Protein levels in some commercial dog foods have increased dramatically over the last 15 years. While there are many factors that drive dog food trends, this particular change occurred, at least in part, in response to pervasive (mis)perceptions that dogs are obligate carnivores [they are not] and beliefs that their diets must contain very high proportions of meat [they do not].

Feeding trends aside, what actually DO we know about correct dietary protein levels for dogs? How much is enough and are there risks to feeding too much?

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How Much is Enough?

Although precise protein levels that are optimal for dogs still elude us (probably because, like most things in science and nature, there is actually no single perfect value to be discovered), we do have a pretty good idea of dogs’ minimum protein requirements. We also have an understanding of their minimum essential amino acid requirements, thanks to companion animal nutritionists working in the early 1980’s.

Using this information, AAFCO, the organization that provides standards and nutrient profiles for pet foods, has set the minimum protein content for adult dog foods at 18 percent in a food containing 4000 kcals/kg. For growing puppies, the minimum is 22.5 percent.

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Knowing this, let’s use the example of feeding Stanley, my two-year-old Toller.

Stanley’s daily energy (calorie) requirement is approximately 1000 kcals per day. If Stanley is fed a food that contains AAFCO’s minimum level of protein (18 percent), Stanley would be consuming ~ 45 grams of protein each day. Of course, most foods contain more than the AAFCO minimum. If instead, I fed Stanley a food that contained 26 percent protein (and the same energy density), Stanley would then consume ~ 65 grams of protein a day.

Let’s bump that up to a level that is not uncommon today – 36 percent protein. When fed this food, Stanley is taking in 90 grams of protein per day. You get the picture – the difference between 45 and 90 gram is substantial; the higher protein food literally doubles Stanley’s protein intake.

For a bit of perspective, the current recommended daily intake (called the Dietary Reference Intake) of protein for me, a 125 lb. adult human female is 45 grams.

Huh.

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But, the protein content in many dog foods is 30 percent or more. Some are more than 40 percent protein. Why is this?

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A Bit of History

There have been several protein trends for dog foods over the last 50 years. Better take your Dramamine; this is going to get bumpy.

First, the protein and kidney connection…

Prior to the mid-1980’s, it was assumed that feeding a high protein diet to dogs contributed to the development and progression of chronic kidney disease. This theory originated from a set of studies in laboratory rats, rather than in dogs. (An aside; the studies used male rats that had been genetically manipulated to naturally develop kidney disease. Yeah, that is a problem).

When this theory was finally tested in dogs, it was discovered that dogs did not react like genetically-manipulated rats. Rather, using methodologies that were available and accepted at that time, researchers found that dietary protein did not appear to be a contributing factor in the progression of chronic kidney disease in dogs. This evidence was supported by studies from separate groups and included both experimental models of kidney disease and dogs with naturally-occurring kidney disease. Moreover, further work reported that feeding sufficient (not excessively high) levels of high quality protein to dogs with mild to moderate kidney disease was helpful rather than detrimental for disease management. (Score 1 for the pro-protein movement).

Next up, protein and weight loss…

Overweight conditions have become an enormous (no pun intended) problem in pet dogs. As a result, an entire body of research has accumulated that addresses dietary approaches to treating canine obesity. Some of this research has found that overweight dogs lose weight more efficiently when fed a high protein/low carbohydrate diet compared with when they are fed a diet containing more moderate levels of both nutrients. A variety of manipulations of the “high protein helps weight loss” paradigm have now been studied and have fueled a new set of over-the-counter and veterinary-prescribed foods containing elevated levels of dietary protein. (Point 2 for high protein).

Carnivorous canines…

Finally, beliefs that dogs should be fed as obligate carnivores (or as wolves; pick your myth) are pervasive. Sadly, the pet food industry has jumped onto this runaway train and now produces entire brands dedicated to the belief that protein levels in foods can never be too high (nor carbohydrate levels too low). Despite the fact that dogs’ actual protein needs are much lower, it is not unusual to find extruded dry dog foods with protein levels of 38 percent or more. Raw foods often have percentages that are even higher than this. Today, there is a plethora of commercial dog foods targeting owners who desire to feed Fluffy like the domesticated predator that they long for her to be. Not surprisingly, these foods sell very well. (It’s 3 points for the win).

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Is all of this protein really needed? Is it good for our dogs’ health?

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Revisiting Risks

The erratic pendulum of dietary protein may be swinging once again. A recent study, conducted by researchers at Kansas State University and funded by Hill’s Pet Nutrition, examined the effects of feeding three different levels of dietary protein to adult dogs on metabolomics and the gut microbiome (1).

What the heck is metabolomics?

Metabolomics, along with its close cousin, the gut microbiome, are all the rage in nutrition research these days. Metabolomics refers to the collective and analytical study of metabolites in the body. For our purposes, these are the end products of protein metabolism that are found circulating in the dog’s blood or excreted in their urine or feces. There are a lot of these and so analysis of their trends and patterns provides valuable information about an animal’s metabolic state and health.

The gut microbiome refers to all of the microorganisms naturally found in a dog’s intestinal environment. These organisms, primarily different species of bacteria, have numerous health effects and are also a direct source of many of the metabolites that are studied in metabolomics. (Note: This is new science that was not even a glimmer of a lightbulb when the earlier protein levels and kidney function work in dogs was conducted in the 1980’s and 90’s).

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So, what does this new study tell us about protein levels in dog food?

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The Study

Healthy adult dogs were fed a low (18 %), medium (25 %) or high (46 %) protein diet for 90 days. The source of the protein was dried chicken and soybean protein. The authors state in the paper that the protein sources in these foods were “high quality.” Data provided in a supplemental table support this claim; protein digestibility values were ~ 90 percent.

Results

It was theorized that feeding a high protein food would lead to an increased proportion of undigested protein reaching the large intestine, where it would be subjected to degradation by gut microbes. This could subsequently impact both the gut microbiome and the dogs’ metabolomics. Here are the major findings:

• Kidney Function: Metabolites that are identified as uremic toxins and associated with kidney dysfunction increased significantly in blood, urine and feces when dogs were fed the high protein food. While some of these compounds originate from the normal breakdown of protein in the body (i.e. urea), others were “postbiotics“, compounds produced by protein-degrading bacteria in the large intestine which are then absorbed.
• Inflammation: Feeding a high protein food resulted in significantly higher serum and urine levels of gut-derived compounds produced by proteolytic bacteria. Two of these, indole sulfate and p-cresol are classified as pro-inflammatory compounds. Simultaneously, compounds that have anti-inflammatory properties decreased in serum and urine in response to feeding the high protein diet.
• Proteolytic Gut Microbes: Fecal pH increased when dogs were fed the high protein food. This increase was expected and has been demonstrated in other studies. A protein-induced increase in intestinal pH indicates higher activity of proteolytic bacterial species (bugs that ferment protein) and reduced activity of saccharolytic bacterial species (bugs that ferment fiber and resistant starches). Several of the end products produced by protein-fermenting bacteria are considered to be potentially harmful. Similarly, there was a reduction in bacterial end products that are classified as beneficial when the high protein food was fed.

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Take Away for Dog Folks

The authors conclude that:

“the results indicate that consumption of high protein food over the long-term [results in] increases in metabolites associated with kidney dysfunction, inflammation, and proteolysis”.

How Science Works: It is important to emphasize (as the authors of this paper do) that while the metabolic changes that occurred when a high protein diet was fed are considered to be potentially harmful, all of the dogs in the study remained healthy. The measured indicators – metabolomic and gut microbiome changes – are still relatively new approaches to studying and monitoring dogs’ response to dietary changes. Although the early research (discussed previously) concluded that protein was not a significant risk factor in the progression of kidney disease in dogs, this new research forces us to take another look at this issue.

It is also of note that although the protein sources are not well described in this study (all that we are told is that the protein comes from some combination of dried chicken and soy protein), the digestibility data suggest that the foods contained high quality protein sources. Not to put too fine a point on this, but the negative effects of feeding a high protein diet will be exacerbated in foods that include protein of lower quality. This would occur because a higher proportion of poor quality protein would end up in the large intestine as substrate for protein-fermenting species of bacteria.

What to do? Personally, I take this information as evidence suggesting that our dogs should be fed high quality foods (especially protein) in which protein levels are moderate (higher than the minimum) but not excessively high. Certainly, we need additional studies and more evidence. Regardless, we should accept these data as an indication that indeed, we can actually feed too much protein to dogs.

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That said, time to pull out the box.

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The elephant in the room…..should we start examining issues of “over” nutrition in dogs?

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Here is what I mean. The study reviewed in this essay concerned dietary protein. It asked the question – Are there health risks associated with feeding too much protein to dogs? The data suggest that there could be potential harm; specifically increases in gut microbiome-derived kidney toxins and inflammatory agents.

But, protein is not the only nutrient that we should look at. In my opinion (this is a soapbox, remember), over-nutrition, providing too much of one or more essential nutrients, may be more of a problem today than we realize.

Questions of over-nutrition have been raised about several other nutrients in recent years:

• Copper (see “Considering Copper“)
• Mercury (see “Mercury Rising?“)
• Omega-3 fatty acids (both through food enrichment and pet owner supplementation). The effects of this class of fatty acids on the body’s oxidative state have been studied recently (blog essay coming soon).

And certainly, no one can claim that the over-consumption of one of the most important nutrients, calories, is not a serious health problem in dogs today (see “Do You Think I Look Fat in this Collar?“).

The pet food industry has long been held to (and has promoted) the standard of “complete and balanced”. There are several flaws with this approach, one of which may be the mandated requirement to meet every single daily essential nutrient need for dogs in a single commercial product (which, we never do with our own diets, by the way). Erring on the side of “too much” may be arising as more of a problem for our dogs than instances of too little.

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Nuff’ said. Off of Box. Carry on.

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Cited Study: Ephraim E, Cochrane C-Y, Jewell, DE. Varying protein levels influence matabolomics and the gut microbiome in healthy adult dogs. Toxins 12(8):517-532. doi: 10.3390/toxins12080517.

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