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What people eat, weigh and do shapes who gets cancer and how treatment goes. Decades of trials separated what is established (obesity, alcohol and inactivity cause cancer; exercise after treatment reduces recurrence) from what is hype, and the next questions are being asked with the rigour of a drug trial.
Epidemiology established the causes: tobacco, then excess body fat (now linked to at least thirteen cancers), alcohol, processed meat and physical inactivity. The first generation of intervention trials mostly disappointed. A vegetable-rich diet did not reduce breast cancer recurrence (WHEL), vitamin D and fish oil did not prevent cancer (VITAL), fish oil did not slow cachexia, and high-dose vitamin C did not treat anything. Those null results are as valuable as positive ones: they are why this front can tell evidence from marketing.
The breakthrough came from exercise. In 2025 the CHALLENGE trial showed that a coached, structured exercise programme after colon cancer treatment reduces recurrence and improves survival, the first randomised proof that a lifestyle intervention changes a hard cancer outcome. Nutrition care during treatment has its own evidence base: malnutrition screening, dietitian-led therapy, enhanced recovery around surgery and prehabilitation are all in guidelines. The live scientific questions are the gut microbiome's effect on immunotherapy, whether GLP-1 agonists and bariatric surgery prevent cancer, whether fasting or ketogenic diets help around treatment, and how to treat cachexia as a disease.
The pace is set by the absence of a commercial sponsor for anything that cannot be patented, by misinformation that fills the gap, and by health systems that do not pay for exercise or dietetics the way they pay for drugs.
Cohort studies and IARC's monographs built the list that is no longer in dispute: tobacco, alcohol (a group 1 carcinogen for at least seven cancers), processed meat, and excess body fat, which IARC linked to thirteen cancers in 2016. Physical inactivity and sugary drinks joined through the same evidence. The World Cancer Research Fund's Continuous Update Project keeps the grading current, which is why this front can say 'convincing', 'probable' or 'insufficient' rather than 'linked to'.
Three thousand breast cancer survivors coached for years to eat far more vegetables had no fewer recurrences (WHEL). Vitamin D and fish oil did not prevent cancer in 25,000 people (VITAL). Fish oil did not slow cancer wasting. High-dose vitamin C failed twice in randomised trials at the Mayo Clinic. Each null result closed a question that supplements marketing keeps open, and together they set the standard: a diet claim needs a randomised trial with a cancer endpoint.
CHALLENGE randomised nearly 900 people after colon cancer treatment to a three-year coached exercise programme or health education and, in 2025, reported fewer recurrences and fewer deaths in the exercise arm: the first randomised proof that a lifestyle intervention changes a hard cancer outcome. Exercise during chemotherapy is safe and reduces fatigue; four weeks of prehabilitation before major surgery cuts complications (PREHAB); enhanced recovery protocols replaced pre-operative fasting. The question is no longer whether but how to prescribe, deliver and pay for it.
Weighing every patient, screening for malnutrition, dietitian-led counselling and, when needed, tube or intravenous feeding are in ESPEN and ASCO guidelines because malnutrition predicts toxicity, complications and death. Immunonutrition before major surgery, a Mediterranean pattern for survivors, and dietitian-led weight loss in hormone-positive breast cancer (the 3,000-patient BWEL trial is awaited) are the evidence-based options. Soy is safe; most supplements are unnecessary and some interact with treatment.
Patients who eat plenty of fibre and avoid unnecessary antibiotics respond better to checkpoint inhibitors in observational studies, and small trials of faecal microbiota transplantation from responders or healthy donors converted some non-responders into responders (Pittsburgh, MIMic-01). Defined bacterial consortia and stewardship of antibiotics around immunotherapy are the next tests. This is the one area of nutrition where a mechanism, the gut's training of the immune system, is being tested in randomised trials with response as the endpoint.
People taking GLP-1 agonists for obesity have lower rates of obesity-related cancers in observational data, and bariatric surgery patients develop fewer cancers, but neither has a randomised trial with cancer as the primary outcome; that trial is the most important one this front could run. Fasting-mimicking diets around chemotherapy, ketogenic diets in glioblastoma (ERGO2 is the only randomised test) and time-restricted eating have plausible mechanisms and small trials. GLP-1 drugs to reverse endometrial precancer in women with obesity is the nearest practical application.
Cancer wasting is driven in part by the hormone GDF-15, and the first antibody against it (ponsegromab) improved weight and physical activity in phase 2. Low-dose olanzapine restored appetite in a Tata Memorial trial for pennies; resistance training and protein remain the foundation. The proposal is to treat cachexia like sepsis, with a trigger, a bundle and an audit, and to combine the new antibody with exercise and nutrition rather than test it alone.
CHALLENGE proved exercise works in one cancer at one dose; dose-finding trials across cancers, reimbursement of supervised programmes as treatment, and delivery at population scale are the next decade's work. Half of people with cancer sleep badly, and trials are asking whether treating insomnia and restoring circadian rhythm changes outcomes. Evidence-based integrative oncology in every centre is the proposed bridge that meets patient demand without ceding ground to unproven regimens.
Nothing on this front can be patented, so trials depend on public and charitable funders and are rare; misinformation fills the space with alkaline diets and juice cures; health systems pay for drugs but not for dietitians or exercise physiologists; and the prevention measures already proven (alcohol pricing and labelling, sugar taxes, active travel) are politically harder than any drug approval. Cancer warning labels on alcohol, evaluated as a natural experiment, would be a start.
Every era's records, trial outcomes and papers, and every watch item, as JSON.
Probability ranges are named estimates that the claim is borne out on roughly a five-year horizon. They are meant to be argued with: propose a revision with your name and reasoning via a pull request to src/data/confidence.ts.
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Shares Dietary pattern scores (Mediterranean, HEI, AHEI, DASH, WCRF/AICR), WHEL (Women's Healthy Eating and Living), Fasting and fasting-mimicking diets around chemotherapy, Metabolic syndrome and insulin resistance.
Shares Fund structured exercise after colon cancer surgery as a treatment, because a randomised trial says it works as well as a drug, Combine the new anti-wasting antibody with exercise and protein, Pay for supervised exercise the way we pay for drugs, Structured exercise prescribed like a drug in all curative-intent cancer care.
Shares Ponsegromab phase 2 in cancer cachexia, Dietitian-led weight-loss programmes in HR-positive breast cancer, Resistance training and protein for cachexia and sarcopenia, GLP-1 receptor agonists and obesity-related cancer risk.
Shares Combine the new anti-wasting antibody with exercise and protein, Cachexia-directed therapy (GDF-15 blockade), Resistance training and protein for cachexia and sarcopenia, Sarcopenia.
Shares Metabolic syndrome and insulin resistance, Warburg-effect diet claims ('sugar feeds cancer'), Time-restricted eating in cancer prevention and survivorship, Ketogenic diets in glioblastoma.
Shares A trial of GLP-1 weight-loss drugs with cancer as the primary outcome, BWEL (Breast Cancer Weight Loss, Alliance A011401), Dietitian-led weight-loss programmes in HR-positive breast cancer, Resistance training and protein for cachexia and sarcopenia.
Shares ERGO2: ketogenic diet and fasting during re-irradiation of recurrent glioma, Warburg-effect diet claims ('sugar feeds cancer'), Ketogenic diets in glioblastoma, Unproven diet claims (alkaline, juice, 'anti-cancer' diets).
Shares Immunonutrition before cancer surgery, Four weeks of training and nutrition before major cancer surgery, as standard, PREHAB: multimodal prehabilitation before colorectal cancer surgery, Enhanced recovery (ERAS) and perioperative nutrition.