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Claim 05 · Cancer

Sugar: "cancer feeds on it, so cutting sugar starves tumours".

Three sugar cubes set apart from a single cell Three sugar cubes stand in a row on the left. A single cell with its nucleus sits apart on the right. Cutting sugar does not starve a tumour; the link runs through body fat.

As forwarded

"Cancer feeds on sugar, so cutting sugar starves tumours."

Common in Hindi and English WhatsApp forwards and "cancer diet" videos, often citing the Warburg effect. A specific widely shared version with URL: not available. Reach not available

Verdict

Exaggerated

Cancer cells do use a lot of glucose, but so do your brain and muscles; you cannot starve a tumour by cutting sugar, and crash diets can harm patients. Cutting added sugar matters because it helps control weight, and excess body fat is linked to at least 13 cancers.

What the evidence says

Supported

What is right. Cancer cells grow fast and consume glucose, often by the inefficient "Warburg" pathway. Cancer Research UK acknowledges this and notes the pathway is being studied as a possible drug target, but describes those approaches as experimental. [S1]

Exaggerated

Where it goes wrong. The body cannot direct glucose only to tumours; healthy cells need it too, and cancer cells also use amino acids and fats. CRUK: "There's no evidence that following a 'sugar-free' diet lowers the risk of getting cancer", and very low-carbohydrate diets can harm patients who need adequate nutrition during treatment. [S1]

Established

The real link runs through body fat. The IARC Working Group reviewed more than 1,000 epidemiological studies and found sufficient evidence that excess body fatness raises the risk of 13 cancers: oesophageal adenocarcinoma, gastric cardia, colorectum, liver, gallbladder, pancreas, postmenopausal breast, endometrium, ovary, kidney, meningioma, thyroid and multiple myeloma. [S2] CRUK describes overweight and obesity as the biggest cause of cancer after smoking. [S1]

What to do instead

  1. Anyone with a cancer diagnosis: do not start a restrictive or "no sugar" diet without the treating oncologist and a dietitian; under-nutrition slows recovery. Patients on treatment should never fast or cut food groups without their oncology team, and "sugar-free" claims are not a reason to delay or refuse chemotherapy, surgery or radiotherapy. [S1]

  2. Everyone: cut free sugars, starting with sugary drinks; keep sweets, cakes and biscuits occasional; check labels on cereals, sauces and flavoured yoghurts. The goal is a healthy body weight, which is where the cancer-risk benefit lies. [S1][S2]

  3. Whole fruit is not the target; free (added) sugars and sugary drinks are. [S1]

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Sources

  1. S1
    Cancer Research UK. Sugar and cancer: what you need to know.Tier 4-equivalent charity science page · reviewed August 2023
    news.cancerresearchuk.org/2023/08/16/sugar-and-cancer-what-you-need-to-know
  2. S2
    Lauby-Secretan B et al. (IARC Working Group). Body fatness and cancer: viewpoint of the IARC Working Group. NEJM 2016;375:794–798.Tier 3 / IARC Tier 2 · 2016
    pmc.ncbi.nlm.nih.gov/articles/PMC6754861
  3. S3
    World Cancer Research Fund. Continuous Update Project: energy balance and body fatness.Tier not graded in the research file · PDF returned binary data; not opened
    wcrf.org/resources/energy-balance-and-body-fatness

Tiers are as graded in the research file. "Circulation only" sources document that a claim circulates and are never cited as evidence. Where a primary paper could not be opened, the page says so in the Honest note.

Reviewed by

Medical review: being arranged

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