Nutrition for dogs and cats with cancer: What really matters in clinical practice?
- Ecommercy
- 2026-09-22
- 11:49
- 0 comments
Nutrition for oncology patients is an area surrounded by many oversimplifications. “Cancer feeds on sugar”, “carbohydrates must be eliminated”, “the diet should be high in fat”, “as many antioxidants as possible should be added” – pet owners frequently encounter recommendations like these.
In clinical practice, however, rather than searching for a single “anti-cancer diet”, it is far more important to provide appropriate nutrition for the individual patient, tailored to their nutritional status, type of treatment, concurrent diseases, gastrointestinal tolerance and ability to eat.
This article is based on the webinar “Nutrition for dogs and cats with cancer: What do we really know and how can we apply it in practice?”, presented by Angelika Gałkiewicz, Veterinary Technician and qualified Animal Nutritionist, who specialises in the nutrition of dogs and cats, including patients with chronic diseases.
The full webinar recording is included in the article. The text below provides an overview of the key topics discussed during the session, while the recording offers a more detailed explanation.
Full webinar recording:
There is no single diet for every oncology patient
This is one of the most important conclusions from the webinar.
A cancer diagnosis does not automatically mean that an animal’s entire diet needs to be changed. If a dog or cat maintains a healthy body weight and muscle mass, has a good appetite, normal bowel movements, does not vomit and tolerates their current complete diet well, changing the diet solely because of an oncology diagnosis may not always be justified.
A nutritional plan should take the whole patient into account, not just the type of cancer. Gastrointestinal health, kidney, liver and pancreatic function, current treatment, appetite, BCS and MCS, as well as concurrent diseases, all need to be considered.
In practice, this is far more important than trying to fit every patient into a single dietary approach labelled as a “cancer diet”.
Can cancer really be “starved” by eliminating carbohydrates?
One of the most common myths is that because cancer cells use glucose, carbohydrates should be restricted as much as possible.
This belief is based, among other things, on the Warburg effect. Many cancer cells do indeed show increased glucose metabolism. However, removing potatoes, rice or other carbohydrate sources from the diet does not deprive a tumour of its ability to obtain energy.
Cancer metabolism is flexible. Cancer cells can also use other substrates, including glutamine and fatty acids. At the same time, the host’s body can produce glucose through gluconeogenesis.
Studies in dogs with lymphoma also do not allow us to conclude that a low-carbohydrate diet improves prognosis. One classic study involving dogs with lymphoma evaluated a higher-fat diet supplemented with omega-3 fatty acids and arginine. Beneficial effects were observed, but because several dietary factors were modified simultaneously, the results cannot be attributed solely to carbohydrate restriction.
There is therefore currently no basis for routinely eliminating all carbohydrates from a dog’s or cat’s diet simply because cancer has been diagnosed.
When carbohydrates are included, well-tolerated sources of complex carbohydrates are generally preferred. However, the primary consideration should always be whether the diet meets the nutritional needs of the individual patient.
Anorexia and cachexia are not the same thing
One of the greatest nutritional challenges in oncology patients is reduced food intake.
Anorexia refers to reduced or absent food intake. It may be caused by the tumour itself, pain, swallowing difficulties, nausea, vomiting, mucositis or adverse effects of treatment.
Chemotherapy can also affect smell and taste. Patients may experience ageusia or dysgeusia, meaning that food they previously enjoyed may suddenly become unacceptable.
Cancer cachexia, however, is more than simply the consequence of inadequate food intake. It is a metabolic syndrome associated, among other factors, with chronic inflammation and the activity of pro-inflammatory cytokines. As a result, a patient may lose muscle tissue even while continuing to eat.
For this reason, with an oncology patient it is not enough to ask: How much do they weigh?
We also need to ask: What are they losing?
BCS is not enough. MCS should also be assessed routinely
Body Condition Score primarily evaluates body fat stores. It does not provide sufficient information about muscle condition.
A dog with a BCS of 7/9 may still have excess body fat while simultaneously experiencing significant muscle loss. This is why Muscle Condition Score becomes particularly important in oncology patients.
A comprehensive nutritional assessment should include body weight, BCS, MCS, a detailed nutritional history, clinical examination and laboratory results.
In cats, the speed of intervention is also important. Studies discussed during the webinar indicated that feline patients may be particularly vulnerable to malnutrition and muscle loss. Therefore, even a relatively small reduction in appetite or body weight should attract the attention of the veterinary team.
Do not change everything at once after diagnosis
A cancer diagnosis is an enormous emotional burden for the owner. A natural response is often the desire to do everything that might potentially help.
Within just a few days, the food may be changed, carbohydrates eliminated, fat increased, and oils, vitamins, mushrooms, plant extracts and various nutraceuticals introduced.
The problem arises when treatment begins at the same time.
If diarrhoea, vomiting or loss of appetite occurs a few days later, it becomes difficult to determine whether the cause is the disease itself, medication, the new diet or one of several newly introduced supplements.
Therefore, if the existing diet is well tolerated, changing it at exactly the same time as chemotherapy or another treatment begins may not always be advisable. If dietary changes are necessary, introducing them one at a time is generally a safer approach.
Home-prepared diets must be properly balanced
An individually formulated home-prepared diet can be a very good option for an oncology patient, but only if it meets the animal’s nutritional requirements.
Meat with rice or meat with vegetables alone does not constitute a complete and balanced diet.
An unbalanced diet may lead to deficiencies in calcium, zinc, copper, iron, iodine, vitamins or essential fatty acids.
An oncology patient does not need an additional metabolic problem caused by nutritional deficiencies. Particularly during intensive treatment, meeting the patient’s nutritional requirements should be one of the fundamental goals of nutritional management.
Energy requirements: calculate them, but above all monitor the patient
Calculated energy requirements are a starting point rather than a fixed value that should be followed regardless of changes in the patient’s condition.
If an animal loses weight despite receiving the calculated amount of energy, the feeding plan should be reassessed. Likewise, if the patient begins gaining excessive weight, the amount should be adjusted.
It is also important to establish how much the patient is actually eating.
An owner saying that “the cat keeps going to the bowl” does not tell us whether the cat is consuming 100%, 70% or only 30% of its nutritional requirements.
Monitoring actual energy intake is particularly important in hospitalised animals and patients with reduced appetite.
In severely malnourished patients, the risk of refeeding syndrome must also be considered. Introducing the full nutritional requirement too rapidly after a period of significant malnutrition can result in serious metabolic and electrolyte disturbances. Feeding these patients requires a gradual approach and appropriate monitoring.
Protein should primarily help preserve muscle mass
Cancer itself is not an indication for routine protein restriction.
One of the fundamental goals of nutritional management is to preserve muscle mass. Therefore, patients without contraindications should receive an adequate amount of high-quality protein.
This does not mean that “more is always better”. If the patient also has kidney disease, certain liver diseases or another condition requiring modification of protein intake, the nutritional plan needs to balance these different clinical requirements.
Interesting findings come from a study by Heinze et al. involving dogs with cancer undergoing chemotherapy. The test diet contained more protein and fibre and was supplemented with omega-3 fatty acids and antioxidants. Dogs receiving this diet showed improvements in a greater number of assessed quality-of-life parameters compared with the control group [4].
The study does not, of course, demonstrate that increasing protein alone has an anti-cancer effect. It does, however, illustrate why nutrition that supports overall condition and quality of life should be an important part of patient care.
Fat is a nutritional tool, not a way to “kill cancer”
Fat has a high energy density. This makes it possible to provide a substantial amount of energy in a relatively small volume of food, which can be useful in animals with reduced appetite.
However, this does not mean that every oncology patient should receive a high-fat or ketogenic diet.
Fat tolerance depends on the patient’s overall clinical condition. Particular caution may be required in some patients with gastrointestinal, pancreatic or liver disease, as well as when treatment itself affects food tolerance.
Again, the key principle is simple: the diet should be tailored to the patient, not to a dietary theory.
Omega-3 fatty acids may provide support, but they do not “treat cancer”
EPA and DHA are an interesting component of nutritional management, partly because of their role in regulating inflammatory processes.
However, they should not be presented to owners as substances that destroy cancer cells.
There is also no single universal “oncology dose” suitable for every dog or cat. The amount should be adjusted according to the overall diet, clinical condition, other supplements and ongoing treatment.
When selecting a source of omega-3 fatty acids, it is also important to remember that conversion of plant-derived ALA into EPA and DHA is limited, particularly in cats.
When a patient stops eating, do not wait for severe malnutrition
Loss of appetite should prompt intervention early.
However, the first step should not be to offer the patient a dozen different foods. The underlying reason for not eating should first be identified.
Is the animal nauseous? Is there pain? Is mucositis present? Are there adverse effects from medication? Has the perception of taste or smell changed?
This is particularly important in cats, which can develop food aversion relatively easily. If an animal eats a new food and subsequently feels unwell, it may refuse that flavour, smell or texture for a long time afterwards.
If, despite antiemetic treatment, pain management and other supportive measures, the patient still cannot meet their nutritional requirements, assisted feeding should be considered early enough.
If the gastrointestinal tract is functional, enteral nutrition is preferred
When a patient cannot independently meet their nutritional requirements but the gastrointestinal tract remains functional, enteral nutrition is generally preferred [5].
Depending on the patient’s clinical condition and the anticipated duration of nutritional support, options may include nasogastric or oesophagostomy feeding tubes.
An oesophagostomy tube does not prevent a patient from eating and drinking independently. It can therefore provide nutritional security during periods of reduced appetite while still allowing a gradual return to voluntary food intake.
Appropriate energy density is also important. Excessive dilution of food increases its volume and can make it more difficult to provide enough food to meet the patient’s requirements.
Supplementation: less is often more
Oncology patients are particularly likely to receive multiple supplements at the same time.
Vitamins, antioxidants, CBD, medicinal mushrooms, amino acids, herbal blends and other nutraceuticals may all be introduced without the attending veterinarian’s knowledge.
This is a mistake.
Every supplement should have a defined purpose, a known composition and an assessable safety profile. Potential interactions with medications are particularly important.
CBD is a good example. Because it can affect enzymes involved in drug metabolism, it may potentially alter the pharmacokinetics of other substances. The veterinarian should therefore always be informed if it is being used [3].
“Natural” does not automatically mean “safe”. If the composition of a product is unknown, its potential risks cannot be properly assessed.
Antioxidants during treatment require particular caution
High-dose antioxidant supplementation is another area that should not be approached automatically.
Some anti-cancer therapies involve mechanisms associated with oxidative stress. For this reason, intensive antioxidant supplementation during certain treatments, particularly radiotherapy, should always be discussed with the attending veterinarian.
This does not mean eliminating physiological amounts of vitamins and antioxidants present in a properly balanced diet. The concern relates primarily to additional high-dose supplementation.
What about raw diets?
In oncology patients undergoing treatment, particularly during periods of immunosuppression, the microbiological safety of food becomes especially important.
If a well-tolerated, balanced, heat-treated diet can be used, it will generally be a safer option than a raw diet.
However, the individual patient’s circumstances should not be ignored. In a cat that consistently refuses all other forms of food, an individual risk-benefit assessment may be necessary.
In clinical nutrition, sometimes the most important thing is simply ensuring that the patient eats.
The whole patient remains the priority
Nutrition in cancer should not be reduced to fighting a single dietary component.
Cancer cannot simply be “starved” by eliminating carbohydrates. Nor is there one supplement or one nutritional strategy that will be appropriate for every patient.
What matters far more is regular monitoring of body weight and muscle mass, meeting energy requirements, providing adequate high-quality protein, maintaining good gastrointestinal tolerance and intervening early when food intake begins to decline.
Nutrition should support both the patient and the treatment being provided.
That is precisely why we should not formulate a diet solely around the name of the cancer. We formulate it for the individual dog or cat.
About the webinar speaker
Angelika Gałkiewicz, Veterinary Technician, is a qualified Animal Nutritionist and Veterinary Technician specialising in individual nutrition plans for both healthy and ill dogs and cats. She is a member of the European Society of Comparative Gastroenterology and the European College of Veterinary and Comparative Nutrition. Her work combines a clinical approach with practical nutritional strategies tailored to the individual patient.
A full discussion of the topics covered in this article is available in the accompanying webinar “Nutrition for dogs and cats with cancer: What do we really know and how can we apply it in practice?”
References:
- Vail D.M., Thamm D.H., Liptak J.M., eds. Withrow and MacEwen's Small Animal Clinical Oncology. 6th ed. Elsevier, 2019.
- Fascetti A.J., Delaney S.J., eds. Applied Veterinary Clinical Nutrition. Wiley-Blackwell, 2012.
- Brown J.D., Winterstein A.G. Potential Adverse Drug Events and Drug–Drug Interactions with Medical and Consumer Cannabidiol (CBD) Use. Journal of Clinical Medicine. 2019;8(7):989. doi:10.3390/jcm8070989.
- Heinze C.R., Burgess K.E., Barber L.G. et al. Effects of a high-protein, increased-fibre, dry diet supplemented with omega-3 fatty acids on quality of life in dogs undergoing chemotherapy. Veterinary and Comparative Oncology. 2024;22(1):2–11. doi:10.1111/vco.12940.
- Marks S.L. Nutritional Management of the Hospitalized and Critically Ill Patient. World Small Animal Veterinary Association World Congress Proceedings, 2013.