Feeding the Dog with Cancer

The decision should be based on science, not emotions.



Tufts veterinary nutritionist Cailin Heinze, VMD, DACVN, is frustrated. “Despite what people read on the Internet,” she says, “there is no magic cancer diet. Not only is there no evidence that any specific type of diet is related to the development of cancer in dogs, there is also no clear evidence at this point that any diet can slow the progression or increase the survival of a dog with cancer.” Feeding pets with cancer is a subject very near and dear to Dr. Heinze, whose main research interest is investigating the interactions between diet and metabolism in pets with cancer, in the hopes that someday we will be able to make better nutrition recommendations for pets (and people) with that disease.

In the meantime, Dr. Heinze worries that people will inadvertently end up harming their cancer-diagnosed dogs when they mean to help. “So many pet owners, as soon as their dog is diagnosed with cancer, go on the Internet, looking in particular for how to feed them, and start making changes on their own. It’s understandable,” she says. “Cancer is scary, and people want it to be a disease they can do something about. It can be hard to accept that it’s simply in your animal’s bloodline or caused by the overlap of numerous factors too complicated to sort out at this time.

“But there’s a lot of harmful information out there, a ton of sites, supplement companies, that prey on people’s emotions, suggesting that if you don’t buy this product for your dog, you’re not giving your pet a fighting chance. Some may have a price tag of more than $100 a month. They give glowing testimonials about lives saved — but may have little or no data on efficacy or safety. You can call the company and ask if they’ve ever conducted a study on the product and they may answer ‘yes.’ But it often hasn’t been published. And a study not published is a study that for all intents and purposes hasn’t been done. Studies accepted for publication in veterinary medical journals have gone through peer review — review by scientific peers in the same field to make sure the study holds up. This process, while far from perfect, helps to identify flaws in the study design or in the way the research was carried out. Otherwise, you are forced to take the manufacturer’s word that the product does what they say that it does.”

There are also sites that aim to create a certain paranoia. “There’s a lot of that out there,” says Dr. Heinze. “These sites make claims such as ‘this is the cancer cure that THEY don’t want you to know about. We’ve been aware of this cure for 50 years, but your doctor won’t tell you.’ It’s as if the goal of all human and veterinary oncologists is for people and animals to have cancer so they stay in business. It’s terribly unfair. Both human and veterinary oncology researchers and oncology clinicians who see patients want nothing more than to find ways to keep cancer from occurring and to keep it from progressing if it does occur. They spend their lives in pursuit of that goal.”

The harm that can ensue

There are a number of so-called dietary strategies for “curing” or treating cancer that appear on many Internet sites as well as in books.

Low-carb. “A lot of blogs say we shouldn’t feed dogs with cancer any carbohydrates because carbs feed the cancer,” Dr. Heinze reports. “We have clients come in frequently who worry that if they give their dog one Milk Bone, their pet’s cancer will worsen.”

Where does this theory come from? Back in the 1920s, Nobel laureate Otto Warburg discovered that many cancer cells derive energy from a process called anaerobic glycolysis, which requires a large amount of glucose — carbohydrate broken down for use in the bloodstream. Thus, the theory goes, feeding a low-carbohydrate diet can starve cancer cells through a decrease in the supply of glucose.

The problem: in the almost 100 years that have passed since Warburg’s discovery, we still haven’t been able to prove — for any species — that feeding a diet low in carbohydrates starves cancer cells and keeps a tumor from growing, thereby extending survival time. The reason for this may be that when a dog (or person) eats, the energy from the food goes to all the cells in the body, no matter what the source of that energy. Unlike in a test tube where you can either provide glucose or not, an animal’s body has to make sure that blood glucose is high enough for all tissues; it may not be physiologically possible to make glucose low enough to really affect the cancer cells.

Granted, for most dogs, a low-carbohydrate diet is unlikely to be harmful. However, this type of diet is not ideal for all dogs with cancer. If a diet is low in carbohydrates, it tends to be relatively high in fat and protein. That can be an issue for dogs who are overweight, since fat has more than twice as many calories for its weight as carbs (or protein). Also, dogs who are prone to hyperlipidemia (too-high fat levels in the blood) as well as dogs prone to pancreatitis likely should not be eating more fat in the name of eating fewer carbohydrates. And high-protein diets may be harmful in dogs with certain types of liver disease or with kidney problems. It’s always “First, do no harm,” Dr. Heinze says.

Grain-free. Grain-free diets may be a variation on the low-carb theme. Grains are carbohydrate-rich, and grain-free diets have become popular, in part, because wolves did not eat grains in the wild before man started farming. Ergo, the thinking goes, dogs should not eat grains, either. But wolves also did not live to age 15 or longer, like companion dogs do with veterinary visits, loving human owners, and no predators to worry about. Nor did wolves in prehistoric times have veterinary nutritionists who were able to calculate their vitamin and mineral needs. Moreover, recent genetic analysis has shown that dogs are set up genetically to digest carbohydrates much more efficiently than wolves ever could. That is, their bodies are adapted to better use grains and other carbohydrate-rich foods for nourishment than wolves. And again, some grain-free diets are higher in fat than diets containing grains, which, depending on the situation, can be harmful.

Interestingly, just because

a diet is grain-free does not mean it is low in carbohydrates, even though it is often touted to be. When Dr. Heinze and colleagues at Tufts analyzed dozens of diets said to be good for dogs with cancer, about one in three of those labeled as grain-free did not meet their defined criteria for low-carbohydrate regimens (less than 20 percent of calories for a dog food). Bear in mind that carbs don’t come only from grains. They also are the main source of calories in potatoes, legumes, tapioca, vegetables, and fruits — components in a number of “grain-free” dog foods.

Raw food. While raw food is often touted as preferential to cooked for dogs with cancer, “the last thing you want is to give a raw diet to a dog who’s being administered immunosuppressant drugs like those in a chemotherapy regimen or whose immune system is compromised in the first place because of cancer,” says Dr. Heinze. When people have cancer, she says, they may be told not to go to salad bars or eat any raw fruits or vegetables they didn’t prepare in their own home. There’s too great a risk of foodborne illness arising from the presence of harmful bacteria like E. Coli, Salmonella, and Listeria, and their weakened immune system might not be able to successfully fight off the offending pathogens, which keep multiplying if left unchecked and could even cause death in some cases. “Yet,” Dr. Heinze says, “we have people coming in all the time telling us that they’re feeding their dog with cancer a raw food diet because they read they should on the Internet.” Thorough cooking kills bacteria that could otherwise cause harm.

Supplements. Vitamin and mineral supplementation is rarely necessary in dogs who are eating diets that contain all essential nutrients in adequate amounts (which include most commercial diets and home-cooked diets balanced by experienced nutritionists). Many times, when supplements are added to the diet of a pet with cancer, no one takes into account the nutrient levels that are in the dog’s main diet. More is not always better when it comes to nutrients — some nutrients can be harmful or even downright toxic.

Make the food; don’t buy it. “Many websites recommending a specific diet plan for cancer will say that commercial food is ‘bad’ and people should home-cook,” Dr. Heinze relates. The thinking is often that commercial diets contribute to cancer developing in the first place, with ingredients like preservatives named as the likely culprits. That has never been proven. On the contrary, preservatives keep food fresh and free from harmful contaminants — they keep it safe, that is, especially for dogs whose systems are already compromised due to their malignant tumors.

Of course, eschewing a commercial diet for one that’s prepared at home by a loving owner would be absolutely fine as long as the home-cooked diet were nutritionally adequate. But it hardly ever is. When Dr. Heinze and colleagues analyzed recipes for 27 home-cooked diets promoted for dogs with cancer that they found both on the web and in various books, every single one was deficient in essential nutrients. Most often it was minerals that were in short supply — calcium, magnesium, iron, copper, zinc, manganese, and selenium in particular. But adequate amounts of vitamins were missing, too. More than half the recipes were too low in vitamin D, while about 25 percent fell short in vitamin E. Also often present in inadequate concentrations: vitamin B1 (thiamine) and choline.

All of these inadequacies “have the potential to cause nutritional disease at a time when nutrition should be optimized to provide maximum metabolic support and immune system function and to help decrease adverse effects attributable to cancer treatments,” Dr. Heinze and her Tufts colleagues wrote in the prestigious Journal of the Veterinary Medical Association, where they published their research.

Shortfalls were only part of the problem. Some of the recipes were too high in certain nutrients, potentially leaving dogs open to toxicity. The most common nutrient overages occurred with vitamins D, E, and A. Too much vitamin D in a dog can result in kidney damage, for example.

Calorie levels in the home-prepared diets were all over the place, too — when enough information was given to even ascertain a calorie level. One in five recipes did not state the weight of the dog for which a serving of the food was recommended. There was no way of knowing whether the serving size was intended for a toy poodle or a Great Dane.

Stated calorie levels for a serving’s worth of food were frequently way off, too. When the scientists analyzed calorie levels, they ranged from much higher in calories than recipes stated to only a fraction of stated calories.

Finally, four of the diets either recommended or gave the option of using raw food — a huge safety issue even without nutrition concerns.

Even some commercial diets touted on the Internet and in books and magazines to be beneficial for dogs with cancer have inherent problems, as Dr. Heinze discovered when she looked at almost 40 of them. Eight contained raw meat. And only 5 percent of them had gone through feeding trials that met the standards of the Association of American Feed Control Officials (AAFCO) to insure that dogs who ate the food digested and absorbed it well enough to be benefiting from the nutrients it contained. (This is not unique to diets recommended for pets with cancer, as the majority of commercial pet foods are “formulated to meet” AAFCO guidelines rather than having been put through actual animal feeding trials. But foods put through feeding trials are out there — you have to read the fine print on the labels carefully.)

Furthermore, calorie levels in the commercial diets were a moving target, ranging from 3,300 a day to 4,900 for dry kibble — a spread of 1,600 calories.

The shame of it is that there’s no good evidence that canine cancer patients have nutrient needs that differ dramatically from those of healthy dogs to begin with. People tend to think of cancer patients as very sick and perhaps rapidly losing weight. But most dogs with cancer are not in a dire nutritional state, Dr. Heinze reports. For instance, one of the most common cancers in dogs is lymphoma. “You’re petting your dog one day and feel a lump, which is an enlarged lymph node that upon biopsy is determined to be cancer,” she says. But the dog is feeling good and eating well; he may not be not visibly sick.

Even when a dog undergoes chemotherapy, appetite may not change dramatically because dogs get lower doses of chemo for their size than people — it doesn’t have the same impact on their gastrointestinal tract. So their nutrient requirements often remain the same as when they were well. n


  1. Great article but still confused I have a non-profit animal rescue and right now we have two dogs with cancer one is lymphoma the other or not sure it’s near her mammary glands but up a little higher trying to fix the best food possible for them and supplements the easiest way because there’s a lot of dogs and animals to care for but I want to do the Best Buy these two any information extra would help greatly thank you so much


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