In July 2018, the FDA released a warning about grain-free dog foods and their possible connection to the development of a serious heart disease in dogs. Is this warning justified, based on science? Let's take a look.
What is Taurine?
Taurine is an amino acid found primarily in meat. It is abundant in the brain, the eye (especially the retina), muscle tissue, and many organs. It is an essential component of bile acids, which are produced in the liver, stored in the gallbladder, and used to break down fats from food.
Most mammals produce their own taurine from precursors. (The notable exception is cats, who must consume taurine in their diet.) The first step involves the sulfur-containing essential amino acid methionine, which is used to make another amino acid, cysteine (also spelled "cystine"). Finally, taurine is made from cysteine.
Before WWII, more than 90% of commercial pet food came in cans, and contained mostly if not only meat. However, metal was needed for the military, and by the time the war ended, 85% of pet food was dry kibble. It still contained a good amount of meat, and this is what prevented taurine deficiencies from occurring.
The primary machinery for producing what we now know as dry food is called an extruder; it was introduced in the 1950s. To get the correct consistency of dough for the extruder, the recipe called for a minimum amount of starch. This started the trend of ever-increasing quantities of cereal grain, such as corn, in dry foods. At the same time, meat processors were getting more proficient at getting more meat from livestock carcasses; so pet food makers substituted other leftover animal tissues or “by-products.” Over time, the result was a high-grain, low-meat dry food, for which the profit margin was—conveniently—much higher than for canned food.
In the late 1970s, cats started going blind or dying of congestive heart failure due to a condition called dilated cardiomyopathy (DCM). Many of those cats were eating the same food (Hill's Science Diet); and this was noticed by researchers at UC Davis. In the mid 1980s, they published the results of their research showing that taurine deficiency was the issue. Pet food manufacturers hastened to supplement taurine in their diets. Since then, DCM (dilated cardiomyopathy) dramatically decreased in cats eating commercial, "balanced" cat food. Cats can spontaneously develop DCM unrelated to taurine, and a genetic form exists in Maine coon cats and a few other breeds and lines.
Taurine and Dogs
Dogs make their own taurine from sulfur-containing amino acids, primarily cysteine, but also methionine. It was thought that, because they could produce it themselves, dogs didn’t need supplemental taurine.
However, it is also known that that big dogs produce taurine at a slower rate than small dogs, putting them at risk for a deficiency. Genetics also play a significant role, with certain breeds and family lines being predisposed to developing DCM.
The existence of a link between taurine deficiency and DCM in dogs has been known since1997—some dogs can’t supply their own taurine needs. Certain lines of spaniels, retrievers (notably Golden Retrievers), and particularly Newfoundlands, are known to develop the same taurine-dependent form of DCM that had killed thousands of cats.
DCM is a common form of heart disease in dogs, especially in large and giant breeds, who produce less taurine than smaller dogs on the same diet. Diet is a likely factor in about 20-30% of dogs with DCM, for which supplementing taurine may reverse the disease.
However, it may not be a specific taurine deficiency in the food that is a contributing factor in DCM. Some research suggests it may be insufficient cysteine that limits the dog's ability to produce taurine. Remember that dogs make cysteine from methionine, and taurine from cysteine. Any weak link in the chain of methionine, cysteine or taurine could be problematic.
Because of this dependency, only methionine has a minimum level in dog food according to current AAFCO standards; and there is also a minimum for the combination of methionine + cysteine.
L-carnitine, another amino acid found primarily in meat, may also play a role in the development of DCM in a small percentage of dogs. L-carnitine becomes unavailable in pet food through processing, and is generally not added back due to its high cost.
In early studies, most of the dogs with DCM were eating lamb and rice dog foods. Lamb has a relatively low level of sulfur-containing amino acids compared to chicken and other poultry. Another study found that dogs eating foods containing beet pulp had lower blood taurine levels.
Possible reasons for low blood taurine levels in dogs fed an otherwise "complete and balanced food" include:
- Differences in protein digestibility and bioavailability may limit available precursors
- Interference with reabsorption of taurine-containing bile acids in the gut so that more taurine is excreted
- Interaction of food and/or food form (canned vs. dry) with gut bacteria
"Most importantly, of the tens or perhaps hundreds of thousands of dogs eating "boutique" and grain-free foods, only a handful are related to the problem. It is not time to press the panic button yet, despite the media frenzy."
The Current Situation
The FDA reported a link between DCM and "grain-free" dog foods that rely heavily on potatoes, legumes, and exotic proteins. Vegan and homemade diets were also reportedly involved. This caught FDA's attention because some of the dogs were not the breeds that commonly develop DCM due to taurine deficiency, including Golden Retrievers, Labrador Retrievers, Whippets, Miniature Schnauzers, one Shih Tzu, one Bulldog, and an unspecified number of mixed-breed dogs.
Specifically, the FDA stated that "potatoes or multiple legumes such as peas, lentils, other “pulses” (seeds of legumes), and their protein, starch and fiber" were main ingredients of the food in several cases of DCM reported to the agency. Note the careful language used in its statement: potatoes are singled out, but with regard to legumes, multiple legumes and their isolated components were included in implicated diets.
Subsequently, FDA has emphasized that people should "not tak(e) intuitive leaps beyond what is explicitly stated in our public notice." That is, don't think that all legumes are problematic—just the ones specifically noted.
Unfortunately, FDA failed to indicate whether the associated foods were dry, canned, or both. But it's probably safe to assume that most or all were dry foods, since that is what most dogs are fed in the U.S. However, in the case of cats, canned foods need supplemented taurine at a much higher level than dry foods, because cats' gut bacteria interact differently with those food forms.
Based on FDA's statement and previous research, the ingredients most correlated with DCM in dogs and used in dog foods are:
Animal Products: Bison, Duck, Lamb, Kangaroo, Salmon, and Venison
Plant Products: Barley, Chickpeas, Fava Beans, Lentils, Peas, Potatoes, Rice/Rice Bran**, Tapioca
** Previous studies found taurine deficiency in dogs (and cats) eating diets containing rice or rice bran
While it was not named by FDA in this situation, beet pulp is known to decrease taurine status in dogs under some conditions.
FDA also suggested that food made by small "boutique" manufacturers were more likely to be problematic. Indeed, some of the foods I found that were guilty of "ingredient splitting" and overloading plant proteins are from small manufacturers.
It's odd that this problem should occur now, even though potatoes have been used in dog food—particularly "hypoallergenic" formulas—for decades. Even worse, many such foods also include lamb or other listed ingredient as the primary or sole animal protein. Hill's Science Diet d/d lists potatoes, potato starch, (venison, salmon, or duck), and potato protein as its first four ingredients. One would think these foods would be particularly dangerous. But… there is added taurine in these foods. Vegetarian and vegan dog foods include both taurine and carnitine. Clearly, this issue was not hard to anticipate.
Of course, correlation does not equal causation, and there may be other factors involved. There are dozens of grain-free dog foods on the market, and without knowing which brands were involved, it's impossible to know for certain which ingredients are at fault.
Unfortunately, some media reports have focused on legumes, even though potatoes are a far more common pet food ingredient. Legumes are very nutritious, and used properly, can be a very healthy dog food ingredient.
Many "boutique" grain-free diets contain two or more of the ingredients noted by FDA. For example, several salmon-based foods also contain potatoes and/or beet pulp; another lists kangaroo, kangaroo meal, peas, chickpeas, pea flour, red lentils, and green lentils as its major ingredients. If kangaroo, like lamb, is borderline on taurine, the combination of five legumes could easily outweigh the meat, and limit a dog's ability to produce taurine. Several other foods list up to five legumes/derivatives, sometimes in addition to potatoes or a listed lower-taurine meat like venison or lamb, as major ingredients.
As with cats, some dog foods are inordinately high in plant-based products and not so much meat. Certainly, plant proteins are often used to increase total protein and decrease cost in many dog foods.
Ingredients are listed by weight on the label; using multiple legumes, potatoes, or fractions thereof (a practice referred to as "splitting") allows a company to include far more plant protein than meat protein, while allowing the named meat to remain at the top of the ingredient panel. So, it may not be legumes that are the problem; rather, it may be an overwhelming amount of legumes.
Most small-manufacturer and grain-free diets are relatively high in protein, but the proportion of plant to animal sources may be a crucial factor for those foods implicated by the FDA.
There are other factors that could affect dogs' blood taurine levels. Perhaps there is some intrinsic factor in legumes and potatoes that is acting as an "anti-nutrient"—or something is happening during processing—that is causing taurine in these foods to become unavailable. Taurine from fish is diminished by heat processing; the loss is about 30%. Type of food (dry vs. canned) alters taurine bioavailability in cats through the action of gut bacteria; perhaps this is true for dogs as well. These possibilities have not been explored at all in dogs.
It is important to note that not all dogs with DCM—and not even all the dogs with very low blood levels of taurine—responded to taurine supplementation. Conversely, many of the sick dogs had normal blood taurine levels. One study concluded that " there was no clear relationship between low
The association is far more complicated than simply blaming the problem on legumes, as many news reports have done. There is clearly a relationship between genetics and one or several of the 15 above-listed ingredients, as well as the food's overall content of methionine, cysteine, l-carnitine, taurine, that is causing DCM. But no one has any idea which factors are problematic, and in what amounts or combinations. It is likely that multiple factors are involved; for example, it may take multiple listed ingredients, plus a genetic predisposition toward DCM, to develop the disease.
It does seem likely that in a product containing sufficient animal protein, taurine levels will be adequate. If a food has an animal protein at the top of the ingredient list, but also contains four or five plant proteins that—in reality—constitute the majority of total protein, thus diluting and short-changing the taurine, then that may be the real problem.
One thing that is clear from all this is that AAFCO needs to revisit its Nutrient Profiles (which are based on research published prior to 2003) and either (1) increase the minimum for methionine, (2) increase the minimum for methionine-cystine (sic), and/or (3) add a notation that cysteine and taurine are essential—or at least conditionally essential—amino acids for dogs.
Most importantly, of the tens or perhaps hundreds of thousands of dogs eating "boutique" and grain-free foods, only a handful are related to the problem. It is not time to press the panic button yet, despite the media frenzy.
However, it would be helpful if pet food manufacturers would test for the four key amino acids to ensure that levels are sufficient for all dogs, or simply supplement taurine in food for dogs, as they already do for cats.
If one is feeding a potentially taurine-deficient food, it would be a good idea to give supplemental taurine at up to 1000 mg per day for every 40 pounds of the dog's body weight. Taurine, which usually comes in capsules of 500 or 1000 mg, is very safe even at extremely high doses. It has very little taste; and is relatively easy to give.
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