No; although cancer cells use more glucose than healthy cells, no study has shown that eating sugar makes cancer worse or that cutting out sugar makes cancer shrink or disappear [1]. Even so, a high-sugar diet can lead to weight gain, and obesity is linked to a higher risk of at least 13 types of cancer [1, 2]. So the right advice is to limit free sugars (for most adults, less than about 12 teaspoons a day), not to cut out healthy foods altogether [3].
Where does this belief come from?
Research has shown that cancer cells use more glucose (sugar) than normal cells. This has led some people to think that eating sugar directly "feeds" a tumour. But no study has shown that eating sugar makes cancer worse, or that if you cut out sugar, cancer will shrink or disappear [1].
| Belief | What the evidence says |
|---|---|
| Sugar in food feeds the tumour, and the patient must cut out sugar completely | No study has shown that eating sugar makes cancer worse, or that cutting it out makes cancer shrink [1] |
| Sugar has nothing to do with cancer | A high-sugar diet can lead to weight gain, and obesity is linked to a higher risk of several types of cancer [1, 2] |
| Sweet drinks and fruit juice are harmless | In a large study, drinking sweet drinks and even natural fruit juice was linked to a higher risk of cancer [4]; sweet drinks are also linked to weight gain [7] |
| Fruit is forbidden because of its natural sugar | Fresh fruit and vegetables are excellent choices; what should be limited is free sugars, including the sugar in fruit juice [3] |
The evidence on sugar and the risk of cancer
Most of the evidence is about the risk of getting cancer, not the growth of a tumour that is already there:
- Sugary drinks: in a study of more than 100,000 French adults, those who drank one small glass (100 mL) more of sugary drinks a day developed slightly more cancer; drinks with artificial sweeteners did not show this link. The authors say this result needs to be repeated in other studies [4].
- A review of all the evidence: high sugar intake was linked to several bad outcomes, including some cancers; but the quality of most of this evidence is low [7].
- Obesity: after reviewing more than a thousand studies, the International Agency for Research on Cancer concluded that excess body fat raises the risk of cancers of the womb, oesophagus, stomach, liver, kidney, pancreas, bowel, gallbladder, breast (after the menopause), ovary, thyroid and several others [2].
The American Society of Clinical Oncology says there is very little evidence for special diets or deliberate weight loss during treatment [5]. Chemotherapy and radiotherapy can make eating hard, and keeping your weight up and eating enough energy and protein matter; if you have trouble eating, talk to your doctor, nurse or a dietitian [6, 8] (Nutrition during treatment).
Related questions
Should I give up fruit too?
No. The World Health Organization considers fresh fruit and vegetables an excellent choice; but fruit juice, even without added sugar, contains a lot of sugar and should be limited [3].
What about artificial sweeteners?
In the French study, drinks with artificial sweeteners were not linked to cancer [4].
How much sugar a day is allowed?
The World Health Organization recommends keeping added sugars and fruit juice below a limit; for someone eating about 2000 calories a day, that means about 50 grams (about 12 teaspoons). Cutting this in half probably gives extra benefit [3].
Related cancer types
Related questions
References
8 referencesShow all references, 3 with a study cardClose the reference list
Numbers in the text, such as [1], refer to these sources. Sources with a “Study card” button are summarised in the site’s evidence library.
- 1
- 2
- 3
- 4
- 5Exercise, Diet, and Weight Management During Cancer Treatment: ASCO Guideline
- 6Chemotherapy to Treat Cancer
- 7Dietary sugar consumption and health: umbrella review
- 8Radiation Therapy to Treat Cancer
This page is based on reputable scientific sources and was last updated on 28 October 2026. The content of this website is for educational and informational purposes only and does not replace consultation, diagnosis or treatment by a specialist physician. Consult your treating physician about any treatment decision.
Printed from the website; the full and up-to-date version: https://drdabiri.com/en/questions/does-sugar-feed-cancer/