified oncology dietitian before making significant dietary changes or taking supplements.

References 

1. National Cancer Institute. Targeted Therapy for Cancer. Read the page 
2. Muscaritoli M, Arends J, Bachmann P, et al. ESPEN practical guideline: Clinical Nutrition in cancer. Clinical Nutrition. 2021;40(5):2898-2913. Read the guideline on PubMed 
3. Melosky B, Hirsh V. Management of Common Toxicities in Metastatic NSCLC Related to Anti-Lung Cancer Therapies with EGFR-TKIs. Frontiers in Oncology. 2014;4:238. Read the review 
4. Ratain MJ. Importance of Food Effects for Oral Oncology Drugs. Hematology & Oncology. 2012. Read the article 
5. van Erp NP, et al. Marginal increase of sunitinib exposure by grapefruit juice. Cancer Chemotherapy and Pharmacology. 2011;67(3):695-703. Read the study 
6. Nutritional Status and Its Impact on Treatment Tolerance in Non-Small-Cell Lung Cancer Patients Receiving Osimertinib. Read the study on PubMed