Medical Oncologist
Diet and nutrition myths
Does Sugar — Feed Cancer?
The fear that eating sugar feeds your cancer is one of the most common questions patients and families ask. The short answer is that cutting sugar from your diet will not starve your cancer. Understanding why requires a quick look at how cancer actually uses energy.
Medically reviewed by Dr. Bharati Devi Gorantla, Medical Oncologist, MBBS · MD · DM (Adyar, Chennai) · ECMO · MRCP SCE (UK) · Last reviewed August 2026
- All cells use glucose — Every cell in your body — including cancer cells — runs on glucose. This is not unique to cancer.
- Cutting sugar does not starve tumours — No clinical trial has shown that removing sugar from the diet stops or slows cancer growth in people.
- Malnutrition is the real risk — Severely restricting carbohydrates during treatment can cause malnutrition, which makes treatment harder to tolerate.
- Overall diet quality does matter — Limiting ultra-processed food and maintaining a healthy weight is sensible — but for different reasons than 'sugar feeds cancer'.
17+
Cancer Specialists
on Panel
on Panel
96.9%
Breast Cancer
Survival Rate*
Survival Rate*
15,000+
Patients
Treated
Treated
4.8★
Google Rating
(800+ reviews)
(800+ reviews)
All cells in your body — including cancer cells — use glucose for energy. This does not mean eating sugar makes cancer grow faster. No clinical trial has shown that cutting sugar starves cancer. What matters during treatment is eating enough of the right foods, not eliminating an entire fuel source.
Why do people say sugar feeds cancer — and is it true?
Every cell runs on glucose
Your brain, heart, immune cells and cancer cells all use glucose as fuel. This is basic metabolism, not something unique to cancer. Rapidly dividing cells consume more glucose than resting cells because growing takes energy.
PET scans created a misunderstanding
A PET scan uses radioactive glucose to find cancer. Tumours appear bright on the scan because they are growing fast and taking up more fuel. Some people read this to mean that sugar causes cancer to grow — but the logic runs the other way. Cancer takes up more glucose because it is already growing, not because it has been fed sugar.
Cancer cells metabolise glucose differently — but this cannot be exploited by cutting sugar
Cancer cells process glucose in an unusual way even when oxygen is available — a finding called the Warburg effect. Researchers are studying this. But laboratory observations about cell metabolism do not translate directly into a dietary recommendation for people in treatment.
Cutting sugar has not been shown to slow cancer in people
WCRF, ASCO and ESMO do not recommend eliminating sugar or carbohydrates as a cancer treatment. Clinical trials have not shown that doing so affects tumour growth in people.
What the evidence does support
Excess body weight and chronically raised insulin are associated with higher risk of several cancers. Limiting added sugars and ultra-processed food is sensible for overall metabolic health. This is not the same as saying eating sugar makes cancer grow.
Should you stop eating rice, roti and fruit?
No. Rice, roti, dal and whole fruit are not the same as refined sugar or ultra-processed food. They provide fibre, vitamins, minerals and energy that your body needs — especially during treatment.
Many patients in India restrict these staple foods severely after a diagnosis and end up not eating enough. That is a real harm. Malnutrition makes chemotherapy and radiotherapy harder to tolerate and recovery slower.
If you are worried about specific foods, ask for a referral to a registered dietitian who works with cancer patients. The goal during treatment is eating well, not eating less.
Is there any real link between sugar and cancer?
There is a link — but it is indirect. Diets high in added sugar and ultra-processed food over many years can contribute to obesity and insulin resistance. Both are associated with increased risk of several cancers, including colorectal, breast and endometrial cancer.
This is a factor in cancer development over time, not a mechanism by which eating sugar makes existing cancer grow faster.
WCRF and IARC recommend limiting added sugars and ultra-processed food as part of cancer prevention — alongside physical activity and maintaining a healthy weight. This guidance applies to prevention, not to treating cancer that is already present.
Meet the Specialists
17+ senior cancer specialists. One panel for your case.
Trained at AIIMS, Tata Memorial, and leading international centres. Combined 150+ years of experience. Every complex case is reviewed by 3+ of them — together.
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
Medical Oncologist
Medical Oncologist
Surgical Oncologist
Dr. Muralidhar Muddusetty
MBBS (AIIMS), MS (Surgery) (AIIMS), DNB (Surgical Oncology), MRCS (Edinburgh)
Surgical Oncologist
Surgical Oncologist
Surgical Oncologist
Dr. Vinay Mamidala
MBBS, MS(General Surgery), M.Ch(Surgical Oncology), FMAS, FARIS(Ongoing)
Surgical Oncologist
Radiation Oncologist
Radiation Oncologist
Radiation Oncologist
Hematologist
Interventional Radiologist
Dr. Mohammed Imran
Surgical Oncologist
Dr. Vajja Sandeep Kumar
MBBS, MS (General Surgery), DrNB (Surgical Oncology), FALS Oncology
Surgical Oncologist
Want a specific doctor for your case? Mention them when booking.
Book Free ConsultationBook an appointment with our specialist
Share your name and number — we'll call you back within 30 minutes to schedule your consultation.
You do not have to work this out alone
A 45-minute consultation with a specialist who treats this every week.
Could restricting carbohydrates harm you during treatment?
Yes, it can. Malnutrition during cancer treatment is one of the factors most consistently associated with worse outcomes. Patients who eat too little tolerate chemotherapy and radiotherapy less well and take longer to recover.
During treatment, your body needs enough energy and protein to repair tissue, support your immune system and get through side effects. Cutting a major fuel source without medical guidance risks making this worse.
Tell your oncology team what you are eating and what you have stopped eating. If you are losing weight without meaning to, ask to be referred to a cancer dietitian.
What about specific foods — rice, fruit, jaggery and coconut water?
Is jaggery safer than sugar for someone with cancer?
Jaggery is made from sugarcane and its main component is still sucrose. It contains small amounts of iron and minerals that refined white sugar does not, but it is metabolised in the same way. Replacing white sugar with jaggery is not harmful, but it will not protect you from cancer or affect how your treatment works. If you prefer jaggery for taste or cultural reasons, that is fine — just do not assume it changes your cancer risk or outcome.
What about fruit? Mangoes, bananas and chikoo are very sweet.
Whole fruit contains fructose alongside fibre, antioxidants, vitamins and water. The fibre slows absorption of sugar into your bloodstream — very different from drinking the same sugar dissolved in a soft drink. Avoiding fruit entirely during cancer treatment can deprive you of nutrients that support your immune system and recovery. WCRF and ESMO nutritional guidance includes whole fruit as part of a healthy diet for people with cancer. There is no guidance recommending its removal.
Should I stop having coconut water?
Coconut water contains natural sugars alongside electrolytes — potassium, sodium and magnesium — that are useful when you are dealing with nausea, vomiting or diarrhoea from treatment. There is no evidence it harms cancer outcomes, and during periods of poor intake it can help maintain hydration. If you have kidney involvement or are on certain medications that affect potassium levels, check with your team before drinking large amounts. That caution is about the potassium in a medical context, not the sugar.
I read that a ketogenic diet can starve cancer. Should I try it?
Ketogenic diets — very high in fat, very low in carbohydrates — are being studied as a possible adjunct to treatment in some cancer types. The research is at an early stage and results are not yet consistent. NCCN, ASCO, ESMO and WCRF do not recommend a ketogenic diet as a standard cancer treatment. Starting one without guidance is risky during active treatment: it is difficult to maintain adequate calorie intake, and the restriction can worsen fatigue, nausea and muscle loss at a time when your body already has very high energy demands.
If sugar is not the problem, what should I actually change in my diet?
Focus on what the evidence consistently supports: eat a variety of vegetables, pulses and whole grains; include adequate protein from dal, eggs, chicken, fish or paneer; limit ultra-processed packaged food, fried snacks and drinks with added sugar; and maintain enough overall intake to keep your weight stable during treatment. If you are losing weight, increasing calories is the priority — not reducing them. A cancer dietitian can give you a plan that fits your treatment, your side effects and what your family normally cooks.
Did you know?
Malnutrition is one of the most common and preventable complications of cancer treatment. Patients who eat too little during chemotherapy or radiotherapy are more likely to need dose reductions, treatment breaks and unplanned hospital admissions.
The greatest nutritional risk for most people with cancer is not eating too much sugar — it is not eating enough.
Source: ESMO Clinical Practice Guidelines: Nutritional Support in Cancer
Explore 113 more Family, Fertility, Diet & Emotional Wellbeing topics
Diet, Nutrition & Complementary Therapy
- Ayurveda Alongside Targeted Therapy: An Honest Assessment
- Do Immunity Boosters Help During Cancer Treatment?
- Does Sugar Feed Cancer? Separating Myth From Fact
- Eating With Mouth Sores: Foods That Don't Hurt
- Eating to Control High Blood Sugar From Cancer Drugs
- Food Safety and Hygiene for Cancer Patients at Home
- Foods to Avoid on Targeted Therapy
- How Much Protein Does a Cancer Patient Actually Need?
- Hydration: How Much Water and What Counts
- Is Cow's Milk, Soya or Non-Veg Food Safe During Cancer Treatment?
- Keto and Intermittent Fasting During Cancer Treatment: Is It Safe?
- Managing Weight Loss and Muscle Wasting
- What Should You Eat While on Targeted Therapy? A Practical Indian Diet Guide
- What to Eat When You Have Diarrhoea From Cancer Tablets
- Yoga and Pranayama During Cancer Treatment
Caregiver Enablement
- Building a Care Roster When One Person Can't Do It All
- Caregiver Burnout: Recognising It Before It Breaks You
- Caregiver Red Flag Chart: When to Take Them to Hospital
- Caring for an Elderly Parent on Oral Cancer Tablets
- Cooking for Someone on Targeted Therapy: A Kitchen Guide
- Coordinating Care From Abroad: A Guide for NRI Families
- Financial Management for Caregivers: Bills, Claims and Records
- How to Get a Second Opinion Without Offending Your Doctor
- How to Track Side Effects: A Simple Daily Diary System
- Managing Medicines, Refills and Pharmacy Runs
- Questions Every Caregiver Should Ask at the Oncology Visit
- Supporting Someone Emotionally Without Saying the Wrong Thing
- The Complete Caregiver's Guide to Targeted Therapy
- What to Do When the Patient Refuses to Take Their Medicine
Fertility, Pregnancy & Sexual Health
- Accidental Pregnancy While on Targeted Therapy: What Now?
- Can You Breastfeed While on Targeted Therapy?
- Cancer Diagnosed During Pregnancy: Can Targeted Therapy Be Used?
- Contraception on Targeted Therapy: Which Methods Are Safe?
- Early Menopause Caused by Cancer Treatment
- Erectile Dysfunction and Sexual Changes in Men on Treatment
- Fertility After Long-Term Targeted Therapy: What the Data Shows
- Fertility Preservation Before Starting Treatment: Your Options and Timeline
- How Long Must You Wait Before Trying to Conceive?
- Sperm Banking Before Cancer Treatment: A Practical Guide
- Talking to Your Partner About Sex During Cancer Treatment
- Vaginal Dryness, Pain and Low Libido During Treatment
- Will Targeted Therapy Affect My Fertility?
Genetic Predisposition & Family Risk
- BRCA Testing in India: Cost, Process and Where to Get It Done
- Cascade Testing: Getting Your Family Members Tested
- Coping With the Anxiety of a Positive Genetic Test
- Does a BRCA Mutation Mean You Will Definitely Get Cancer?
- Family History of Cancer: Should You Get Genetic Testing?
- Genetic Counselling: What Actually Happens in the Session
- Hereditary Diffuse Gastric Cancer and the CDH1 Gene
- How to Tell Your Children and Siblings About a Genetic Risk
- I'm BRCA Positive but Have No Cancer: What Happens Now?
- IVF and Preimplantation Testing to Avoid Passing On a Mutation
- Li-Fraumeni Syndrome: Living With a TP53 Mutation
- Lynch Syndrome: Cancers, Screening and Treatment Implications
- MEN2, VHL and Other Endocrine Cancer Syndromes
- MUTYH, PALB2, ATM and CHEK2: Moderate-Risk Genes Explained
- Male BRCA Carriers: The Risks Nobody Talks About
- PARP Inhibitors: How a Genetic Mutation Becomes a Treatment Advantage
- Risk-Reducing Mastectomy: How to Decide
- Risk-Reducing Ovary and Tube Removal: Timing and Consequences
- Somatic Mutation Found on NGS: Could It Be Inherited?
- Surveillance Instead of Surgery: What Screening Looks Like
- Which Family Histories Actually Suggest a Hereditary Cancer Syndrome?
- Will a Genetic Test Result Affect Your Insurance in India?
Mental Health & Emotional Wellbeing
- Body Image When Your Skin, Nails and Hair Change
- Cancer Support Groups in India: How to Find One
- Depression During Long-Term Cancer Treatment
- Handling Unhelpful Advice and Toxic Positivity
- Living With Cancer as a Chronic Disease: A New Identity
- Sleep, Anxiety and Night-Time Fear During Treatment
- Talking to Your Children About Your Cancer Diagnosis
- Telling Friends, Relatives and Neighbours: How Much to Share
- The Fear That the Drug Will Stop Working: How to Live With It
- When Should You See a Psycho-Oncologist?
Myths, Misinformation & Verification
- Are Generic Cancer Drugs Fake or Weaker?
- Can Cancer Be Cured Without Any Modern Medicine?
- Cannabis and CBD Oil for Cancer: What the Evidence Actually Says
- Does Soursop, Apricot Seed or Alkaline Water Cure Cancer?
- Does a Biopsy Spread Cancer?
- How to Fact-Check Cancer Information You Read Online or From AI
- Miracle Cancer Cures on WhatsApp and YouTube: How to Spot a Fake
- Myth: Cancer Treatment Is Worse Than the Disease
- Myth: If the Scan Is Clear You Can Stop the Tablets
- Myth: Positive Thinking Cures Cancer
- Myth: Sugar, Milk or Non-Veg Food Feeds Cancer
- Myth: Targeted Therapy Has No Side Effects
- Myth: Targeted Therapy Is Only for the Rich
Palliative Care & End of Life
- Breathlessness and Comfort Care in Advanced Cancer
- Hospice and Home Palliative Care Services in India
- How to Have a Goals-of-Care Conversation With Your Doctor
- Pain Control at Home: What's Possible and What to Ask For
- Palliative Care Is Not Giving Up: Clearing the Biggest Myth
- Should You Ask How Long You Have Left?
- Supporting a Family Member in Their Last Months
- What 'Best Supportive Care' Actually Means
- When Is It Right to Stop Cancer Treatment?
Special Populations & Comorbidities
- Cancer Treatment After an Organ Transplant
- Cancer Treatment for Patients on Dialysis
- Cancer Treatment in Patients With Past or Active Tuberculosis
- Growth, Puberty and School During Childhood Cancer Treatment
- Hepatitis B and C Reactivation Risk During Cancer Treatment
- Managing Diabetes While on Targeted Therapy
- Obesity, Underweight and Dosing: Does Body Size Change the Dose?
- Paediatric Targeted Therapy: What Parents Need to Know
- Targeted Therapy With Autoimmune Disease
- Targeted Therapy With Chronic Kidney Disease
- Targeted Therapy With Existing Heart Disease
- Targeted Therapy With Liver Disease or Cirrhosis
- Targeted Therapy for Adolescents and Young Adults
- Targeted Therapy for Patients With Mental Illness or Dementia
- Targeted Therapy in HIV-Positive Patients
- Targeted Therapy in Patients Over 75: Is It Worth It?
- Treating Patients With Poor Performance Status
Next step
Still not sure what applies to you?
Send your reports across and a senior medical oncologist will go through what they mean, what is known, and what the options actually are.
Common questions
Frequently asked questions
If I completely stop eating sugar, will it help my cancer treatment?
No. There is no evidence that stopping sugar improves treatment outcomes. What can happen when patients cut sugar and carbohydrates severely is that they stop eating enough — and malnutrition makes treatment harder to tolerate, not easier. Your oncology team needs you to be well-nourished. Reducing added sugars and ultra-processed food as part of eating better overall is a sensible goal — just do not let it become a reason to eat far less.
Why do PET scans use glucose if sugar does not feed cancer?
PET scans use radioactive glucose to locate cancer because rapidly dividing cells take up more glucose than resting cells. This makes the scan useful for detecting and staging. It does not mean that eating glucose causes cancer to grow. The scan is exploiting an existing property of fast-growing cells, not demonstrating that diet changes growth rate. Many normal cells — including brain cells — also take up glucose actively and appear bright on a PET scan.
Is there any cancer where diet really does make a difference?
Diet is a factor in cancer prevention. Diets high in processed meat, ultra-processed food and excess calories are associated with higher risk of colorectal, breast and endometrial cancers over time, according to WCRF and IARC research. During treatment, diet affects how well you tolerate side effects and how quickly you recover. Neither is the same as sugar causing existing cancer to grow. Speak to your oncologist or a registered dietitian about what applies to your specific diagnosis.
My family wants to cook without any sugar at all. Should I let them?
A home-cooked diet with less added sugar and fewer ultra-processed foods is a healthy pattern, and there is nothing wrong with your family wanting to support you this way. The concern is when this turns into restricting staple foods — rice, roti, dal, fruit — so much that you stop eating enough overall. Make sure meals still provide enough energy and protein. If your weight is falling or you are struggling to eat during treatment, tell your team.
Can I ask my oncologist about a specific diet I have read about online?
Yes, and you should. Bring details of what you have read — the name of the diet, who recommends it and what it involves. Your oncologist or a cancer dietitian can tell you whether it is safe given your specific treatment, side effects and nutritional status. No diet plan recommended online should be started during active cancer treatment without a clinical review first. This includes ketogenic, alkaline, raw food and fasting protocols.