Why is my Dog Fat?

The hormone insulin regulates carbohydrate, fat, and protein metabolism by partitioning ingested calories for either use or storage.

When blood glucose levels rise, usually due to carbohydrates in the diet, the pancreas secretes insulin to partition the glucose out of the bloodstream and into muscle, liver and fat cells. Muscles and the liver store a limited amount of this glucose as glycogen. Once filled, they become insulin resistant, meaning insulin no longer partitions glucose into them.

When all muscles and the liver become insulin resistant, superfluous glucose gets partitioned to fat cells, or adipocytes, through a series of chemical reactions that converts the glucose into triglycerides. Unlike muscle cells, adipocytes typically can store much more fat than muscle cells can store glycogen.

Once the adipocytes do, however, become insulin resistant, the pancreas responds by secreting even more insulin as an attempt to get glucose out of the bloodstream, thus starting a negative feedback loop: increased insulin, insulin resistance, and fat deposits. At this point both obesity and, often, diabetes begin. Moreover, as long as insulin remains high, it acts like a lock preventing these fat deposits from being tapped for energy. If your dog is overweight, this process is why.

That a hormone drives obesity, not the conventionally understood caloric imbalance caused by gluttony and sloth, should not come as any surprise. When a dog is a growing puppy, she is obviously consuming more calories than she is burning: she is growing. Hormones – principally growth hormone – drive this growth. When her adipocytes grow, hormones – principally insulin – drive this growth as well. Hormones regulate all growth. None of this is controverted and can be read in any introductory biochemistry textbook.

Moreover, a growing body of research demonstrates that elevated insulin correlates strongly with many chronic diseases such as cancer, hypothyroidism, diabetes, arthritis, and many others.[1] This indicates that many chronic diseases may be rooted in diet.

In short, hormones drive obesity and may drive many chronic diseases. Anything that raises your dog’s insulin will, at a minimum, likely cause his fat tissue eventually to grow. Carbohydrates do this. Since we already know that dogs are carnivores, replacing carbohydrates in the diet with healthy meat makes biological sense.

[1] See for example:  Weeth, LP, et.al. 2007. “Prevalence of Obese Dogs in a Population of Dogs With Cancer.” American Journal of Veterinary Research. Apr. (68)4: 389-98. (https://www.avma.org/News/Journals/Collections/Documents/ajvr_68_4_389.pdf);

Tvarijonaviciute, A., et. al. 2012. “Obesity-Related Metabolic Dysfunction in Dogs: A Comparison with Human Metabolic Syndrome.” BMC Veterinary Research. Aug. (8): 147-55. (http://bmcvetres.biomedcentral.com/articles/10.1186/1746-6148-8-147147);

Lund, EM, et al. 2007. “Prevalence and Risk Factors for Obesity in Adult Dogs from Private US Veterinary Practices.” International Journal of Applied Research in Veterinary Medicine. 4(2): 177-86. (http://www.jarvm.com/articles/Vol4Iss2/Lund.pdf).


The Association of American Feed Control Officials (AAFCO) regulates — or perhaps more appropriately, regulates the regulation of — pet food at the state level. In essence, AAFCO is a trade association comprised of representatives from various states’ agricultural departments who individually help to regulate animal feed and pet food in their home states. Thus, although AAFCO lacks regulatory authority itself, it is comprised of officials that do have such authority. These officials meet numerous times throughout the year and establish and modify model regulations on animal feed and pet food that nearly all states adopt. The Model Pet Food Regulations establish standards of nutritional adequacy and labeling. Therefore AAFCO is the de facto regulator of pet food in most states.

Should pet food consumers rely on AAFCO? The short answer: no. AAFCO is concerned with nutritional adequacy[1], not optimization. Because of this lower threshold focus, AAFCO, like the FDA, allows things like dead zoo animals and road-kill to be introduced into pet food through innocuous sounding ingredients such as “Meat and Bone Meal”, which can include the “rendered product from mammal tissues, including bone, exclusive of any added blood, hair, hoof, horn, hide trimmings, manure, stomach and rumen contents except in such amounts as may occur unavoidably in good processing practices.”[2]This lawfully includes any dead mammal — even dead pets.

Similarly, an understanding of AAFCO’s labeling standards reveals that AAFCO’s aim may not be completely focused on making pet food labels simple for consumers to understand. For instance in a hypothetical dog food labeled “Beef Entrée for Dogs” the named ingredient “beef”, “must comprise at least 10% of the total product by weight and at least 25% of the product by weight not including the added water” so long as a qualifying word like “dinner” or “platter” is used.[3] The label undeniably implies that a majority of the meal should contain beef. How is a reasonable consumer supposed to know that a pet food manufacturer could add one of these qualifying words, and lawfully decrease the amount of beef to 25% of the total?

This unfortunate potential outcome may stem from AAFCO having the dual mandate of establishing standards for both animal feed and pet food. The former is feed for animals being raised for commercial purposes. The latter should be food for a loved family member. Perhaps they should be regulated separately.

[1] http://talkspetfood.aafco.org/faq
[2] http://talkspetfood.aafco.org/whatisinpetfood
[3] http://talkspetfood.aafco.org/readinglabels

Carnivore or Omnivore?

To determine how to feed our dogs we must first determine their natural diet. Although a body of research exists that claims dogs’ omnivorous disposition, it ignores the evolutionary and biological evidence that underscores dogs’ carnivorous nature.

The evolution of the domestic dog hints at dogs’ carnivorousness.  Humans domesticated dogs between 27,000 and 40,000 years ago.[1]   Anywhere within this range is not enough time for dogs to have evolved away from a carnivorous diet.  Similarly, this range coincides  with prehistoric humans — that is humans before the agricultural revolution, which began roughly 12,000 years ago.[2] Dogs therefore evolved for more than half of their existence alongside hunter-gatherers, who primarily ate meat, not agriculturists.

This evolutionary evidence reconciles with important genetic and anatomical clues. Domestic dogs share approximately 99.8% of their DNA with wolves and 96% with coyotes.[3] Both wolves and coyotes are carnivores.[4] Dogs fall in between them genetically. Anyone wanting to prove that dogs are not carnivores would need to discover how they are excepted from this spectrum. Outside of a few, very narrow, examples[5], no one has done so.

The anatomy and biology of dogs also underscores their carnivorous disposition. Dogs have the same digestive systems as their feral, carnivorous, cousins.[6] Dogs also share a number of other traits primarily unique to carnivores: panting, instead of sweating, to cool; lapping, instead of sipping, to drink; producing their own vitamin C, instead of consuming it; and, claws in lieu of hands or hooves.[7] Despite these overwhelming physical and behavioral signs, a number of researchers argue over the debatable position  that since dogs can digest carbohydrates, they must be omnivorous.[8]

This analysis, however, not only assumes that digestibility of a food alone determines its appropriateness in a diet, but also ignores the metabolic efficiency of that food once digested. Certain foods can be both digestible and biologically inappropriate. Such foods can lead to persistent hormonal imbalances that drive chronic conditions. Recent research shows that most chronic diseases in dogs such as kidney, liver and cardiovascular disease, as well as diabetes and arthritis, to name a few, cluster around obesity.[9]

If your dog isn’t obese, he or she is much more likely to be healthy.[10] Dogs fed a carnivorous diet do not become obese.[11] Lean dogs metabolize their food efficiently because they do not have unnaturally high levels of the hormone insulin constantly circulating through their bloodstreams.[12] Grains and sugars, though arguably digestible, are metabolically inefficient for dogs and raise insulin, thus driving obesity and illness.

Finally, proponents of the omnivorous dog ignore the observation that dogs fed carnivorously are on balance much healthier than dogs fed omnivorously. Common sense dictates that whatever diet produces the healthiest dogs is the natural diet of dogs – the starting point of our inquiry. But the science alone obviates the need for common sense.

[1] Skoglund, P., E. Ersmark, E. Palkopoulou, L. Dalén. 2015. “Ancient Wolf Genome Reveals An Early Divergence of Domestic Dog Ancestors and Admixture Into High-Latitude Breeds”. Current Biology. Jun. 25(11): 1515–19. (http://www.cell.com/current-biology/abstract/S0960-9822(15)00432-7).

[2] See generally, Diamond, J. 1999. Guns, Germs, and Steel: The Fates of Human Societies. (New York: Norton).

[3] Wright, R.K. 1993. “Molecular Evolution of the Dog Family.” Trends Genet. Jun. 9(6): 218-224. (http://www.sciencedirect.com/science/article/pii/016895259390122X).

[4] Landry, S.M., H.J. Van Kruiningen. 1979. “Food Habits of Feral Carnivores: A Review of Stomach Content Analysis.” Journal of the American Animal Hospital Association. Nov./Dec. Vol. 15: 775.

[5] See, for example, Axelsson E., et al. 2013.   “The Genomic Signature of Dog Domestication Reveals Adaptation to a Starch-Rich Diet.” Nature. (495): 360-364. (http://www.nature.com/nature/journal/v495/n7441/full/nature11837.html).

[6]Strong carnassial teeth, simple stomachs of great digestive capability, thickly muscled esophaguses, stomachs, and intestines, residual cecae, and simple non-sacculated colons.

[7]Roberts, W.C. 2000. “Twenty Questions on Atherosclerosis.” Proceedings (Baylor University. Medical Center). Apr. (13)20: 139–143.

[8] Axelsson, et. al.

[9] See, for example:

German A.J., S.L. Holden, T. Bissot, R.M. Hackett, and V. Biourge. 2007.“Dietary Energy Restriction and Successful Weight Loss in Obese Client-Owned Dogs.”Journal of Veterinary Internal Medicine. Nov./Dec. 21(6): 1174–80. (http://www.ncbi.nlm.nih.gov/pubmed/18196722).

Hansen, R.A., et. al. 2008. “Fish Oil Decreases Matrix Metalloproteinases in Knee Synovia of Dogs With Inflammatory Joint Disease.” Journal of Nutritional Biochemistry. Feb. 19(2): 101-8. (http://www.ncbi.nlm.nih.gov/pubmed/17531456).

Jeusette I.C., E.T. Lhoest, L.P. Istasse, and M.O. Diez. 2005.“Influence of Obesity on Plasma Lipid and Lipoprotein Concentrations in Dogs.”American Journal of Veterinary Research. Jan. 66(1): 81–6. (http://www.ncbi.nlm.nih.gov/pubmed/15691040).

Kealy R.D., D.F. Lawler, J.M. Ballam, S.L. Mantz, and D.N Biery, E.H. Greeley, G. Lust, M. Segre, G.K. Smith, and H.D. Stowe. 2002.“Effects of Diet Restriction on Life Span and Age-Related Changes in Dogs.” Journal of the American Veterinary Medical Association. May 220(9): 1315–20.   (http://www.ncbi.nlm.nih.gov/pubmed/11991408).

Rawitscher, R.E., W.S. Gardner, and W.H. Muller, Jr. 1973. “Experimental Canine Coronary Atherosclerosis.” Annals of Surgery. Mar. 177(3): 357-61. (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1355540/pdf/annsurg00253-0109.pdf)

Tvarijonaviciute et al. 2012. “Obesity-Related Metabolic Dysfunction in Dogs: A Comparison with Human Metabolic Syndrome.” BMC Veterinary Research. Aug. (8): 147-55. http://www.biomedcentral.com/1746-6148/8/147.;

Tvarijonaviciute et al.   2013. “Effect of Weight Loss in Obese Dogs on Indicators of Renal Function or Disease.” Journal of Veterinary Internal Medicine. Jan./Feb. (27)1: 31-8. (http://onlinelibrary.wiley.com/doi/10.1111/jvim.12029/full).

Weeth, L.P, et al. 2007.“Prevalence of Obese Dogs in a Population of Dogs With Cancer.” American Journal of Veterinary Research. 68(4): 389-98.

Yamka R.M., K.G. Friesen, and N.Z. Frantz. 2006. ”Identification of Canine Markers Related to Obesity and the Effects of Weight Loss on the Markers of Interest.” International Journal of Applied Research in Veterinary Medicine. 4(4): 282–92.

[10] Ibid.

[11] Rothwell, N.J., and M.J. Stock. 1981. “Thermogenesis: Comparative and Evolutionary Considerations.” In Cioffo, James, and Van Itallie, eds., 1981, 335-44.

[12] See, for example:

Berson, S.A. and R.S. Yalow. “Insulin ‘Antagonists’ and Insulin Resistance.” In Diabetes Mellitus: Theory and Practice, ed. M. Ellenberg and H Rifkin (New York: McGraw-Hill), 388-423. (1970).

Gordon, E.S. 1970. “Metabolic Aspects of Obesity.” Advances in Metabolic Disorders. 4: 229– 96.

Gordon, E.S. 1970 1969. “The Metabolic Importance of Obesity.” In Symposium on Foods: Carbohydrates and Their Roles, ed. H. W. Schultz. Westport, Conn.: Avi Publishing, 322– 46.

Taubes, G. 2007. Good Calories, Bad Calories: Challenging the Conventional Wisdom on Diet, Weight-Control, and Disease. (New York: Random House), 178-185.

Federal Regulation of Pet Food

According to the Food and Drug Administration (the FDA) the

…regulation of pet food is similar to that for other animal feeds. There is no requirement that pet food products have premarket approval by the FDA. However, the Federal Food, Drug, and Cosmetic Act (FFDCA) requires that pet foods, like human foods, be pure and wholesome, safe to eat, produced under sanitary conditions, contain no harmful substances, and be truthfully labeled.[1]  [Emphasis added].

The Federal Food, Drug and Cosmetic Act (the Act) defines food:

…(f) The term “food” means (1) articles used for food or drink for man or other animals…(3) articles used for components of any such article.[2] [Emphasis added].

Thus the Act that Congress passed to give the FDA its governing authority does not distinguish between food for humans and food for animals. Both should be held to the same standard.

In order for an article to be considered a food, it cannot be adulterated, which the Act also defines:

A food shall be deemed to be adulterated-
…(5) if it is, in whole or in part, the product of a diseased animal or of an animal which has died otherwise than by slaughter;…[3]

Despite this explicit ban on diseased or deceased animals not explicitly killed to become food, the FDA has determined that it will not enforce this provision of federal law:

Pet food consisting of material from diseased animals or animals which have died otherwise than by slaughter, which is in violation of 402(a)(5) will not ordinarily be actionable, if it is not otherwise in violation of the law. It will be considered fit for animal consumption.[4]

That is, if a pet food manufacturer complies with all other aspects of the Act, it can sell diseased animals and animals that died in a manner not intended for food, so long as it is cooked at an adequate temperature[5].  In other words, a dead rabid raccoon found on the roadside could lawfully be placed in your pet’s food so long as it is cooked.  You, the consumer, have no way of knowing this (more on labeling in another post).   Thus by not enforcing federal law  the FDA allows adulterated food to be used in pet food.  Unfortunately, this example is one of many of the FDA avoiding its congressional mandate with regard to pet food.  It is no wonder that pet food gets recalled so frequently.

Because we cannot rely on the federal government to protect our pet food supply, perhaps we should look to the state regulating authorities. Indeed, according to the FDA,

The best source of information about State rules is the Association of American Feed Control Officials (AAFCO). To promote uniform labeling requirements across all States and territories of the United States, AAFCO has developed a set of “Model Regulations for Pet Food and Specialty Pet Food” that are contained in AAFCO’s Official Publication. Since the AAFCO “Model Regulations” were developed consistent with Federal requirements, they are a useful resource for information on the regulation of pet food.[6]

We’ll take a look at AAFCO in a later next post.

[1] See http://www.fda.gov/ForIndustry/FDABasicsforIndustry/ucm238614.htm
[2] See 21 USC Section 321(f)
[3] See 21 USC Section 342(a)(5)
[4] See CPG Sec. 690.300
[5] Ibid.

What are Byproducts?

AAFCO defines “byproducts”, or “by-products” as “secondary products produced in addition to the principal product.”[1] In the case of pet food, byproducts are typically “the excess material left over after processing human foods.”[2]

The USDA separates animal byproducts into three categories: hides, inedible offal, and edible offal, with variety meats being a subcategory of the latter.[3] In addition to skeletal muscle, or what you typically order at the butcher for yourself, certain parts of animals are considered edible when certain conditions are met. Beef liver and tongue are two examples.

The inedible offal, or byproducts, remain and “include hide or skin, hair, horns, teeth, fats, bone, ligaments and cartilage, feet, glands, blood, and lungs” (emphasis added), as well as the otherwise edible offal that has been deemed inedible, and they may be used in pet food if they are either canned or rendered.[4] In Hill’s Science Diet Adult Light with Liver, a canned dog food, for instance, the third ingredient after water and corn, is “pork by-products”[5]. These can include any of the items just mentioned.   Moreover, save of “pork liver”, these “pork-by products” are the only meat in this dog food.

If not canned, however, the inedible animal byproducts can still be used to make pet food if they are rendered. Processors render byproduct meal by overcooking it and skimming off the fat. Sometimes the constituent animal of the byproduct meal is identified,  as in “chicken by-product meal”, “turkey by-product meal”, “beef by-product meal” and “poultry by-product meal.” (Chicken by-product meal is further subdivided into two categories: feed grade and pet food grade.) Other times this byproduct meal is identified generically, with names such as: “meat meal”, “meat and bone meal”, “meat by-product meal” and “animal by-product meal”. This byproduct meal lawfully includes, but is not limited to, road-kill, dead zoo animals, euthanized house pets and diseased livestock.

Alpo Prime Cuts Dry Dog Food, for example, contains, after corn, “meat and bone meal”[6], which according to AAFCO is a “rendered product from mammal tissues, including bone, exclusive of any added blood, hair, hoof, hide trimmings, manure, stomach and rumen contents.”[7] Neither a specific animal nor its condition is mentioned.  In short, there is no way in knowing with any degree of specificity what this ingredient is.  It could be filet mignon, or a euthanized pet.


[1] http://talkspetfood.aafco.org/byproducts
[2] Ibid.
[3] United States Department of Agriculture LDP-M-209-01; November 2011, Where the (Not) Meat? Byproducts from Beef and Pork Production. (Link).
[4] Ibid.
[5] http://www.hillspet.com/en/us/products/sd-canine-adult-light-canned
[6]  https://www.alpo.com/products/dry-dog-food/prime-cuts-dry/
[7] AAFCO, 2016 Edition, or http://www.aafco.org/Consumers/What-is-in-Pet-Food

What is Human-Grade?

AAFCO’s website nicely summarizes “human-grade” as it pertains to pet food:

There have been “human-grade” claims on some pet foods for a few years. This term has no definition in any animal feed regulations. Extremely few pet food products could be considered officially human edible or human-grade. A pet food that actually met these    standards would be expensive. While pet owners can buy what they feel is best for their pet, they should understand the definitions and the odds. [Emphasis added.]

The U.S. Department of Agriculture (USDA) defines products fit for human consumption to be officially “edible.” These foodstuffs have been processed, inspected and passed manufacturing regulations (i.e. process control regulations) that are designed to assure safety for consumption by humans.

Edible is a standard; human-grade is not. For a product to be deemed edible for humans, all ingredients must be human edible and the product must be manufactured, packed and held in accordance with federal regulations in 21 CFR 110, Current Good Manufacturing Practice in Manufacturing, Packing, or Holding Human Food. If these conditions are met for a pet food, human-grade claims may be made. If these conditions are not met, then it is an unqualified claim and misbrands the product. [Emphasis added.]

Misbranding a feed is a prohibited act subject to enforcement action on the responsible party. The presence of human-grade on a label implies a product or ingredients may meet the legally-recognized edible standard.[1]

Thus in order for a pet food to be “human-grade”, it must be legally “edible”, which pertains not only to the ingredients, but also to the conditions in which they were prepared and handled.[2]   Few pet foods meet this requirement.

Instead, most pet foods are feed-grade, or derive from “material that is safe, functional, handled, and labeled appropriately for its intended use in animal food.” By definition, this feed is inedible; that is, not safe for human consumption.

However, even if a pet food’s ingredients are “edible”, they must be prepared in accordance with Section 21 of the Congressional Federal Register, which has 100 regulations concerning food safety.  AAFCO, contrastingly, has only 15 of such regulations, which are considerably laxer.

Thus for pet food to truly be “human-grade” it needs to overcome two hurdles. First, it must be “edible”. Second, it must be prepared in accordance with regulations concerning human food. Despite many claims to the contrary, few pet foods prevail on these two tests.

[1] http://talkspetfood.aafco.org/humangrade