Nutrition Before Cancer Treatment Starts: A Dietitian's Guide to Prehabilitation

Cancer is now something almost every family in the UK will face. Around one in two people born in the UK will be diagnosed with cancer at some point in their lives, and over 400,000 new diagnoses are now made across the UK each year — a record high. If you or someone you love has just received a diagnosis, you are not alone, and there is a lot you can do nutritionally in the days and weeks before treatment begins that genuinely makes a difference.

This period — after diagnosis but before chemotherapy, radiotherapy or surgery starts — is when dietitians talk about "prehabilitation." It is one of the most overlooked windows in cancer care, and one of the most powerful.

Why nutrition before treatment matters so much

It's tempting to assume the "real" work of getting through cancer starts once treatment begins. In nutritional terms, the opposite is often true.

Malnutrition is far more common at diagnosis than most people expect. Research assessing patients in the week before starting cancer therapy found that close to six in ten had either malnutrition or were already at risk of it, and being malnourished at the start of treatment was independently linked to poorer survival. Other studies estimate the prevalence of malnutrition in cancer more broadly at anywhere between a quarter and four in five patients, depending on tumour type and stage. In short: many people are already nutritionally compromised before their first cycle of chemotherapy or their operation date, often without realising it.

This matters because the body's ability to tolerate treatment, heal after surgery and maintain muscle mass through chemotherapy is heavily influenced by nutritional reserves going in. Multimodal "prehabilitation" programmes — which typically combine nutrition, structured exercise and psychological support in the weeks before treatment — have been associated with fewer post-operative complications, better preservation of muscle mass and physical function during chemotherapy, and improved patient adherence to nutritional advice overall.

Protein: the cornerstone of prehabilitation

If there's one nutritional priority in the run-up to cancer treatment, it's protein.

Cancer and its treatments increase protein requirements — in some cases up to double the intake recommended for a healthy adult — because the body needs extra protein to preserve muscle mass, support immune function and repair tissue. Clinical prehabilitation programmes for colorectal and oesophageal cancer surgery generally aim for at least 1.2–1.5g of protein per kilogram of body weight per day (roughly double a standard healthy-adult intake), often supported by two protein-rich meals a day of 25g or more, plus a protein source before bed.

Practical ways to build this in before treatment starts:

• Include a protein source at every meal and snack — eggs, fish, poultry, dairy, tofu, beans, pulses, or a protein shake if appetite is limited

• Aim for a protein-containing snack before bed, such as Greek yoghurt or a small protein drink — research in prehabilitation programmes shows this evening protein boost is often where people see the biggest gains

• Don't wait for weight loss to appear before acting — muscle loss can begin before the scales move

Anti-Inflammatory Reset Meal Plan

Buy Now

Building your nutritional reserves, not just "eating healthily"

General "healthy eating" advice (more vegetables, less processed food) is a good long-term goal, but it isn't quite right for the prehabilitation window. The priority here is building reserves of energy, protein and micronutrients — even if that temporarily means prioritising more energy-dense foods than you'd normally choose.

Useful principles for the weeks before treatment:

• Don't restrict. This is not the time for calorie-controlled or weight-loss diets, even if you'd usually be trying to lose weight

• Little and often can be easier to manage than three large meals, especially if diagnosis-related anxiety is affecting appetite

• Iron, vitamin D and B12 status is worth checking with your GP or dietitian, particularly if you have symptoms like fatigue, as deficiencies here can affect how you cope with treatment

• Address any existing digestive symptoms (reflux, bowel changes, appetite loss) now — sorting these out before treatment starts means one less thing working against you once side effects begin

What the evidence says about outcomes

Studies of nutritional prehabilitation before major cancer surgery have shown it can meaningfully increase daily protein intake — from roughly 1.2g/kg to over 1.6g/kg of body weight in structured programmes — and this has been linked to better preservation of physical fitness and function going into surgery. Evidence is still developing on how directly this translates into shorter hospital stays, but the direction of travel across the research is consistently positive: patients who go into treatment better nourished tend to cope with it better.

This is also why nutritional screening at diagnosis is increasingly recommended as standard practice — but in reality, provision varies hugely across the NHS, and not everyone is offered a dietitian referral before treatment starts. If you haven't been offered nutritional input and treatment is approaching, it's worth asking your oncology team directly, or seeking a private consultation with a dietitian experienced in oncology nutrition.

A note on "boosting your immune system" and restrictive diets

Understandably, a new diagnosis often triggers a search for the "one thing" that will help — and this is where a lot of misinformation lives online. There is no single food, juice, or extreme diet proven to "starve" cancer or boost immunity in a way that improves outcomes, and restrictive approaches (fasting, very low-carbohydrate diets, cutting out entire food groups) can actively work against you by reducing the energy and protein reserves you need most right now. If you're considering a specific dietary approach you've read about, it's worth checking it against evidence-based sources — the British Dietetic Association and World Cancer Research Fund both publish reliable, myth-busting guidance for people living with a cancer diagnosis.

Getting personalised support

Every cancer diagnosis, treatment plan and starting nutritional status is different, which is exactly why generic advice can only take you so far. A personalised prehabilitation nutrition plan — built around your specific treatment pathway, current intake and any existing health conditions — is one of the most practical things you can put in place in the early weeks after diagnosis.

If you'd like tailored support, I offer 1:1 oncology nutrition consultations to help you build a realistic, evidence-based eating plan before treatment starts. Book a consultation or explore my meal plans designed to make protein-rich, treatment-ready eating simple.

This article is intended for general information and does not replace individual medical or dietetic advice. Always speak to your oncology team, GP or a registered dietitian before making significant dietary changes around cancer treatment.

Sources: Cancer Research UK, Cancer in the UK Report 2026; World Cancer Research Fund, UK Cancer Statistics (2026); British Dietetic Association, oncology nutrition resources; ScienceDirect, prevalence and prognostic impact of malnutrition at cancer diagnosis (2026); Journal of Health, Population and Nutrition, systematic review on severe malnutrition prevalence in cancer (2025); Advances in Nutrition, prehabilitation and nutritional optimisation review (2025); NCBI/PMC, adherence to nutritional intervention in multimodal prehabilitation (Fit4Surgery study).