Nutrition and Cancer: What We Can and Can’t Do

In case you were wondering what a typical day in the life of a Veterinary Nutrition Specialists is like, my working days are mostly filled by those with chronic diseases: diabetic cats with kidney disease; dogs with food allergies and pancreatitis; maybe a diabetic dog with food allergies, history of pancreatitis, kidney disease, AND a picky appetite just to make it interesting. But on one particular day a few years back my first appointment of the morning was a little different. The reason for the visit as listed in the medical chart was “questions about preventing cancer” and my soon-to-be patient was a 4 month old Golden Retriever puppy full of happy, healthy, fluffy, puppy cuteness.


Not an actual picture of my patient, but just as cute.

After introducing myself to the puppy and his people I quickly learned what brought them in seeking cancer prevention advice. Turned out that this particular puppy was the fourth in a series of GoldenS cared for by the owners over the previous 20+ years. The first died at 10 years of age from hemangiosarcoma (an aggressive cancer of blood vessels that usually starts in the spleen and quickly spreads in the body), the second at age 6 from osteosarcoma (an aggressive cancer of the bone that usually starts in one bone and can spread throughout the body), and the third died at 2 years of age from lymphoma (an aggressive cancer of one of the white blood cell families, that can go and do whatever it wants). Their most recent loss was less a year before our appointment, so needless to say, this couple was very concerned about losing this new puppy too soon. They wanted to know if there was anything they could do diet and supplement-wise to prevent cancer from striking another four-legged family member.



Another gratuitous puppy picture.

If any of my readers were wondering that same thing, the short answer was no. There are no proven dietary changes or nutritional supplements that have been definitively shown to prevent cancer in dogs and cats. Cancer is a leading cause of death in dogs and cats with genetics, viruses, environmental toxins, age, and neuter status all having a direct or indirect role in the development of certain types of cancer.

So what do dog and cat caregivers need to know about cancer and possible nutritional prevention/treatments?

#1: What causes cancer?

Cancer results from damage to DNA (the genetic code of every cell) that 1) allows that cell to replicate itself unchecked, 2) to avoid normal housekeeping systems that would otherwise destroy an abnormal cell, 3) to induce new blood vessels growth to supply the cancerous cells with nutrients, and 4) to spread either locally or distantly (or both).

Cancer incidences are higher in certain pure-bred dogs than in mixes; viruses such as feline leukemia virus (FeLV) and transmissible venereal tumors (TVT) can induce cancer development and are acquired by close contact with infected animals; unneutered male dogs can develop testicular tumors just as unneutered females can develop uterine cancer (the risk of these two tumor types is virtually eliminated with neutering); cats and dogs living in households with heavy smokers have an increased risk of oral and nasal cancers due to environmental tobacco exposure. Additionally dogs and cats today are living longer thanks to vaccines, complete and balanced commercial diets, and advances in medical prevention/treatment of other diseases. Essentially, by preventing other potentially fatal diseases we have opened up the playing field for cancer in older aged dogs and cats.

Breed predispositions play an especially important role in cancer occurrence in Golden Retrievers. Goldens are beautiful, smart, dedicated family dogs, steadfast companions, but they are also a breed that has among the highest risk for cancer development at any age. This is one of the primary reasons for the development of Golden Retriever Lifetime Study. This study enrolled 3000 young Goldens and will track the genetics, environment and diet of each individual dog to help identify risk factor and possible prevention strategies for cancer as well as other chronic disease. This is a huge undertaking not only by the researchers, but the family committing their beloved canines and their own time to this study. At the time of my puppy appointment, the Golden Retriever Lifetime Study had not yet been launched and it will be at least a decade, if not longer, before we have any inkling of results.

What can dog and cat caregivers do about these risks? If you are adopting a purebred dog or cat, learn about the breed and what conditions can typically affect that breed. Do your research on any potential breeders as well. Find out what steps (if any) they are taking to screen their breeding pairs for known and potential health problems. Is the breeder tracking disease incidences (including cancer occurrence) in their lines? Once that cat or kitten is in your care, vaccinate for FeLV, if they are considered to be at-risk for this disease. Since FeLV is a “social” virus that required direct contact with an infected cat, indoor only cats in a FeLV-free household don’t typically need annual boosters. But talk to your veterinarian about your individual cat’s risk before stopping any vaccine regime. Canine TVT is a sexually transmitted disease, and both testicular and uterine tumors require intact reproductive tracts so the best way to prevent all of these is by neutering your dog. And if you are a smoker who hasn’t/can’t/doesn’t want to end their habit, at least smoke outside away from your dog or cat.


Old age happens, but it’s better than the alternative.


#2: What about specific foods and cancer risk?

If you are reading my posts, you are interested in canine and feline nutrition and have likely read other websites that claim that “kibble causes cancer” or that there are “cancer causing preservatives in pet food”, but scientific evidence for these claims is very much lacking. These claims are also almost always made by either a distraught pet owner looking for someone to blame for unexpected cancer diagnosis or by a person or business trying to market their own special line of “miracle cure-alls.” Our old Labrador, Maggie, lived 14 ½ years eating primarily dry dog food (with the occasional pizza or bread roll stolen from the counter when we weren’t looking), and ultimately died from a stroke-like event that hit her one morning. My 18-year-old cat Oliver is asleep next to me right now, has eaten dry commercial food his whole life and, other than his arthritis, is the picture of geriatric health; while our 3-year-old cat Cosette had eaten a variety of canned and dry foods over her short life, loved eating cat grass (that I grew myself) every day, and just died from transitional cell carcinoma in her left kidney (a rare cancer in cats, let alone in one so young). I don’t blame Cosette’s once-a-day cat grass habit for her developing cancer nor do I attribute Oliver’s longevity and health to dry food; cancer happens even to good cats and dogs.

But what does the vet literature say? There are some published veterinary studies that have tried to find an association between specific food intakes and cancer risk. One study looked at feline oral squamous cell carcinoma and another looked at thyroid adenomas in cats, but both of these studies relied on owners to report frequency and types of foods given over years to decades prior to the cancer diagnosis. Another study in dogs tried to draw a connection between intake of fresh fruits and vegetables with lowered risk of transitional cell carcinoma in Scottish Terriers. Again, these researches relied on owners to recall types and amount of fresh produce fed over the previous years. Most people can’t recall how much fruit and veg they fed themselves over the last week, let along how much they fed their dogs. I’ve worked with people who can’t even remember the name of the food they use (“it’s the purple bag with black writing”) or live in household with multiple feeders (intentional and unintentional). Recall bias is essentially the over- or under-reporting of foods and lifestyle habits that a responder thinks may be associated with a particular disease state. Recall bias is a significant enough problem in human health studies that nutritional epidemiologists have almost completely abandoned this method of data collection, yet for some reason veterinary researchers still rely on it. Food recall is always faulty in my clients, and they are highly motivated to remember their dog or cats food intake. To date, any veterinary study using only caregiver food recall to draw conclusions about diet and cancer risk in dogs and cats should be taken with a heavy dose of skepticism.

What do cat and dog owners need to know about commercial diets and cancer risk: Improvements in disease prevention, nutritional needs, medical care, and diagnostics mean that today’s cats and dogs are living to ages when accumulated DNA damage can result in cancer. Feed a complete and balanced diet that meets your individual animal and family’s lifestyle needs. If you want to feed a varied diet or a portion of fresh foods on a regular basis, that is no problem, as long as the overall diet still meets your dog or cats nutritional needs, they tolerate it well, and the foods selected are not harmful (no toxic foods like garlic or grapes, and avoid feeding foods that contain Salmonella or Campylobacter).

vegetarian dog

The wild ‘carnivore’ back from the hunt.

 #3: What about the role of obesity in cancer development?

This may be the one area of nutrition and health that could impact disease prevalence. In people, obesity has been shown to increase risk of specific cancers, such as uterine, liver, and post-menopausal breast cancer. These same associations haven’t been seen in dogs or cats, but calorie restriction has been shown to decrease cancer risk in rodent and primate models. The only published prospective (meaning they started with healthy dogs and followed them forward in time) study in dogs to date that looked at lifetime intakes and disease prevalence showed an equal number of cancer occurrences in lean and overweight dogs, but the small sample size (only 48 dogs in total) make this comparison almost meaningless. The results of the Golden Retriever Lifetime Study may give us more insight into this question.


What do cat and dog owners need to know about obesity and cancer risk: Lack of scientific data doesn’t mean that there is not an association between obesity and cancer development in companion dogs and cats, it just means that we don’t have a study that could answer this question. Even in the absence of a clear link between obesity and cancer, excess weight is a proven risk factor for other problems in dogs, and cats including joint disease, diabetes, skin disease, breathing difficulties, and at least in dogs has been shown to decrease longevity.



There may be less to love, but you can love them longer.

#4: What about the role of carbohydrates and cancer?

A quick Google search on “carbohydrates and cancer” will give pages of websites claiming to prevent or cure cancer by avoiding carbohydrates, and especially carbohydrates that include GMOs and gluten (the “evil” ingredients du jour). And there is big money in making these kinds of diet claims. Just look at the recent Belle Gibson story. Her fake cancer and food cure story garnered her hundreds of thousands of followers (and dollars), spawned a book, an app, and stories in international magazines, until she was recently exposed as a fraud and a thief.

There is one veterinary study that the anti-carb people like to point to and shout, “See, carbohydrate influence cancer!” It was published in 2000 and looked at response to cancer treatment in dogs with lymphoma fed a low carbohydrate (18% of the calories) diet supplemented with fish oil and arginine. Low carb advocates (including one of the lead authors) have cherry-picked the results of this study to make claims like “dogs with cancer should be fed a low carbohydrate diet” and “carbohydrates feed cancer” (emphasis is mine), yet when you read the entirety of the paper you learn that the control diet (the non-supplemented diet used as a comparison for the supplemented diet) had the exact same carbohydrate content as the study diet, just no fish oil and extra arginine. And the low carb control diet had absolutely no influence on cancer progression relative to expected outcomes. Again, feeding a low carbohydrate diet alone made no difference in disease free interval or survival time in these dogs with lymphoma. Yes, cancer cells utilize blood sugar (glucose) more rapidly than the surrounding normal cells, but this happens whether the individual consumes carbohydrates directly in their diet or if the blood glucose is produced from glycogen (a type of carbohydrate stored in the muscle and liver) or from gluconeogenesis (production of glucose in the liver) from metabolism of fatty acids and amino acids (building blocks of protein). The body of an adult, non-reproducing, non-lactating animal is very good at maintaining blood sugar levels, even when fed a carb-free diet. Additionally, there is not a single veterinary study that has demonstrated that dogs or cats fed low to no carbohydrate diets have less cancer incidence than dog or cats fed moderate to high carbohydrate diets. Not that I am advocating that dogs and cats should be fed lots of starches and simple sugars, I just don’t want people to wave the cancer prevention/treatment flag when touting the “benefit” of a carbohydrate-free diet.


What do cat and dog owners need to know about carbohydrates and cancer risk: At this time there is no evidence that a diet with a low (less than 20% of the calories), moderate (20-40% of the calories), or high (greater than 40% of the calories) carbohydrate content has any bearing on cancer development in dogs and cats. There may be other reasons to feed a reduced carbohydrate diet, like management of feline diabetes, and animals with insulin secreting tumors (insulinomas) will often benefit from a reduction in overall carb intake, but like for all conditions the specific diet selected for your dog or cat should encompass their whole health needs.


Porkchop and corn

Psst, no one told her she wasn’t supposed to like corn.


#5: What about antioxidants for cancer protection?


The most common supplements marketed for “cancer prevention” or “cancer treatment” include combinations of antioxidant compounds, such as vitamin C, vitamin E, carotenoids, and selenium. On the surface this may seems to make sense. Antioxidants exist within each cell to balance and prevent the accumulation of reactive oxygen species (ROS) that are formed during normal cellular metabolism. These ROS can have damaging effects on nearby DNA, effects that could potentially end up in cancer development. The balance between formation of ROS and antioxidant capacity of the cell is dependant on dietary intake of antioxidants compounds, as well as the demand on the antioxidant systems through exposure to oxidative damage. So supplementing antioxidants seems like a smart thing, right? Maybe not. In people increased intake of antioxidants may influence cancer development, but not in the way we want. Prospective studies in people have shown that supplementing beta-carotene and vitamin A may increase the risk of lung cancer in smokers; high dosage vitamin E may increase prostate cancer risk; and women (but not men) taking high dosages of vitamins C and E, selenium and zinc, may actually be at an increased risk of skin cancers.  And there are a number of other studies looking at different cancer that have shown no effect (good or bad) of antioxidant supplementation. It is important to note that these studies in people were based on longer term (5-15 year studies) using tens of thousands of individuals. Veterinary medicine hasn’t done anything like this, until the Golden Retriever Lifetime Study and even that would be considered small by human study stanards.  There are no published studies evaluating specific antioxidant supplementation and cancer prevention in dogs and cats, though increased antioxidant intake in older dogs may help protect cognitive ability.

What do cat and dog owners need to know about antioxidants and cancer risk: There is no evidence that increased intake of antioxidants will prevent cancer in dogs and cats, and if anything, the studies in people have demonstrated that megadoses (10-100X normal dietary requirements) of certain antioxidants may actually increase risk of certain cancers. Antioxidants consumed as part of a healthy, balanced diet are fine, as are naturally occurring antioxidants found in fresh fruits and vegetables (non-toxic ones of course). There may also be some benefit to cognitive function with moderate increases in antioxidant intake in middle age to older dogs and cats.


food scale

It is all about finding the right balance (and avoiding known risks).

The bottom line…

There are no proven dietary strategies or techniques to prevent cancer development in dogs and cats. Defects in tumor suppressor genes, exposure to environmental toxins, obesity, and chronic inflammation have been proposed as causes of tumor development in people and many of these same mechanisms may occur in dogs and cats. Genetic factors and environmental toxins may not be avoidable or preventable, but avoiding obesity and feeding a complete and balanced (no deficiencies, no excesses) are within every caregiver’s control.




Happy Feeding!

Lisa P. Weeth, DVM, MRCVS, DACVN



13 thoughts on “Nutrition and Cancer: What We Can and Can’t Do

  1. Call me crazy but with cancer being a leading cause of death, shouldn’t we be doing more research with nutrition and cancer? I can see why those clients asked you about how they could prevent cancer in their puppy, our Western medicine focuses mainly on treatment not prevention.

    Honestly, with my 17 (yes!) year old dog currently fighting mast cell tumors with chemo, I’m hungry (pun intended) for nutritional support for my dog.


    • I agree Julie. Personally I like to focus on prevention of disease whenever possible. With cancer though, there are so many variable that can trigger disease, and they likely overlap and have a cumulative effects, so it has been hard to ferret out the specifics after the fact. What we need is more studies like the Purina Lifespan Study (followed 48 related Labradors) and the Morris Animal Foundation Golden Lifetime Study (following 3000 mostly unrelated Goldens), which is following animals over the course of their natural lifespans and collecting diet and medical details along the way. It is likely many different factors that come into play, but hopefully the Golden Lifetime Study will help us identify a few of those. We know that genetics play a big roll in certain canine cancers (Mast Cell Tumors make me think you may have a pug or a Boston, for example) and while there is nothing that we know of (yet) that will prevent high risk breeds from developing MCT, it is one of the cancers that I tend to manage with dietary changes. There are certain foods that are known to trigger mast cell degranulation in people and I try to avoid these in my patients whenever possible. A fairly good list can be found at The BIG caveat is we don’t know whether the foods on this and similar lists are definite MC triggers in dogs, but since dogs don’t require ingredients, only nutrients, it won’t hurt to avoid these foods. Best wishes to you and your pup!


    • Hi Jill,

      Thank you for reading and posting this comment and I apologize for my late reply. I don’t think we have a straight forward answer yet as to whether early neutering (spay or castration) definitely promotes cancer development in dogs, but a study published in 2013 looking at Golden Retrievers seen at UC Davis in California ( definitely indicated that this may be true.

      This group looked at Goldens that presented to the referral hospital between 2000-2009 and divided dogs into 3 categories: intact, early neuter and late neuter. They found an increased occurrence of lymphoma in the early neuter group of both males and females and an increased occurrence of both hemangiosarcoma and mast cell tumors in the late neuter group. I think these results are intriguing, but when I read the full article there were a few things that made me question whether these finding can be extrapolated to the overall dog population.

      (1) The first being that they only looked at Goldens, a breed with a genetic predisposition to cancer development. So we don’t yet know if these finding can be applied to other breeds or even other cancers.

      (2) The researchers’ definition of “early” and “late” were a bit different than other neuter studies I’ve read. They selected 12 months as the cut off between early and late without any explanation that I find in the paper. Skeletal development slows and growth plates close at around 12 months (give or take a few weeks to months depending on the breed and what bone you are looking at) and even if growth plates are open past 12 months of age very little longitudinal (upward) growth continues past this time point so from a joint disease standpoint, which was their other disease group of interest, 12 months seems rather late in the game to me. Many shelters are neutering dogs and cat before 6 months of age to prevent sexual maturity and help with pet overpopulation and it would have been interesting if they looked at the effects of neutering before 6 months.

      And (3) these dogs were seen by a referral teaching hospital that has an entire building dedicated to cancer diagnosis and treatment (the Comparative Cancer Center). I wonder whether they saw a representative sample of California Goldens, or if the presence of the CCC served as a draw for oncology patients and may have skewed their results. To put it another way, do neutered dogs truly get these three cancers more often than intact dogs or does the presence of the referral center bring a disproportionate number of cancer patients through their doors.

      Two things that I am looking forward to that may help answer this and other questions are the Golden Lifetime Study ( ) and the Canine Disease Mapping Project ( These next 10-15 years are going to be exciting times!



  2. Dear Dr. Weeth , I liked very much your article but I`m still confused about the role of carbs in cancer.
    My vet removed about 5 or 6 moles from my dogs abdomen and they were skin melanoma in it’ s initial stages. An chest x ray and an ultrasound of the abdomen came clean so the cancer has not spread . My vet said no further treatment.

    So , does he still has cancer ?

    I want to know if I have to change his diet,

    I currently feed him a homemade diet the nutricionist gave me , of turkey , mackerel, 120 gms. of
    brown rice and green beans , carrots, pumpkin , asparagus and zucchini , with fish oil and coconut oil, besides the supplements to balance the diet.

    It has 83 gms. of carbs (49 %) mostly because I give him considerable amounts of these vegetables because he is acustomed to eat a lot.

    Does this diet counts as a low carb diet ? or I have only to count the simple carbohydrates ?
    should I stop giving him dog cookies ?

    Thanks a lot !!


    • Hi Luis,

      Thank you for reading and I apologize for not seeing and replying to your question sooner. I’m sorry to hear that your dog went through a cancer diagnosis and treatment, but it sounds like your dog had an early stage and that your vet was able to get it all. It sounds like you caught it quickly (great job!) and surgery was curative for your pup (yeah!). All good news.

      The relationship between carbohydrates and cancer is a much debated topic. Many holistic vets and natural food advocates will claim that carbs in general, and the refined cereal grains in commercial pet foods in particular, will promote cancer development, but the science doesn’t support this. Genetics and age play a much bigger roll. Most of the arguments around dietary carbohydrates center on blood sugar levels, but unless the dog or cat is diabetic, their blood sugar is going to be tightly regulated. Even studies in dogs undergoing cancer treatment have shown that ultra-low carb diets have no effect on progression or prognosis of the cancer.

      Based on the information you gave me, I would consider your dog’s current diet to be more moderate carbohydrate rather than low or high. But that’s ok. The ingredients and level of carbohydrates look absolutely fine and if anything the amount of fiber and phytonutrients (especially antioxidants) in the grains, fruits and vegetables he is eating may have a protective effect. And I’d keep the cookies. Life is always better with cookies. 🙂



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  4. Hi Lisa, what a nice article!
    I’m a vet focused in nutrition and have found your article very informative and well supported.
    I’m also looking forward to seeing what insights the Golden Retriever study can provide us.
    I wanted to asked you about the relation between obesity and inflammation.
    I’m surprised about the paper you have shared by Freeman et al where they didn’t find differences in terms of cancer prevalences when comparing dogs according to theur BMI.
    What are your thoughts about the approach to prevent chronic inflamamation (which is sort of like a spark for some cancers) by preventing overweight/obesity?
    Thanks a lot.
    I’ll try to keep all your blog stuff.
    It’s very good. Congrats!
    I’m surprised fo


    • Hi Jose,

      Thanks for reading and taking the time to write a comment, and I’m glad you enjoyed the post! I, too, am looking forward to the Golden Retriever study and what it may tell us about lifestyle and disease risk in that breed. The relationship between obesity, chronic inflammation and cancer is an interesting one. In people we know that obese individuals are at an increased risk of certain cancers, like post-menopausal breast cancer in women and esophageal/gastrointestinal and liver cancers in men and women, but these are cancer types that we don’t see very often in companion dogs. I am not an Oncologist so this is just my outsiders opinion on this but I suspect the reason we don’t see (or at least can’t prove) the same types of cancer prevalence in obese male and female dogs are at least two-fold.

      1) The types of cancers dogs get appear to have different prevalences than the cancers that people more commonly get. For example, lymphoma, osteosarcoma and hemangiosarcoma are 3 of the more common canine cancers and in people there does not appear to be a relationship between obesity and development of these cancers. So maybe obesity in dogs does not have an impact on the types of cancers dogs get more often.

      2) Monitoring and tracking of cancer incidence is different in dogs vs people. Meaning that most people diagnosed with cancer will seek medical treatment and definitive diagnosis, whether their cancer is “treatable” or not, and those diagnostic codes get recorded and often get entered into larger databases looking at disease prevalence among populations. The sample sizes in human cancer epidemiology studies number in the hundreds of thousands. Compare that to veterinary medicine where it is up to the individual owners to seek treatment and a diagnosis. If/when a definitive cancer diagnosis is found unless that animal is seen at one of the larger teaching hospitals or corporate referral practices, those diagnoses will languish in a medical record and not used for further study. Even in university settings the sample sizes in veterinary cancer epidemiology studies for individuals cancer types often number less than one hundred. Not hundreds of thousands or even tens of hundreds. Less than one hundred. Raghaven et al 2005 study looking at the relationship between vegetable consumption and TCC in Scotties has 92 cases of TCC between Jan 1, 1995, and Aug 1, 2003. Olgilvie et al’s 2000 paper looking at the diet modifications in dogs with high-grade lymphoma enrolled 32 dogs (time frame for enrollment was not reported). One of the “larger” studies looking at diet influences on survival times in dogs with mammary carcinoma by Shofer et al in 1989 include 145 dogs. None of these studies really looked at or even objectively measured obesity in these dogs. I tried to do that in my study ( of dogs at UC Davis but it was really hard to evaluate with so many different cancer types and small sample sized in each group. So maybe obese dogs do have an increased risk for mammary cancers (in females) and esophageal/gastrointestinal and liver cancers (in males and females) but we as veterinarians are not recording these finding (for whatever reasons) and if they are recorded they aren’t being used for larger scale studies.

      I think it avoiding obesity is dogs (and cats) good for for everyone. Even without the concern that excess fat tissue is secreting hormones and adipokines that promote a chronic inflammatory states, mechanical stress on joints, cardiovascular, and respiratory systems is reason enough to avoid.



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