More Human-Grade Research… and a Rant

Dog foods that are produced with human-grade ingredients have increased in number and popularity in recent years. In addition to containing food ingredients that are classified and handled differently than typical pet food ingredients, these products are usually less highly processed when compared with extruded kibble (see “Human Grade Dog Foods: Some Science” for details).


To date, there are only a few studies that have examined differences between traditional (pet-grade) foods and foods produced with human-grade ingredients. I have written about two of these in earlier essays. Here are short summaries:

  • Digestibility Assay Study: A validated biological assay was used to measure macronutrient digestibilities of a set of fresh-cooked, human grade foods (Just Food For Dogs). Although dry matter digestibility values were not spectacular (possibly due to fiber content), the protein digestibility and amino acid availability values, indicators of protein quality, were very high in the human-grade foods (1).
  • Feeding Study with Dogs: In this study, two varieties of Just Food For Dogs were compared with either an extruded, dry dog food or with a fresh-cooked food produced with pet-grade ingredients (2). The two human-grade foods performed better than the extruded dry food and than the pet-grade fresh-cooked food. Digestibility values of the human-grade products were rock stars (> 90 percent), less total food was needed to maintain dogs’ body condition, and the human-grade foods produced lower volume of feces.


Another Company Publishes

The two earlier studies examined the nutritional value of a single company’s human-grade, fresh-cooked foods (Just Food For Dogs). Recently, another producer of fresh-cooked foods added their data to the growing science on this topic (3). The study compared the performance of four varieties of foods produced with human-grade ingredients (NomNomNow) to a chicken-based extruded kibble. The brand of the dry kibble was not identified. Dogs were fed each food for a period of 10 days. Collected data included measures of digestibility, energy, and fecal quality.

  • Digestibility Values: When fed to dogs, the extruded kibble had significantly lower dry matter, protein, fat and NFE (an estimate of carbohydrates) digestibility values compared with all four of the fresh-cooked products. The differences were dramatic. For example, dry matter digestibility of the kibble was ~ 82 percent. Dry matter digestibility values of all four fresh-cooked foods were 90 percent or higher.
  • Protein: Similarly, protein digestibility of the kibble was ~ 85 percent. Protein digestibility values for the four fresh foods were between 92 and 94 percent (rock star values, once again).
  • Feces: Dogs fed the fresh-cooked foods had significantly lower defecation frequencies (numbers of poops per day) and lower fecal volumes than when they were fed the kibble.

Take Away for Dog Folks

As with the earlier studies, these results suggest that foods made with human-grade ingredients that are produced with minimal processing perform well when fed to dogs. This is information that dog owners can use when evaluating and selecting healthful foods for their dogs.

Although (in my opinion) we still need controlled studies that tease out and quantify the respective influences of food processing versus initial ingredient quality, we do have a growing body of evidence telling us that both processing and ingredient quality matter in pet foods – a lot. (Remember, science loves replication). Moreover, these papers, published in academic, refereed journals, and either conducted or supported by actual pet food companies, provide great examples of industry transparency that is sadly often in short supply.

Which brings me to my soap box…….

Who produces research that we can use?

It is time to open this particular can o’ worms. I have now written about three independent studies of commercially produced, fresh-cooked human-grade dog foods. All three papers identified the companies and the brands that were tested. The data they reported included total digestibility values, protein/amino acid digestibility information, defecation frequency and fecal scores (important to many dog folks), among others. The first study showed mixed results, while the latter two demonstrated some clear wins. Moreover, although there were limitations, one study helped to tease apart the influence of ingredient quality versus that of processing. All good, practical and applicable information needed by dog folks and nutritionists alike.

So, here’s my beef (pun intended).

A common and highly (overly) shared assertion today regarding pet food selection centers on nutrition research and who exactly is doing that research. A frequent form that this “advice” takes is something along these lines (paraphrasing):

It is the large companies that employ nutritionists and that are conducting all of the research on pet food and nutrition. Therefore, consumers should trust those companies to produce safe and nutritious foods”.


There is a problem with this belief.

It is not true: The type of information that we need to know about the foods that we select for our dogs is not being provided by the large multi-national companies. Really. It is not. Please stop saying that it is.

In contrast, in recent years academic researchers, and to a lesser degree small companies, have been providing us with literally boatloads of practical information that we can use about dog nutrition, pet foods and pet food ingredients. I know this. I have been writing about it. The published research, not coming from large companies, includes, among other topics, evidence regarding protein quality, the digestibility of dried protein meals, damage due to processing, fish oils, the type of starches that are used in pet food, new processing methods such as freeze-drying and freezing, the effects of HPP on raw foods, the potential health risks of excessive copper, mercury, and contaminating thyroid hormone in pet foods, and most recently, data regarding the use of new ingredients such as insect proteins and human-grade ingredients. With the exception of a single paper (published by nutritionists with Hills), that questioned current protein levels in pet foods, I have found no recent studies by the large companies that address the nutritional value, digestibility, ingredient quality or safety of their foods or of the ingredients that they include in their foods.

For all of the marketing gimmicks, label claims, and emotional appeals that we hear from the multi-national corporations regarding the superiority of their products, where are the studies that report digestibility values, protein quality indices, and poop scores? Where are the data to support claims of nutritious and healthy foods? If we are expected to believe all of the marketing claims, then it is time for the companies (and their nutritionist spokespersons) to step up and show us the data.

Until then, I will continue to write about studies that provide helpful information to dog folks about nutrition and to thank the researchers in academia (and from small companies) that are conducting and publishing this work.

Climbing Down Now.

Cited Studies:

  1. Oba PM, Utterback PL, Parsons CM, Swanson KS: True nutrient and amino acid digestibility of dog foods made with human-grade ingredients using the precision-fed cecectomized rooster assay. Journal of Animal Science 2020; 4:442-451.
  2. Do S, Phungviwatniku T, de Godoy MRC, Swanson KS. Nutrient digestibility and fecal characteristics, microbiota, and metabolites in dogs fed human-grade foods. Journal of Animal Sciences 2021; 99,
  3. Tanprasertsuk J, Perry LM, Tate DE, Honaker RW, Shmalberg J. Apparent total tract nutrient digestibility and metabolizable energy estimation in commercial fresh and extruded dry kibble dog foods. Journal of Animal Sciences 2021; In Press.

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17 thoughts on “More Human-Grade Research… and a Rant

  1. Pingback: Can We Feed Dogs a Healthful Vegan Diet? | The Science Dog

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  3. Pingback: Do Human-Grade Dog Foods Improve Dogs’ Skin Health? | The Science Dog

  4. Hi, Linda, your columns have great meaning for me since I have a set of brother dogs and have been trying to find the best food for them. I am worn out trying to determine this. May I ask for suggestions from your readers and yourself as to the best approach and the best food that I can locate!


  5. I do enjoy your posts and always learn something 🙂. I am wondering if I missed info earlier in your series comparing digestibility of raw meat dog foods (tho I know there are MANY) with cooked meat foods? I have a Lab who had diarrhea on many different kibbles. We tried Just Food for Dogs (using human grade meat) and she did well. She is now eating a raw food diet (recipes that include supplements and veggies) and also doing well. The raw meat we use is pet quality from one of the many vendors out there. Clearly many variables there but do you have any useful data for comparison?
    Thank you!


  6. Oh, come now, the large companies do lots of studies and they have TONS of data! It’s all just… proprietary! Unless they can use it for marketing, that is. Why, just tonight, a repesentative of Purina spent an hour telling me and my colleagues how they’ve proven their food is great for pets, especially compared to their main competitor. (I can’t believe they actually gave me CE for listening to it.)

    Thanks for being a voice crying in the wilderness… we hear you, and it is greatly appreciated!

    Liked by 1 person

  7. Have I missed something? Is digestibility important? OK, it means less poo and more nutrition per kg. Is there evidence that it leads to better health outcomes?

    I hate to see the growing use of human grade materials in the dogfood industry because it makes dog ownership less sustainable. Dogs have historically been scavengers except where their owners were wealthy. Putting dogs ahead of low income people in the food chain isn’t good for the planet.

    Personally I try for the best of both by augmenting dry food with chicken frames, necks and other meaty bones from a local independent butcher … human grade but essentially a waste by-product. My dogs rarely need veterinary attention. Of course there is no scientific evidence of cause and effect. Who would pay for feeding trials involving butcher’s scraps? Also…there are too many variables. For example, fat content varies wildly in butcher’s scraps. On the other hand, commercial dog food companies have a lot to gain from convincing dog owners that their loved pet deserves the $10+ a pound quality food…and digestibility is a relatively cheap measure to quantify.


    • Yes, You have.

      Digestion (measured in a food or ingredient as “digestibility”) is how essential nutrients go from food into the body of the dog (or human, or cat, or aardvark). Digestibility is one of the reasons that you cannot feed your dog a piece of old boot leather and expect him to thrive. (Really hoping you have not tried that). For an understanding of digestion/digestibility see:

      And yes, there is evidence that digestibility is needed for health. A food that is not digested will not provide the essential nutrients or energy that an animal needs to survive. This will lead to death. Most experts agree that death is not a healthy condition for an animal to experience.

      If you prefer more nuanced evidence, there is plenty (see any basic animal nutrition textbook). Specific to dog food – there is recent evidence that the low digestibility values of some chicken meals (used in pet foods) may be so low as to cause deficiencies in certain essential amino acids when included in a food (for details see: ).

      Last, dog ownership is not made less sustainable because new ingredients are being added to the pet food market. If you have data showing that fewer people can own dogs because several companies are selling foods that use human-grade ingredients, please share it. Moreover, there are several new approaches to providing more sustainable pet food ingredients – insect proteins are one example. Reporting about the results of a study of human-grade ingredients does not mean that sustainable sources of protein are not equally of merit or interesting to study. These issues are not mutually exclusive (and I have written about sustainable ingredients previously).

      Linda Case


      • Thanks for sharing Linda.

        My concern on the narrative around digestibility in pet food marketing (and possibly what Jen is reacting to) is the focus on digestibility as a standalone quality metric when it seems more appropriate to treat it as an important factor when calculating whether the essential nutrients in the diet are being adequately provided (which I believe is your point).

        You could theoretically optimize a diet to show the highest protein and dry matter digestibility using “pure” protein forms (protein isolates, hydrolyzed proteins, synthesized amino acids, etc.), starch, and no fiber but very few would consider that the best or optimal diet (outside of some food allergy diets). I know you are not advocating to use digestibility in that way, but I can feel a digestibility ‘arms race’ coming in a way that doesn’t actually translate to better health outcomes.

        One question that we’re exploring is the usefulness of digestibility as a metric when comparing animal-derived and fungi- or plant-derived proteins. It seems like a lot of the valid focus on digestibility has come from manufacturers’ efforts to use the lowest cost animal products and the corresponding drop in digestibility due to higher ash and other processing losses. It is clearly nutritionally relevant if the ‘chicken’ ingredient listed on one label is 25% less digestible than the same ‘chicken’ ingredient listed on another label.

        However, the highest quality plant proteins have inherently lower digestibility coefficients than high-quality animal proteins, but the fiber in plants that largely causes the lower digestibility brings its own benefits. Putting aside dogs (since many of the digestibility studies for dog food used rats, mink, and roosters which are also used as human digestion models), I have not seen studies showing that the slightly lower protein digestibility of a largely plant-based diet (vs. meat-inclusive) is problematic for humans and seems to be associated with some digestive benefits.

        It seems that the digestibility metrics are very useful to describe an ingredient’s quality relative to other comparable sources (i.e. two vendors of pea protein with significantly different digestibility metrics), understand the impacts of cooking and heat, and ensuring that the dog is receiving enough essential nutrients after accounting for the digestibility loss.

        Regarding the sustainability of human-grade ingredients, I think it creates some conflict with the pet food industry’s common refrain that pet food is very sustainable because it uses otherwise wasted by-product. Driving demand for higher-value animal products will theoretically increase animal agriculture output and thus the total water, land, and greenhouse gas inputs to feed them. If the other trends around extremely high-protein, “wolf-like” diets combine with demand for human-grade meat (or at least the same skeletal muscle that humans like), you’d need a lot more chickens, cows, and lambs than we currently have.

        Thanks again for doing the heavy lifting of reviewing these studies and keeping the blog updated with your thoughtful perspective. We hope to continue to share data and research on this topic – although we need to find an acceptable alternative to using cecectomized animals every time the industry needs to measure a new diet.


        • Hi Garrett – Nice to hear from you!

          Yes, of course one can make what is essentially a “slippery slope” argument regarding food digestibility coefficients. However, as you correctly state, that is not what I or any nutritionist support. (In fact, we did produce semi-purified and purified diets for dogs when studies of essential amino acid requirements were conducted in the 80’s). Rather, digestibility is just one of the measures that can be used as an indicator of food quality.

          I agree that in today’s pet food market, the issue surrounding digestibility is centers primarily on protein quality and in particular animal protein meals and by-product products. Certainly, the amount of ash does impact quality and digestibility coefficients, but many pet food companies purchase reduced ash protein meals for their products. The bigger issue today has to do with the inclusion of protein sources that are more connective tissue than muscle meat (starting ingredients) and (in response to an increasing body of research) the damage to protein that occurs during the rendering process and extrusion. Not only does this heat treatment and excessive processing potentially reduce digestibility, but may also lead to the production of AGEs. Measuring digestibility is not a perfect reflection of protein quality but it is one important measure (there are others of course).

          Your point about plant protein sources (which are more sustainable – a good thing of course!), versus animal-source protein sources is also a good one. Since many plant proteins are not subjected to the same degree of processing that are rendered animal protein meals, it will be interesting to see the level of AGEs in the former as well as to compare overall digestibility values. When data of this type are published, I will definitely write about it! Plus, I agree that the level of various fiber types that come along with plant-source proteins may skew a digestibility value lower because of the fiber content rather than due to protein quality. (See the first paper in the series of three for related info).

          Thanks for writing – great points all!



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