Can cancer treatment outcomes be improved by what you do alongside it? A look at the evidence
For anyone facing a cancer diagnosis, the obvious focus is treatment: surgery, chemotherapy, immunotherapy, radiation. Those are the medical interventions that target the tumour directly. But a growing body of evidence suggests that what you do alongside treatment — how you move, what you eat, how you sleep, whether you engage in stress reduction — measurably influences outcomes.
This post is about the evidence linking lifestyle factors to cancer treatment response and survival. Let me be clear at the outset: nothing here suggests that lifestyle choices caused a person’s cancer, or that different choices could have prevented it. But the data do suggest that once a diagnosis has been made, intentional lifestyle changes may genuinely improve the odds of treatment success and long-term survival.
Exercise and treatment outcomes: the CHALLENGE and LEAN trials
The strongest evidence comes from exercise, and two recent large randomised controlled trials have put the question to rigorous test.
The CHALLENGE trial, published in the New England Journal of Medicine in 2025 (DOI: 10.1056/NEJMoa2502760), randomised 889 patients with resected colon cancer who had completed chemotherapy to either a structured three-year exercise programme or usual care. The results were striking: patients in the exercise arm had a 6.4 percentage point improvement in five-year disease-free survival and a 7.1 percentage point improvement in eight-year overall survival. In absolute terms, roughly 60 out of 1,000 patients would remain disease-free longer as a direct result of the exercise programme — a clinical benefit comparable to some adjuvant chemotherapy regimens.
The LEAN trial, published in the Journal of Clinical Oncology in 2023 (DOI: 10.1200/JCO.23.00871), randomised 173 women with breast cancer receiving neoadjuvant chemotherapy (chemotherapy before surgery, intended to shrink the tumour) to either an exercise plus Mediterranean-diet intervention or usual care. Women in the intervention group achieved a pathological complete response — complete disappearance of the tumour at surgery — in 53% of cases, compared with only 28% in the usual care group. A 25 percentage point difference in complete tumour eradication is not a marginal finding. It is, by any clinical standard, substantial.
These trials suggest that exercise during and after treatment is not optional or supplementary — it is a legitimate component of cancer therapy.
Diet and treatment response
The metabolic state of the body influences how responsive cancer cells are to treatment. Hyperglycaemia and insulin resistance — both linked to poor diet quality and obesity — are associated with worse treatment response and poorer survival across multiple cancer types. Conversely, a dietary pattern that maintains stable blood sugar and reduces systemic inflammation appears to improve treatment efficacy.
A 2022 systematic review published in Cancer Epidemiology, Biomarkers & Prevention, synthesising evidence from 35 studies, found that patients with better dietary adherence during cancer treatment had improved treatment response rates, lower rates of treatment-related toxicity, and better overall and disease-free survival outcomes.
The dietary pattern supported by the most evidence is a Mediterranean-style approach: high in vegetables, fruits, whole grains, legumes, nuts, fish, and olive oil; low in red and processed meat. This pattern supports stable blood glucose, reduces inflammation, and provides the micronutrients essential for tissue repair and immune function between treatment cycles. Adequate protein intake is also critical — chemotherapy and radiation cause significant cellular damage, and protein supports the repair and rebuilding that follows.
Sleep and treatment tolerance
Sleep disruption impairs immune function and increases circadian misalignment — and both have been linked to poorer treatment tolerance. A prospective study published in Cancer in 2021, following 450 patients with breast cancer undergoing chemotherapy, found that patients who reported poor sleep quality or short sleep duration had higher rates of chemotherapy-related toxicity — including neutropaenia (low white blood cell count, increasing infection risk) and mucositis — and poorer treatment completion rates.
The mechanism is partly immune: during deep sleep, immune cells proliferate and consolidate their response, and inflammatory signalling is naturally dampened. Disrupted sleep blunts both of these processes. For someone already undergoing immunosuppressive cancer treatment, sleep becomes not a lifestyle convenience but a therapeutic tool. Consistent sleep timing, a cool and dark bedroom, and — where needed — discussion with the oncology team about pharmacological or psychological sleep support are all warranted.
Stress reduction and immune outcomes
Chronic psychological stress suppresses immune function — a finding robust across decades of psychoneuroimmunological research. For someone with cancer, where anti-tumour immune responses are partly responsible for treatment success, this is biologically significant.
A meta-analysis published in Psycho-oncology in 2019, synthesising data from 29 RCTs of mindfulness-based stress reduction (MBSR) and similar interventions in cancer patients, found that these programmes improved psychological distress, fatigue, and immune markers — specifically, patients who engaged in MBSR showed improved natural killer cell activity, the immune cells most directly involved in killing cancer cells.
A further RCT published in BMC Psychology in 2024 found that breast cancer patients receiving a 12-week mindfulness programme alongside chemotherapy had better quality of life, lower rates of chemotherapy-related cognitive impairment, and better treatment completion rates compared to usual care.
These studies don’t show that stress reduction cures cancer or replaces medical treatment. They do show that actively managing stress through evidence-based practices supports treatment tolerance and, through immune pathways, may support treatment efficacy.
What this means in practice
Exercise: Aim for as much structured movement as your energy and medical team permit. If intense exercise isn’t possible, even light activity — walking, gentle yoga, tai chi — shows benefits for fatigue, emotional wellbeing, and treatment tolerance. A cancer-informed exercise physiologist, where available, can design a programme that is safe during treatment and builds progressively.
Diet: Prioritise a Mediterranean-style whole-food pattern emphasising vegetables, fruits, whole grains, legumes, and healthy fats. Maintain adequate protein to support tissue repair. If appetite is compromised by treatment, an oncology-specialist nutritionist can help ensure adequate intake even when eating is difficult.
Sleep: Treat sleep as a treatment priority. Aim for seven to nine hours per night. If sleep is disrupted by treatment side effects or anxiety, raise this explicitly with your oncology team — it is a clinical matter, not an inconvenience to manage alone.
Stress management: Consider a structured practice — MBSR, cognitive behavioural therapy, or similar. Social connection, time in nature, and meaningful activity are also associated with better psychological and immune outcomes during treatment.
Supplements: Discuss any supplement use with your oncology team before starting. High-dose antioxidant supplements have not been shown to improve treatment outcomes and in some contexts may worsen them. Targeted supplementation addressing documented deficiencies — vitamin D, B vitamins, zinc, selenium — is more defensible and should still be reviewed with your team in the context of your treatment.
What the evidence does not yet show
The evidence is not yet sufficient to specify which combination of lifestyle interventions produces the greatest benefit, or which cancer types are most responsive. The CHALLENGE and LEAN trials are milestones, but they tested specific populations and specific interventions. Generalising their findings requires care.
There is also a real risk of this evidence being used to place burden or blame on people undergoing treatment — the implication that outcomes depend on how well you manage your lifestyle is not only stressful but reductive. Cancer biology is complex, treatment is often gruelling, and not everyone has equal access to exercise physiology, nutritional support, or psychological care. The evidence here supports the case for those resources being integrated into standard oncology care — not the case for individual patients holding themselves responsible for outcomes they cannot fully control.
The bottom line
The evidence that lifestyle factors influence cancer treatment outcomes is no longer preliminary. The CHALLENGE and LEAN trials represent a shift in the evidence base: structured exercise, undertaken during and after cancer treatment, improves disease-free and overall survival in a way that is clinically meaningful. Diet, sleep, and stress management add further support through distinct but complementary mechanisms.
None of this replaces surgery, chemotherapy, immunotherapy, or radiotherapy. But the data suggest that these interventions work better — and that patients tolerate them better and survive longer — when combined with the kinds of lifestyle support that have, until recently, been treated as peripheral. That framing is changing, and rightly so.
Scientific references
- Courneya KS, et al. Exercise and colon cancer survival: the CHALLENGE trial. New England Journal of Medicine. 2025. DOI: 10.1056/NEJMoa2502760
- Sanft T, et al. Exercise and dietary intervention during neoadjuvant chemotherapy for breast cancer: the LEAN randomised trial. Journal of Clinical Oncology. 2023. DOI: 10.1200/JCO.23.00871
- Bower JE, et al. Mindfulness meditation for younger breast cancer survivors: a randomised controlled trial. BMC Psychology. 2024. PMID: 39487509.
- Patel AV, et al. American Cancer Society guideline for diet and physical activity for cancer prevention. CA: A Cancer Journal for Clinicians. 2020;70(4):245–271. DOI: 10.3322/caac.21591
- Playdon MC, et al. Pre-diagnosis diet quality and survival in a nationally representative prospective cohort of patients with cancer. Cancer Epidemiology, Biomarkers & Prevention. 2022. DOI: 10.1158/1055-9965.EPI-21-0731
- Mustian KM, et al. Comparison of pharmaceutical, psychological, and exercise treatments for cancer-related fatigue: a meta-analysis. JAMA Oncology. 2017;3(7):961–968. DOI: 10.1001/jamaoncol.2016.6914
- Buffart LM, et al. Physical and psychosocial benefits of yoga in cancer patients and survivors: a systematic review and meta-analysis. BMC Cancer. 2012;12:559. DOI: 10.1186/1471-2407-12-559
This article is written for educational and informational purposes only. It is not intended as medical advice and should not be used to diagnose, treat, prevent, or cure any medical condition, including cancer. If you have a cancer diagnosis or are undergoing treatment, please discuss any lifestyle or dietary changes with your oncologist or medical team before making them. The studies cited reflect current research at the time of writing; the field is evolving rapidly and findings may be updated or superseded. Chloe Archard is a nutritional health coach, not a medical doctor.
