Pet Cancer Options

Evidence-Based Treatment Guide

Supportive care

Nutrition During
Cancer Treatment

What your pet eats during cancer treatment can influence their energy levels, immune function, body condition, and ability to tolerate chemotherapy or other interventions. Nutritional support is a meaningful part of the overall care plan — not an afterthought.

The right approach depends on your pet's specific diagnosis, treatment protocol, body condition score, and any concurrent health conditions. For individualised dietary planning, the most qualified person to consult is a board-certified veterinary nutritionist (DipACVN). Ask your veterinary oncologist or primary vet for a referral.

The information on this page is drawn from peer-reviewed veterinary literature. It is educational only and does not replace professional veterinary nutritional advice.

Key concept

Cancer Cachexia

Cancer cachexia is a metabolic syndrome characterised by involuntary loss of skeletal muscle mass — and often fat — that cannot be fully reversed by simply increasing calorie intake. It is driven by tumour-related metabolic disturbances, including altered carbohydrate, protein, and lipid metabolism, as well as systemic inflammation mediated by cytokines such as TNF-α and interleukins.

A pet may develop cachexia even if their appetite appears normal and they are eating adequate food. This distinguishes it from simple starvation, where weight loss responds directly to increased nutrition.

What to watch for

Look for muscle wasting over the spine, hindquarters, and temporal muscles of the head — these areas lose mass early. Your vet can assess this using a Muscle Condition Score (MCS), separate from body weight or body condition score. Weight loss alone can underestimate the degree of muscle loss, particularly in patients who are overweight.

Preserving lean muscle mass and maintaining an appropriate body condition during treatment is clinically meaningful. Patients with better nutritional status at the start of treatment tend to experience fewer dose-limiting complications and may tolerate therapy better. Early nutritional intervention — before significant muscle loss occurs — is therefore preferable to trying to reverse cachexia once it is established.

Macronutrients

Protein During Treatment

Cancer cachexia preferentially catabolises skeletal muscle protein. Maintaining adequate intake of high-quality, highly digestible protein is therefore an important component of nutritional support during treatment — not to build mass, but to help slow the rate of muscle loss.

Animal-sourced proteins — such as chicken, fish, eggs, and lean meat — generally offer high biological value and a complete essential amino acid profile, and are well utilised by both dogs and cats. Commercial diets formulated for cancer patients or recovery often prioritise protein digestibility for this reason.

Important caveat

Protein requirements vary considerably between individual patients. Some conditions — including concurrent kidney disease, hepatic dysfunction, or specific tumour types — may require modified protein levels. Do not significantly increase protein intake, add protein supplements, or switch protein sources without discussing it with your veterinary team. The goal is the right amount of the right protein for your pet.

Evidence-reviewed

Omega-3 Fatty Acids (EPA & DHA)

The long-chain omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have well-characterised anti-inflammatory properties. In the context of cancer, this is relevant because tumour-driven inflammation contributes to cachexia and may affect treatment tolerance.

Published evidence

Research by Ogilvie and colleagues at Colorado State University — including a prospective study published in Cancer (2000) examining dogs with lymphoma receiving doxorubicin-based chemotherapy — found that dietary supplementation with fish oil and arginine was associated with improved disease-free interval and overall survival time compared to a control diet. This represents meaningful evidence within veterinary oncology, though it should be noted that the study population was dogs with a specific tumour type, and findings cannot be automatically extrapolated to all cancers or to cats.

Fish oil (marine-sourced) is the most direct dietary source of EPA and DHA for dogs and cats. Plant-derived omega-3 sources such as flaxseed oil provide alpha-linolenic acid (ALA), which is only poorly converted to EPA and DHA in companion animals and is not a practical substitute.

Before you supplement

Discuss dosing with your vet before adding fish oil. Excessive supplementation can cause gastrointestinal upset, and high doses may affect platelet function — a consideration for patients undergoing surgery or with thrombocytopenia from chemotherapy. The appropriate dose depends on your pet's weight, diet, and clinical status.

Safety warning

Raw Diets Are Contraindicated During Chemotherapy

Do not feed raw meat, raw eggs, or unpasteurised dairy to a pet receiving chemotherapy. This applies even if your pet was eating a raw diet before their cancer diagnosis.

Chemotherapy causes immunosuppression — most significantly neutropenia (a reduction in circulating neutrophils, the white blood cells that defend against bacterial infection). During neutropenic periods, the immune system cannot mount a normal response to bacterial pathogens.

Raw animal-sourced foods carry a meaningful risk of contamination with Salmonella, Listeria monocytogenes, Campylobacter, and other organisms. In an immunocompromised patient, exposure to these pathogens can cause serious — potentially fatal — systemic infection. Commercial raw diets, whether fresh or frozen, do not eliminate this risk.

The American Veterinary Medical Association (AVMA), the World Small Animal Veterinary Association (WSAVA), and veterinary oncology services routinely advise against raw diets for immunocompromised patients. If your pet's current diet contains raw components, speak to your oncologist before their first chemotherapy treatment about transitioning to a commercially prepared, heat-processed diet.

Proceed with caution

What Not to Change Without Veterinary Guidance

It is natural to want to do everything possible to help your pet, and nutrition is an area where many owners look for ways to take action. However, some well-intentioned changes can interfere with treatment or cause harm. The following should not be altered or added without discussion with your veterinary team:

Nutritional supplements

This includes vitamins C and E, antioxidant supplements, and selenium. Many chemotherapy drugs and radiation therapy work in part through oxidative mechanisms. High-dose antioxidant supplementation during treatment may theoretically blunt this effect — the clinical significance is debated, but it is a recognised concern. Do not add supplements without first checking with your oncologist.

Major diet changes during active treatment

Switching foods abruptly during chemotherapy can cause gastrointestinal upset — particularly diarrhoea and vomiting — which is already a common treatment side effect. If a diet change is indicated, your vet or nutritionist will advise on how to transition gradually and at a suitable time.

Herbal remedies and 'natural' treatments

Many herbal products have pharmacological activity. Some — including preparations containing St John's Wort — affect CYP450 enzymes involved in drug metabolism, with the potential to alter chemotherapy drug levels. Others have unknown interaction profiles. 'Natural' does not mean safe to use alongside cytotoxic drugs. Disclose all supplements and herbal products to your oncologist.

Ask your veterinarian for a referral to a board-certified veterinary nutritionist

A Diplomate of the American College of Veterinary Nutrition (DipACVN) can assess your pet's individual nutritional status, body composition, and treatment plan to create a diet strategy tailored to their needs. This is the evidence-based standard of care for cancer patients with complex nutritional requirements.

Nutrition During Cancer Treatment