As veterinarians, we are often asked to recommend specific pet foods. This involves treading the line between our knowledge of canine and feline physiology, clinical studies sponsored by the pet food industry, and common sense; between an ancestral carnivore diet of small prey, and a convenient, economical diet of highly processed remnants from the human food industry. But convenience comes with a cost! The enormous increase in chronic disease, autoimmune problems, and cancer in pets over the past 60 or so years parallels the growth of the commercial pet food industry into a multi-billion-dollar business.
A recent study from Finland compared inflammatory bowel disease (IBD) incidence in a population of over 7,000 adult dogs, looking at the variable of how the dogs were fed in the first six months of life. A high-fat, low-carbohydrate non-processed meat diet fed during early life, and a normal body condition in puppyhood, were significantly associated with less IBD in adult dogs compared with those fed an ultra-processed carbohydrate based diet.1 What is an “ultraprocessed carbohydrate based diet”? Well, it turns out those terms describe almost every dry pet food, from supermarket to ultra-premium brands, and many canned foods as well. To evaluate how a commercial pet food stacks up to what a carnivore’s nutritional and physiologic needs are, we need to both understand carnivore nutrition, and interpret the actual nutritional content of a pet food beyond the often incomplete truths on the label.
LESSONS FROM UNBIASED NUTRITIONAL RESEARCH
As scientists, we like to base decisions on evidence. Unfortunately, most vet school nutrition research and boarded nutritionist specialty training depends on support from large pet food manufacturers, which creates a conflict of interest and potential bias. However, zoologists with no ties to veterinary medicine have also studied the nutrient profiles of wild canids and feral cats (“ancestral” diet) in comparison with those of domestic dogs and cats when given free choice (“instinctual” diet).2,3
The studies cited here are each meta analyses of 40 to 50 individual studies, analyzing both scat and stomach/gut contents in captured/deceased animals. While the canine study tracked the diet of wolves only, it is recognized that some other wild canids, such as foxes and jackals, do eat more plant-based foods, such as berries, which will increase the carbohydrate portion of their diets.
For wolves, the nutrient profile consumed (see Table 1) in terms of energy (percentage kcal) was found to be 54% protein, 45% fat, and 1% carbohydrate. Feral cats were found to eat 52% protein, 46% fat and 2% carbohydrate. Interestingly, the researchers found that the consumed nutrient profile did not align perfectly with the actual nutrient content of the cats’ prey, which was, on average 62% protein, 11% fat, and 13% carbohydrate. This implies that feral cats choose which body parts to eat in order to maximize the fat content.
To tease out the difference between “ancestral” and “instinctual”, several studies have been performed to assess what nutrient profile domestic dogs and cats will select in a free choice situation.4,5,6 Across a variety of breeds, dogs self-selected a macronutrient profile of 30% protein, 63% fat, and 9% carbohydrates, which is a much higher fat content than the selection consumed by wild canids. Two separate studies in cats, performed by different groups six years apart, both found remarkably similar results: 52% to 53% protein, 36% fat, and 11% to 12% carbohydrates. The nutrient selections in cats were not influenced by texture or moisture content, and the authors observed that domestic cats refused to eat more than 12% carbohydrate content free choice — in fact, they would shortchange their protein to avoid more than 12% carbs.
Interestingly, the “ketogenic” diet promoted by some to help fight cancer in pets and humans is remarkably close to the nutrient/energy ratio of an “instinctual” diet that dogs eat when given free choice. Here is the bottom line: the carbohydrate share in most commercial pet foods is four to 20 times what either feral or domestic dogs and cats would choose to consume.
BRIEF HISTORY OF THE PET FOOD INDUSTRY
In traditional societies, dogs hunted vermin as part of their jobs, and in the city, dogs were fed waste left over from turning full animal carcasses into meat — most butchers provided inexpensive “dog meat” from scraps.
Cats, of course, had a domestic contract to hunt mice and rats in the home and barn. Commercial pet food has its origins with a mid-19th century entrepreneur, James Spratt, who made grain-based biscuits for dogs based on sea-going hard biscuits for sailors, and marketed them to the wealthy aristocracy — the only demographic that might actually spend good money on dog food. Around the time of WWI and the demise of horses as the engine of commerce, Ken-L-Ration began canning horse meat as a diet for dogs. Post-WWII, the nascent food industry discovered it could use the waste products and technology of the cereal industry to make shelf-stable extruded pet foods that could be sold in a bag. In the 1960s, a comprehensive marketing campaign was effective at convincing Americans that commercial pet food was healthier than the traditional way of feeding dogs with family leftovers.
Today, there are not only pet food divisions in all the major food manufacturers, but dozens of smaller specialty pet food companies. All are competing for the vast market of US pet lovers, and the truth about their products is not nearly as appetizing as the pictures on their bags.
DECIPHERING THE LABELS
As with all commercial foods, the FDA requires that the contents (ingredients) are listed in order of weight, from large to small, on pet food labels. The guaranteed analysis (GA) is required to tell the percentage by dry weight of the food’s protein, fat, and indigestible fiber. What is not listed are carbohydrates, which are the principal component of most commercial dry pet food.
Consumers know that the first few ingredients represent the largest components of a food, so commercial manufacturers are sure to list recognizable meats, such as chicken, beef or lamb, as the first ingredient. But a tactic called “ingredient splitting” is also being employed. For instance, in one popular premium pet food, the ingredient list starts with:
Chicken, Cracked Pearl Barley, Whole Grain Wheat, Whole Grain Corn, Whole Grain Sorghum, Corn Gluten Meal, Soybean Meal, Chicken Fat, Brewer’s Rice…
The GA on this product states it contains 21% protein, but the unstated percentage of carbohydrates is calculated to be 53.5% to 61.5% (depending upon whether you use weight or energetic value for your calculations — see below).
Even though “chicken” comes first on this list, the next four ingredients are all grains, which are primarily carbohydrates. After these are two “meals” of processed plant proteins. So, it is likely that there is a vanishingly small amount of chicken in this food, after which comes a “just smaller than” amount of four grains, adding up to half the nutritional content of the food. Next comes two plant protein “meals”, which have an incomplete amino acid profile for carnivores. All the ingredients are treated with high heat, extruded and dried, and preservatives are added. Without the “loophole” of ingredient splitting, the ingredient list by weight would read:
Grain (Barley, Wheat, Corn, Sorghum), Protein Meal, Chicken…
Not even the advertising geniuses could convince pet owners that food described in this manner would be healthy for domestic carnivores.
What about grain-free pet foods?
Somehow, “grain-free” pet food evolved alongside the “gluten-free” processed food movement for humans. While there is no evidence that pets are sensitive to wheat gluten, pet owners picked up on the industry’s intention for them to infer “grain-free” as “carbohydrate-free.” This is not true in the least. Grain-free pet foods substitute legumes for grains, and use the same “splitting” techniques. Legumes contain both carbohydrates and vegetable protein, so a long list of “splits” means that the amount of animal protein in the guaranteed analysis becomes smaller and smaller. For instance, a popular super-premium grain-free dog food lists the following ingredients:
Chicken, Chicken Meal, Sweet Potatoes, Pea Protein, Pea Flour, Whole Dried Potatoes, Dried Beet Pulp, Tapioca, Flaxseed, Chicken Fat, Turkey Meal, Peas, Fish Meal…
Chicken and chicken meal are both animal protein, and are probably present in similar amounts. Next in weight are five ingredients containing carbohydrates along with plant proteins. So, if this food’s protein content is listed as 26%, it may be only 10% chicken or less. The remaining protein portion will be made up of highly-processed protein meals and plant-based protein. The rest of the top listed ingredients add up to a total of 41% carbohydrates. While this is an improvement on the 54% carbs in the example above, it is nowhere near either the ancestral nor the instinctual diet carbohydrate content of less than 10%. Protein meals are a popular ingredient in pet foods. They are products rendered from the subpar scraps left over from meat packing — rendered, concentrated, and heat-treated. Protein meals are an inexpensive source of concentrated protein, so are a favorite in the pet food industry to keep costs down while providing necessary protein for carnivores. While most bags of kibble feature photographs of beautiful cuts of meat to entice the buyer, in reality, most of the meat inside would not look like something you would be willing to eat for dinner.
What’s wrong with plant-source protein?
Each biological protein is made up of an individual profile of amino acids. “Essential” amino acids in any species are those required for health but cannot be generated in the animal’s body. Carnivores, like dogs and especially cats, have evolved over millions of years to get their essential amino acids from the bodies of their mammalian or avian prey. High heat processing denatures proteins and reduces their bioavailability.
It was discovered in the 1970s that feline dilative cardiomyopathy was due to a nutritional deficiency in taurine, an essential amino acid for cats. Cats who hunted and ate rodents or birds would get a complete and balanced diet from their prey, but those eating dried kibble were deficient until the pet food industry began dressing the kibble with extra taurine. More recently, the exaggerated scare of grain-free kibble being associated with dilative cardiomyopathy in dogs was, upon deeper examination, more likely due to the poor bioavailability of taurine, an essential canine amino acid, possibly triggered by interactions with legumes in processing. This makes more sense than thinking that grain is an essential nutrient for carnivores.
What about canned food? Isn’t that better?
Some canned foods have a better nutrient profile than dry, but sometimes the only difference between canned and dried commercial pet food is the moisture content — usually 10% in dry food and 78% in canned. When you remove the water, indigestible fiber, and mineral ingredients from the guaranteed analysis, the nutritional content of what is left becomes clearer. Many commercial canned cat foods have an acceptable nutritional profile — see catinfo.org for a spreadsheet of the actual nutritional content of many canned cat foods. However, canned pet foods are, by definition, processed with high heat, and come with other risks associated with their packaging. We now know that the plastic liners in the cans contain many toxins that can leach into the food and disrupt endocrine function. Some of the thickeners used, especially in “cuts with gravy”, are suspected to stimulate inflammatory bowel disease. (Those “meaty cuts”? They contain exactly the same ingredient mash as the paté style, but the slurry is dried and sliced in the factory. That style difference is all marketing, to make it seem more appealing to the purchaser!)
CALCULATING THE MISSING VALUES ON A PET FOOD LABEL
The US pet food industry has a powerful lobby with the FDA, which has allowed them to label processed pet food differently than food for human consumption. So you won’t see the carbohydrate content of pet food on the label guaranteed analysis. The only way to know the actual macronutrient profile of a commercial food is to pull out your calculator, or as Dr. Lisa Pierson does for catinfo.org, call the manufacturer’s customer service and insist that they supply the full information to you.
There are many other factors to consider when interpreting pet food labels. Every small nuance of wording conveys a legal meaning! For example, a label of “Turkey Dog Food” requires 95% meat or more of the total weight of all ingredients. “Turkey Recipe Dog Food” requires at least 25% percent meat, but not more than 95%; and “Turkey Flavor Dog Food” contains less than 3% percent total meat. Darwin’s Natural Pet Food has a great educational page that is well worth a perusal.
Do the math to learn the full nutrient profile of any pet food from the guaranteed analysis on the label (see sidebar on page 22 for an example of the calculations required). Compare the results in the example to the ancestral energetic ratio of wolves at 54 : 45 : 1 and the free choice instinctual canine diet energetic ratio of 30 : 63 : 9 across breeds (Table 1). See Table 2 below for a comparison of some popular commercial dry and canned pet foods with their actual macronutrient ratios. As you can see, none of the kibbles, even the super-premium brands, come close to either ancestral or instinctual nutrition ratios. The very lowest carbohydrate content dry food is still over two times what may be considered a physiologically appropriate diet for canine carnivores. And none of the cat foods have anywhere near the amount of protein cats need.
WHAT ARE THE SOLUTIONS?
We have lots of options! I tell my clients that there is a wide range of what we can feed our pets — from the ideal (sending them out to catch their own dinner) to the awful (the rancid, dusty bag of kibble that has been sitting on the shelf at the local convenience store for five years). Every family has to find the compromise that works for their lifestyle, their pet’s health, and their wallet. The family with three large dogs may choose to feed the economic dry food, but the increased risk of chronic metabolic diseases and their complications may not save money in the long run, considering vet bills. The calculation may be quite different for a small dog or cat, that literally eats less, and different again for the pet that suffers from chronic skin or GI problems, which will hugely benefit from a fresh food diet lower in carbohydrates. Homemade pet food can be a great option — if the client has the time, the motivation, and your professional support for nutrition balancing.
Beware of “home-made diet” recipes that include grains or other high glycemic index carbs as a major ingredient. Some of our older, beloved integrative textbooks have recipes that don’t stand up to modern thinking and research.
Another great option can be commercially-prepared raw food diets, either frozen or freeze-dried for convenience. The nutrient profiles on many of these are far closer to the ancestral and instinctual ones. They tend to be available at super-premium prices, however, which limits the demographic that can take advantage of them.
For clients with limited financial resources, “diluting” the high carbohydrate proportions of dry dog food with inexpensive high-fat ground beef (65/35% or 70/30% lean) can be a brilliant solution. I recommend lightly cooking such a beef product, because mass-produced ground beef as found in supermarkets commonly has Salmonella or E. coli recalls. Chicken can be a great inexpensive protein, but comes with a higher risk of Salmonella in the commercial food stream, plus many dogs with chronic inflammatory conditions may find that the warming qualities of chicken worsen their skin or GI problems. At the very least, you can ask clients to give their dogs a portion of whatever they are having, minus the starch (rice, pasta, potatoes). They could feed a couple of eggs for breakfast and some meat and vegetables for dinner. The dogs will love it and it minimizes the time commitment.
Of course, obesity is a huge health factor in a lot of our dogs and cats. Just reducing the carb ratio of their food will help normalize their metabolism and get their weight under control. When shifting the diet away from kibble, remember that dry food has at least twice the nutritional density by volume as fresh foods that are not dehydrated. So if a dog is eating two cups of kibble twice a day and maintaining a good weight, you could advise substituting one cup of dry with two cups of meat/eggs/sardines and vegetables at each meal. Fresh food is much more digestible than dry food, so you will have to monitor weight through this transition, and if the dog is gaining, take away even more kibble.
Knowledge is power! Give your clients the tools to help them choose their pets’ diets based on nutrition, not marketing!
1 Hemida M, Vuori KA, Moore R, Anturaniemi J, Hielm-Björkman A: Early life modifiable exposures and their association with owner reported inflammatory bowel disease symptoms in adult dogs. Front Vet Sci. 2021 Feb 1;8:552350.
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5 Hewson-Hughs AK, Hewson-Hughs VL, Colyer A, et al.Geometric analysis of macronutrient selection in the adult domestic cat, Felis catus. Journal of Experimental Biology. 2011; 214: 1039-1051.
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Dr. Karen Gellman is research director of Maximum Horsepower Research, which studies posture and locomotion in horses and dogs. She is a graduate of Cornell College of Veterinary Medicine, with a PhD from Cornell in animal locomotion biomechanics. She has co-taught the Postural Rehabilitation professional training course for the past eight years, and speaks to veterinarians, chiropractors and physical therapists. She is trained in acupuncture, chiropractic and other modalities and has a integrative veterinary practice in Ithaca, New York (equinesportsmed.com).