1. Refined carbohydrates
Are grain-based foods that have been heavily processed, making them less nutritious but more appealing. Common examples include bread, crackers, cereal, pasta, pretzels, rice cakes, and granola bars.
These foods quickly convert to sugar (glucose) in the bloodstream, giving them a high glycemic index. Research shows that diets high in glycemic load are linked to increased cancer risk, higher recurrence rates, and lower survival.
When energy is low, foods like pasta or cereal may feel convenient, but they don’t support healing or recovery, and may even work against it. The impact can be reduced by adding fibre and pairing carbohydrates with protein and healthy fats, which helps slow blood sugar spikes and lessen their effect on the body.
2. Trans fats and reheated frying oils
Not all fat is bad. In fact, some fats support healing, even during cancer recovery. The problem is that many common “comfort” fats do more harm than good.
The fats worth limiting are partially hydrogenated oils — the source of artificial trans fats, now restricted in many countries — and oils that have been repeatedly reheated for deep frying, which accumulate oxidation products. Both turn up in fried takeaway food, packaged baked goods and some margarines.
A correction worth making: ordinary seed and vegetable oils — canola, corn, soybean, sunflower, safflower — are often lumped in with those, and the evidence does not support it. The American Heart Association states there is no reason to avoid them, and reviews of omega-6 intake have not found they raise inflammation in humans. An earlier version of this article repeated the “seed oils are inflammatory” claim. It was wrong, and we have corrected it.
While fried foods and chips are obvious sources, these oils also hide in processed foods like salad dressings, sauces, breads, and crackers. The best way to avoid them is to read labels and limit processed foods.
3. Added sugar
Sugar fuels cancer growth.
It’s often used for comfort during stress or illness, but sugar interferes with the body’s ability to heal and recover from cancer.
Sugar promotes cancer by increasing inflammation, feeding cancer cells through glucose, raising insulin levels, and suppressing the immune system. High blood sugar creates an environment where cancer cells grow, survive, and spread more easily.
Cravings are real-but choosing alternatives that stabilize blood sugar can better support healing and recovery.
4. Processed meat
Research on animal foods and cancer is mixed, but one thing is clear: processed meats are the most concerning. These are meats like pork or beef that are salted, cured, or smoked.
Processed meats contain cancer-linked compounds such as nitrates, heterocyclic amines (HCAs), and polycyclic aromatic hydrocarbons (PAHs). Common examples include bacon, sausage, salami, pepperoni, ham, and beef jerky.
While they’re often quick comfort foods during stressful times, relying on processed meats for protein -especially during treatment- it can do more harm than good.
* *No material on this post is intended to be a substitute for professional medical advice, diagnosis or treatment. It is for informational purposes only and should not be considered professional medical advice. Always consult a doctor.
Sources
- “Nutrition and Physical Activity Guideline for Cancer Survivors”, American Cancer Society.
- “Carcinogenicity of the consumption of red meat and processed meat”, World Health Organization / IARC — processed meat classified Group 1, 2015.
- “Diet, activity and cancer”, World Cancer Research Fund.
- “There’s no reason to avoid seed oils and plenty of reasons to eat them”, American Heart Association, 2024.
This article is general information, not medical advice, and it has not been reviewed by a clinician. Nutrition needs during and after cancer treatment vary enormously depending on the cancer, the treatment and the person. Talk to your oncology team or a registered oncology dietitian before changing your diet. Nothing here should delay or replace their guidance.
Researched and written by Victor Ramirez. Edited and fact-checked by Mia Alejandra Umphrey. Drafting assisted by AI; all facts verified against the sources above before publication. See our editorial standards.
Updated 27 July 2026: corrected an inaccurate claim that seed oils are inflammatory, removed a Wikipedia citation, and reframed the section headings.
